Italian Contributions to Planetary Astronomy: From the Discovery of Ceres to Pluto's Orbit (Historical & Cultural Astronomy) 303148388X, 9783031483882

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Historical & Cultural Astronomy Series Editors: Wayne Orchiston · Marc Rothenberg · Clifford Cunningham

Ileana Chinnici   Editor

Italian Contributions to Planetary Astronomy From the Discovery of Ceres to Pluto’s Orbit

Historical & Cultural Astronomy Series Editors Wayne Orchiston, University of Science and Technology of China, Hefei, Anhui, China Marc Rothenberg, Smithsonian Institution (retired), Rockville, MD, USA Clifford Cunningham, University of Southern Queensland, Toowoomba, QLD, Australia Editorial Board Trudy Bell , Sky & Telescope, Lakewood, OH, USA David Devorkin, National Air and Space Museum, Smithsonian Institution, Washington, USA James Evans, University of Puget Sound, Tacoma, WA, USA Miller Goss, National Radio Astronomy Observatory, Charlottesville, USA Duane Hamacher, University of Melbourne, Clayton, VIC, Australia James Lequeux, Observatoire de Paris, Paris, France Simon Mitton, St. Edmund’s College Cambridge University, Cambridge, UK Clive Ruggles, University of Leicester, Leicester, UK Virginia Trimble, University of California Irvine, Irvine, CA, USA Gudrun Wolfschmidt, Institute for History of Science and Technology, University of Hamburg, Hamburg, Germany

The Historical & Cultural Astronomy series includes high-level monographs and edited volumes covering a broad range of subjects in the history of astronomy, including interdisciplinary contributions from historians, sociologists, horologists, archaeologists, and other humanities fields. The authors are distinguished specialists in their fields of expertise. Each title is carefully supervised and aims to provide an in-depth understanding by offering detailed research. Rather than focusing on the scientific findings alone, these volumes explain the context of astronomical and space science progress from the pre-modern world to the future. The interdisciplinary Historical & Cultural Astronomy series offers a home for books addressing astronomical progress from a humanities perspective, encompassing the influence of religion, politics, social movements, and more on the growth of astronomical knowledge over the centuries. The Historical & Cultural Astronomy Series Editors are: Wayne Orchiston, Marc Rothenberg, and Cliff Cunningham.

Ileana Chinnici Editor

Italian Contributions to Planetary Astronomy From the Discovery of Ceres to Pluto’s Orbit

Editor Ileana Chinnici Osservatorio Astronomico di Palermo INAF-National Institute for Astrophysics Palermo, Italy

ISSN 2509-310X ISSN 2509-3118 (electronic) Historical & Cultural Astronomy ISBN 978-3-031-48388-2 ISBN 978-3-031-48389-9 (eBook) https://doi.org/10.1007/978-3-031-48389-9 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Preface

Italy has a long and interesting tradition in the field of planetary astronomy and has significantly contributed to the study and exploration of Solar System bodies. The recent qualified participation of Italian scientists in many of the last space missions (DAWN, ROSETTA, EXOMARS, BEPICOLOMBO, etc.) has consolidated this tradition, which is still promising for the future. Most of the historical instruments, books and manuscripts giving evidence of this tradition—especially in the nineteenth century—are still preserved in many Italian Observatories, which are today part of INAF (National Institute for Astrophysics). Most of these materials in INAF libraries, archives, museums, and collections have not yet been sufficiently exploited, although they are fairly accessible on the web. This precious heritage offers the opportunity to carry out historical research in this field in order to fill a gap in the historiography of planetary astronomy. The currently available bibliography is in fact mainly focused on the major Italian contributions to planetary astronomy in the nineteenth century, namely, the discovery of Ceres by Giuseppe Piazzi in 1801 and the studies on Mars by Giovanni Virginio Schiaparelli in the last quarter of the nineteenth century. In contrast, nineteenth- and twentieth-century Italian studies on other topics (observations of early cometary spectra, discoveries of comets and minor planets, orbit calculations, studies of Jupiter’s surface and Saturn’s ring shape, determination of Pluto’s orbit) are almost unknown to the international community and deserve to be explored in depth. This volume intends to fill (in part) the abovementioned gap in the historiography of astronomy. Contributors are mostly historians, astronomers, and technicians working in INAF Observatories, who have easy access to local nondigitized archival resources and possess the necessary expertise for analyzing them in detail. A few nonINAF exceptions are represented by specialists in their fields, from Italy and abroad. The reason why the Italian contribution to the development of nineteenth-century planetary astronomy is mostly unknown partly lies in the scarce international circulation of the related papers and works, which was often limited by the use of the Italian language, and partly in the fact that, in general, they are (or are considered) minor contributions, with a few exceptions. This book does not pretend to be exhaustive, of course, but just to provide additional (often less-known) elements for reconstructing v

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the complex process that led to building astronomical knowledge about Solar System bodies in different chronological and geographical contexts. Moreover, it is beyond the aims of this book to provide an extended description of the development of planetary astronomy and its impact in the cultural context. However, it cannot be ignored that Galileo’s telescopic observations of the Moon, Jupiter’s satellites and Venus’s phases were the starting point of this development. Consequently, even if this book is mainly focused on the nineteenth century, the introductory chapter is a sort of tribute to Galileo, as it contains original work and new results on his telescopes. After Galileo, the most well-known Italian astronomer who worked in the field of planetary astronomy was Giovanni Virginio Schiaparelli, whose studies on Mars strongly impacted the society of the time. The second chapter describes his contributions not only to the studies of Mars but also to those, less known, of Mercury and Venus. Jesuit astronomy gave (and still gives) interesting contributions to the study of the Solar System bodies. The third chapter describes the important studies on planets and comets carried out at the Collegio Romano by Jesuit astronomers, paying special attention to the works of Father Angelo Secchi. As Florence was the most active Italian center in discovering comets, a chapter describes the Florentine contribution to cometary astronomy (and to the denial of comet-related fake news). At about half-way through the book, a fun retelling of the discovery of Ceres—the first asteroid (today classified as dwarf planet)—is a light reading after the dense initial chapters. When the photographic technique became usual in astronomy, the procedure for observing comets and asteroids changed. The Catania Observatory participated in the photographic campaign for the measurement of Eros’ parallax, which was launched during the implementation of the Carte du Ciel international project, the first attempt to photograph the entire sky vault on a global scale. The use of an astrograph and the method for measuring the positions of a celestial object on a photographic plate are described in detail in the chapter regarding the contributions of the astronomers in Turin, who discovered some minor planets around the Thirties. The last chapter resumes the most interesting contributions given by the astronomers of Padua Observatory in the field of cometary and planetary astronomy, with a double focus on the ephemerides of Biela’s comet and the calculation of Pluto’s orbit. In conclusion, this book provides information on lesser known Italian observatories, new perspectives, and microhistories that shed light on those aspects of the development of planetary astronomy in Italy in the nineteenth and early twentieth centuries that are not yet (or not at all) fully covered by the current bibliography. Palermo, Italy

Ileana Chinnici

Contents

1 A Look Back at Galileo’s Telescopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Giorgio Strano

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2 Giovanni Virginio Schiaparelli and the Planets . . . . . . . . . . . . . . . . . . . . William Sheehan and Richard McKim

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3 Planetary and Cometary Astronomy at the Collegio Romano . . . . . . . Aldo Altamore and Francesco Poppi

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4 Comet Observers in Florence in the Nineteenth Century . . . . . . . . . . . Simone Bianchi, Daniele Galli, and Antonella Gasperini

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5 The Discovery of Ceres: A “Scientific Comedy” . . . . . . . . . . . . . . . . . . . Ileana Chinnici

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6 Catania Observatory and the Italian Contribution to the Measurement of Eros’ Parallax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Manuela Coniglio 7 From Earth to the Main Asteroid Belt: The Path of Turin Astronomers in the Exploration of the Solar System . . . . . . . . . . . . . . . 117 Giuseppe Massone 8 From the Biela’s Comet to Pluto’s Orbit: The Paduan Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Simone Zaggia and Valeria Zanini

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Chapter 1

A Look Back at Galileo’s Telescopes Giorgio Strano

Abstract Galileo Galilei did not invent the telescope, but he made tremendous progress in improving and transforming it into an invaluable astronomical instrument. While the overall history of Galileo’s telescope is well known, some details on the adaptability of the instrument to the particular astronomical target being observed, as well as the actual creation of the incomparable more-than-thirty-magnification instrument mentioned in the Sidereus Nuncius, still deserve more accurate historical evaluation.

The Dutch Spyglass and Galileo In Spring 1609, Galileo Galilei—at the time an obscure lecturer of mathematics at the University of Padua—received remarkable news. His ex-pupil Giacomo Badoer (or Badouère), now a reliable correspondent from Paris, reported the invention of a certain Belgian device “by virtue of which, the visible objects, although far away from the eye of who looked inside, were distinctly seen as if they were nearby”.1 The identity of the inventor has been a matter of discussion for almost four centuries. According to historical sources, on September 25, 1608, the Committee of Councillors of the States of Zeeland wrote to the Zeeland Delegation at the StatesGeneral to recommend a special individual to Prince Maurice of Nassau. The bearer of the recommendation letter had “a certain device by means of which all things

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“[…] cuius beneficio obiecta visibilia, licet ab oculo inspicientis longe dissita, veluti propinqua distincte cernebantur”; Galileo Galilei, Sidereus Nuncius, Venice, 1610, p. 6r; also in: G. Galilei, Le Opere: Edizione Nazionale (ed. by Antonio Favaro), Florence, 1890–1909, v. 3, p. 60 (all translations from Latin are mine). I would like to thank Karen Giacobassi for her kind revision of the English text. G. Strano (B) Museo Galileo, Florence, Italy e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_1

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at a very great distance can be seen as if they were nearby”.2 On October 2, Hans Lipperhey, a citizen of Middelburg—later identified as the bearer of the letter— applied to the States-General to require a thirty-year privilege for his invention of “a certain instrument for seeing far”.3 Approximately two weeks later, on October 14, the Committee of Councillors of Zeeland took note that another young man (his name was not specified) claimed “to know the art of making instruments for seeing far things near”.4 And again, three days later, on October 17, Jacob Adriaenszoon of Alkmaar, who Latinized his name into Metius, asked for “a patent on his invention to stretch out sight in such a manner that, with it, things could be seen very clearly, which otherwise, because of the distance, could not be seen at all”.5 The States-General did not concede any privilege: all those claims made it apparent that the new device was too easily replicable. Anyway, they asked the inventors to improve it and, by noting that human beings have two eyes, also in such a way “that one could look through it with both eyes”.6 Relatively soon, the unnamed applicant of October 14 was identified as Zacharias Janssen from The Hague. He was credited as the ‘true inventor’ of the instrument by Willem Boreel, a diplomat who conducted specific investigations on the case, and by Pierre Borel, who embraced Boreel’s conclusion in his De vero telescopii inventore (The Hague, 1655–1656). Before Lipperhey was finally recognized as the ‘true inventor’, Metius also had his moment of glory in René Descartes’s Dioptrique (Leiden, 1637).7 Whoever the inventor—Badoer made no names—the news from Paris triggered Galileo’s interest. Alongside his university duties, Galileo managed either to obtain one such device,8 or to grasp its working principle deductively: a principle related 2

Letter from the Committee of Councillors of the States of Zeeland, Middelburg, to the Zeeland delegation at the States-General, The Hague, September 25, 1608; in Albert Van Helden, The Invention of the Telescope, Philadelphia, 1977, pp. 35–36. 3 Minutes of the States-General, October 2, 1608; Ibid., p. 36. The correct spelling of the applicant’s surname is “Lipperhey”; see Ibid., p. 37, Fig. 1.2. The widespread wrong spelling “Lippershey” depends on the editorial fortune of Henry C. King, The History of the Telescope, London, 1955, pp. 30 ff. 4 Minutes of the Committee of Councillors of Zeeland, October 14, 1608; in Van Helden, The Invention, cit. (n. 2), p. 38. 5 Minutes of the States-General, October 17, 1608; Ibid., p. 40. 6 Minutes of the States-General, October 2, 1608; Ibid., p. 36. 7 About these events, see: King, Op. cit. (n. 3), pp. 30–33; Van Helden, Op. cit., (n. 2), pp. 5–28; Rolf Willach, The Long Route to the Invention of the Telescope, Philadelphia, 2006, pp. 98–99; A. Van Helden, “The Beginnings, from Lipperhey to Huygens and Cassini”, in Bernhard Brandl, Remo Stuik, Jeannette Katgert-Merkelijn (eds.), 400 Years of Astronomical Telescopes: A Review of History, Science and Technology, Dordrecht, 2010, pp. 1–14: 1–5; Huib Zuidervaart, “The ‘True Inventor’ of the Telescope: A Survey of 400 Years of Debate”, in A. Van Helden, Sven Dupré, Rob van Gent, Huib Zuidervaart (eds.), The Origins of the Telescope, Amsterdam, 2010, pp. 9–44: 21–26; Peter Louwman, H. Zuidervaart, A Certain Instrument for Seeing Far, Wassenaar, 2013, pp. 9–27. 8 Perhaps, Galileo succeded in having a French specimen; Giovanni Bartoli to Belisario Vinta, August 29, 1609; in Galilei, Opere, cit. (n. 1), v. 10, p. 255.

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to the “most secret investigations of perspective”,9 or, in other words, to the “theory of refractions” (geometrical optics).10 In fact, spyglasses spread rapidly all over Europe. Devices one foot long, with a magnification up to four times, were available in Paris by April 1609.11 In May, spyglasses were brought to Milan by a Frenchman—an alleged associate of the inventor—who sold one to the Count of Fuentes.12 By July, spyglasses reached Venice and were examined by Paolo Sarpi.13 In August, the historian Lorenzo Pignoria wrote that they had been brought there by someone who came from beyond the Alps.14 According to the Tuscan ambassador Giovanni Bartoli, the same spyglasses sold in Venice for high prices could be bought in France for a few coins.15 Again, the vendor was a Frenchman.16 Spyglasses reached Naples by August. After close inspection of a specimen, Giovanni Battista Della Porta informed Federico Cesi that it was “a hoax” and that it was taken from Book 9 of his De refractione (Naples, 1653).17 Notwithstanding his superficial knowledge of geometrical optics,18 and very likely by a trial-and-error process,19 Galileo managed to improve the instrument quickly. At first, he replicated what he had either heard of or examined: I prepared for myself a lead tube, in the extremities of which I fitted two glass lenses, both flat on one side, and on the other one spherically convex, and the other concave; then, placing

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“[…] più recondite speculazioni di prospettiva”; Galileo to Leonardo Donato, August 24, 1609; Ibid., p. 250. 10 Galilei, Sidereus Nuncius, cit. (n. 1), p. 6r; also in: Galilei, Opere, cit. (n. 1), v. 3, p. 60. 11 Pierre de l’Etoile, “Journal of the Reign of Henry IV, King of France and Navarre”, entry for April 30, 1608; in Van Helden, The Invention, cit. (n. 2), p. 44. 12 Girolamo Sirtori, Telescopium, sive ars perficiendi novum illud Galilaei visorium instrumentum ad sydera, Frankfurt, 1618, pp. 24–25. 13 Paolo Sarpi to Federico Castrino, July 21, 1609; in P. Sarpi, Lettere ai protestanti (ed. by Manlio Duilio Busnelli), Bari, 1931, v. 2, p. 45. 14 Lorenzo Pignoria to Paolo Gualdo, August 1, 1609; in Galilei, Opere, cit. (n. 1), v. 10, p. 250. 15 Bartoli to Vinta, August 22, 1609; Ibid., p. 250. 16 See: Bartoli to Vinta, September 26, 1609; Ibid., p. 259. 17 “[…] è una castronaria”; Giovanni Battista Della Porta to Federico Cesi, August 28, 1609; Biblioteca dell’Accadmia dei Lincei, Roma, Mss. n. 12 (formerly Cod. Boncompagni 580), fol. 326; also in: Galilei, Opere, cit. (n. 1), v. 10, p. 252. The printed edition of the letter contains the misspelling “coglionaria”; see: Paolo Galluzzi, Libertà di filosofare in naturalibus: i mondi paralleli di Cesi e Galileo, Rome, 2014, p. 17, n.1. More importantly, there are no spyglasses in Della Porta’s De refractione. For a visual synthesis of the spread of Dutch spyglasses, see Massimo Bucciantini, Michele Camerota, Franco Giudice, Galileo’s Telescope: A European Story, Cambridge, 2015, pp. 20–21. 18 Galileo’s only document on the topic is a copy of the Theorica Speculi Concavi Sphaerici prepared by Ettore Ausonio in the 1560s; Biblioteca Nazionale Centrale, Firenze, Ms. Gal 83, c. 4r. 19 Galileo claimed that he grasped the working principle of the spyglass “per via di discorso/by a logic process”. The reasoning was, however, based on the general magnifying and reducing properties of convex and concave lenses; Galilei, Il Saggiatore, Rome, 1623, pp. 63–64; also in: Galilei, Opere, cit. (n. 1), v. 6, p. 259.

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By August 21, 1609, he had already built a better instrument, “made of tin, wrapped in red cotton fabric, about three quarte and 1/2 long [ca. 60 cm] and one scudo thick [ca. 4 cm]”.21 Galileo demonstrated the instrument to the senators of the Venetian Republic. These mature, older men climbed the bell tower of St. Mark and observed the ships approaching Venice’s harbor a couple of hours before they appeared to the naked eye.22 Four days later, on August 25, Galileo presented the instrument to the Doge. The device magnification depends on the historical source. It was ten times according to Galileo’s letter to his brother-in-law Benedetto Landucci, as “the effect of this instrument is to show an object as far as, let’s say, 50 miles, so big and near as if it is 5 miles far”.23 It was approximately eight times according to Galileo’s Sidereus Nuncius, as, in terms of surface magnification, it “showed the objects more than sixty times larger”.24 It was nine times in Galileo’s letter to the Doge because “what is far, let’s say, nine miles, appears to us as if it is only one mile far”.25 This was, perhaps, the right figure, confirmed by Antonio Priuli, the chronicler of the demonstration from St. Mark’s bell tower.26 Of course, as well as for to the original Dutch device, warfare was the suggested field of application of the improved instrument: it made it possible to spy over faraway enemy armies and ships and to organize appropriate resistance in advance.27 As a consequence of the demonstration, Galileo was rewarded with a tenured position at the University of Padua, the duplication of his salary to 1,000 florins per year,28 and a commission for twelve such improved instruments.29

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“[…] tubum […] plumbeum mihi paravi, in cuius extremitatibus vitrea duo Perspicilla, ambo ex altera parte plana, ex altera vero unum sphaerice convexum, alterum vero cavum aptavi; oculum deinde ad cavum admovens obiecta satis magna, et propinqua intuitus sum; triplo enim viciniora […] quam dum sola naturali acie spectarentur.” Galilei, Sidereus Nuncius, cit. (n. 1), p. 6r; also in: Galilei, Opere, cit. (n. 1), v. 3, pp. 60–61. 21 “[…] era di banda, foderato al di fuori di rassa gottonada cremisina, di longhezza tre quarte 1/2 incirca et larghezza di uno scudo”; Antonio Priuli’s chronicle, August 21, 1609; Ibid., v. 19, p. 587 (all translations from Italian are mine). 22 Galileo to Benedetto Landucci, August 29, 1609; Ibid., v. 10, p. 253. 23 “[…] l’effetto di questo strumento è il rappresentare quell’oggetto che è ver[bi] gratia, lontano 50 miglia, così grande e vicino come se fussi lontano miglia 5”; Ibid. 24 “[…] qui objecta plusquam sexagesis maiora repraesentabat”; Galilei, Sidereus Nuncius, cit. (n. 1), p. 6r; also in: Galilei, Opere, cit. (n. 1), v. 3, p. 61. 25 “[…] quello che è distante, v.g., nove miglia, ci apparisce come se fusse lontano un miglio solo”; Galileo to Donato, August 24, 1609; Ibid., v. 10, p. 250. 26 Priuli’s chronicle, August 21, 1609; Ibid., v. 19, p. 587. 27 Galileo to Donato, August 24, 1609; Ibid., v. 10, p. 251. 28 Galileo to Landucci, August 29, 1609; Ibid., p. 254; G. Galilei, Saggiatore, cit. (n. 19), p. 62; also in: Galilei, Opere, cit. (n. 1), v. 6, p. 258. 29 Bartoli to Vinta, September 26 and October 2, 1609; Ibid., v. 10, p. 260.

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Lenses and Magnification Who manufactured the lenses which Galileo put in his telescopes? He probably combined spectacle lenses in the first replication of the Dutch spyglass and might have used either such lenses or others commissioned to skilled spectacle makers for the instrument presented to the Doge. The many requests for powerful spyglasses which Galileo began to receive from noble and wealthy people would have inspired a different strategy. The fact that some potential customers provided good pieces of glass or rock crystal for the lenses,30 indicates that Galileo had emancipated himself from ordinary spectacle makers. This would have been the case for his next optical realization. On December 4, 1609, while planning a visit to Florence, he vaguely announced to Michelangelo Buonarroti: “I will bring with me an ameliorated occhiale”.31 What this item was, emerges from another letter, dated January 7, 1610. Galileo proudly expounded (perhaps to Antonio de’ Medici) upon his observations of the Moon, “which I have been able to see as if it was very close, that is, at a distance of less than three Earth’s diameters, because I used an occhiale which represents it [the Moon] with a diameter twenty times larger than it appears to the natural sight”.32 To achieve this goal, Galileo needed something more reliable than spectacle lenses. One piece of evidence in favour of a self-production of optical components is a memo jotted down on the address side of a letter received from Ottavio Brenzoni, dated November 23, 1609. On his next visit to Venice, Galileo would like to look for a number of commodities for his family, to buy food for stocking the pantry and to accomplish a few commissions. Remarkably, the memo also lists items for telescope making: “An organ pipe made of tin” (the tube of the instrument); “Two artillery balls” and “iron bowls, or made of stone, that is, as the artillery balls” (the moulds for grinding concave and convex lenses); “chisels” and “Tool for grinding” (indispensable to work the glass); “German ground glasses”, “rock crystal” and “Pieces of mirror” (the materials for making the lenses); “Tripoli”, “Felt, parchment for rubbing” and “Flocks of wool” (the abrasives and materials for grinding and polishing the lenses).33 Galileo should have travelled to Venice after Brenzoni’s letter was sent and delivered, that is, a few days after November 23. There is, however, no 30

See: Enea Piccolomini to Galileo, September 19, 1609; Ibid., p. 259. “Haverò meco qualche miglioramento dell’occhiale”; Galileo to Michelangelo Buonarroti, December 4, 1609; Ibid., p. 271. 32 “[…] la quale [Luna] ho potuto vedere come assai da vicino, cioè in distanza minore di tre diametri della terra, essendoché ho adoperato un occhiale il quale me la rappresenta di diametro venti volte maggiore di quello che apparisce con l’occhio naturale”; Letter from Galileo to Antonio de’ Medici (?), January 7, 1610; Ibid., p. 273. At the time, the mean Earth-Moon distance usually accepted was approximately 60 Earth radii. The magnification figure reveals that Galileo swapped Earth radii for Earth diameters. On this recurring mistake see: Edward Rosen, “Galileo on the Distance between the Earth and the Moon”, ISIS 43, 4 (1952), pp. 344–348. 33 “Canna d’organo di stagno”, “Palle d’artiglieria n.° 2”, “[…] scodelle di ferro, o di gettarle in pietre, o vero come le palle d’artiglieria”, “[…] sgubie”, “Ferro da spianare”, “Vetri todeschi spianati”, “[…] cristallo di monte”, “Pezzi di specchio”, “Tripolo”, “Feltro, specchio per fregare”, 31

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Fig. 1.1 Galileo’s schematic of the telescope (top: Biblioteca Nazionale Centrale, Florence, Ms. Gal. 48, fol. 9r; bottom: Galileo Galilei, Sidereus Nuncius, Venice, 1610, p. 7r). Note that ab/AB and cd/CD are not the lenses, but the ocular and objective ends of the telescope

evidence that the 20-magnification instrument, available from December 4, was the result of such a trip. In addition, the list by itself does not exclude that Galileo did not make lenses by himself already.34 The list proves that, in the fall of 1609, making his own lenses was a priority. If not for the 20-magnification one, the list could have been intended for the next instrument. In the Sidereus Nuncius, Galileo boldly wrote: “Finally, sparing no labor and no expense, I came to such a step that I constructed for myself an Instrument [note the capital letter!] so excellent that the objects seen through it appear nearly a thousand times larger, and more than thirty times closer than if they were observed by the natural sense [of sight] alone” (Fig. 1.1).35 Oddly, a few lines further, having mentioned the wonder of looking at the Moon as if it were only two Earth diameters away,36 Galileo invited those anxious to repeat the observations described in the Sidereus Nuncius to “necessarily prepare for themselves a perfect Perspicillum, which shows neat and distinct objects, unclouded by mist, “Follo”; On a letter from Ottavio Brenzoni to Galileo, November 23, 1609; in Galilei, Opere, cit. (n. 1), v. 10, p. 270, n. 1 (entries are not in the same order than in the memo). 34 For details on Galileo shopping list, see: Giorgio Strano, “La lista della spesa di Galileo: Un documento poco noto sul telescopio”, Galilaeana 6 (2009), pp. 197–2011; G. Strano, “Galileo’s Shopping List: An Overlooked Document about Early Telescope Making”, in Alison D. Morrison-Low, S. Dupré, Sthephen Johnston, G. Strano (eds.), From Earth-Bound to Satellite: Telescopes, Skills and Networks, Leiden, 2012, pp. 1–19; in particular, pp. 8–15. Cf. Matteo Valleriani, “L’officina astronomica di Galileo”, Le Scienze Astronomia 1 (2011), pp. 48–56: 52–54. 35 “Tandem, labori nullo nullisque sumptibus parcens, eo a me deventum est, ut Organum mihi construxerim adeo excellens, ut res per ipsum visae milles fere maiores appareant, ac plusquam in terdecupla ratione viciniores, quam si naturali tantum facultate spectentur”; Galilei, Sidereus Nuncius, cit. (n. 1), p. 6r; also in: Galilei, Opere, cit. (n. 1), v. 3, p. 61. 36 Once again, Galileo swapped Earth radii for Earth diameters; see n. 32.

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and capable of magnifying them at least four hundred times, for in that case it will show them twenty times closer”.37 The structure of the text raises some questions. What was the power of the instrument used to discover the satellites of Jupiter? If Galileo succeeded in making a perfectly working more-than-30-magnification instrument, why did he insist on the 20-magnification one, also by explaining a two-circle power test calibrated on the ratio 1 to 20?38 And why, when preparing a presentation telescope for his employer and patron, the Grand Duke of Tuscany, Cosimo II de’ Medici, did Galileo not build a more-than-30-magnification one? The first question is the easiest to answer. Galileo observed three satellites of Jupiter on January 7, 1610, and interpreted them as faint stars laying on the same straight line as the planet. This observation was announced on the same day and letter introducing the 20-magnification instrument.39 In addition, a few lines above the observation report, Galileo wrote that, soon enough, he was confident to observe the Moon in much detail than with any other instruments. In fact, he was “on the edge to complete an occhiale which will bring the Moon closer to me less than 2 diameters of the Earth”.40 That was the more-than-30-magnification telescope, which was therefore completed between January 7 and the print of the Sidereus Nuncius on March 13, 1610.41 In the Sidereus Nuncius, Galileo cannot resist mentioning such a powerful, labordemanding and expensive instrument. The impression, however, is that it was still not too satisfying. For this reason, Galileo redirected his readers to a more ‘modest’ but perfectly working instrument, hence the 20-magnification minimum required to check his celestial discoveries and the 1 to 20 power test. The doubt that the more-than-30-magnification instrument was not yet so good seems confirmed by Galileo’s letter to the Tuscan Secretary of State, Belisario Vinta. “I don’t know […] how easily [the four planets orbiting Jupiter] will be found [by the Florentine court], even if I send my most excellent occhiale, by which I observed them”.42 Was Galileo coming up with an excuse for not delivering the instrument, or was he implying that the most excellent occhiale was not so useful? Another possible confirmation comes with the telescope sent to Cosimo II on March 19, 1610, via the same Vinta. In a first version of the accompanying letter, 37

“Primo enim necessarium est, ut sibi Perspicillum parent exactissimum, quod obiecta perlucida, distincta, et nulla caligine obducta repraesentet; eademque ad minus secundum quatercentuplam rationem multiplicet; tunc enim illa bisdecuplo viciniora commonstrabit”; Galilei, Sidereus Nuncius, cit. (n. 1), p. 6v; also in: Galilei, Opere, cit. (n. 1), v. 3, p. 61. 38 Ibid. 39 Galileo to Antonio de’ Medici (?), January 7,1610; Ibid., v. 10, p. 277. 40 “[…] sendo intorno al finire un occhiale che mi avvicinerà la luna a meno di 2 diametri della terra”; Ibid. Once again, Earth diameters instead of Earth radii; see n. 32. 41 “Non prima di oggi, et ben tardi, si è potuto avere alcuna copia del mio Avviso Astronomico/Not until today, and very late, it was possible to have a copy of my Astronomical Notice”; Galileo to Vinta, March 13, 1610; Ibid., p. 288. The letter included an unbound copy of the Sidereus Nuncius. 42 “Non so […] quanto facilmente saranno trovati, se ben manderò il mio medesimo occhiale eccellentissimo, col quale li ho osservati”; Ibid., p. 289.

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Fig. 1.2 Galileo’s first observation of all four “new planets” orbiting Jupiter, made on January 13, 1610, with a 20-magnification telescope (Galileo Galilei, Sidereus Nuncius, Venice, 1610, p. 18v, detail)

Galileo wrote that he was shipping the Sidereus Nuncius (finally bound) with the dedication of the four planets orbiting Jupiter to the Medici family. The booklet came “together with the same occhiale by which I discovered the planets, and I made all the other observations (Fig. 1.2). And I send it as unadorned and badly finished as I had made it for myself and my use”.43 In a second version of the letter, the instrument was, once again, not beautiful but “very good”.44 In both cases, it is apparent that Galileo sent the 20-magnification instrument. Depriving himself of that asset for a higher cause—returning to Florence in the service of Cosimo II—would have not caused much trouble. In the first version of the letter to Vinta, Galileo specified: I also consider it indispensable to send to many princes not only the book but also the instrument […]. And, about what belongs to this detail, I still have 10 occhiali, which alone, among a hundred and more that I have made with great expense and effort, are suitable for replicating the observations of the new planets and of the fixed stars.45

The figures are different in the second version of the letter: The very exquisite occhiali, suitable for showing all the observations, are very rare. Among more than 60 that I made with great expense and effort, I have been able to select only a very small number of them. Therefore, I had intended these few to be send to great princes.46

43

“[…] insieme con quello stesso occhiale col quale ho ritrovati i pianeti et fatte tutte le altre osservazioni, et lo mando così inornato et mal pulito quale me l’havevo fatto per mio uso”; Galileo to Vinta, March 19, 1610 (ver. 1); Ibid., p. 297. 44 “[…] un occhiale assai buono”; Galileo to Vinta, March 19, 1610 (ver. 2); Ibid., p. 299. 45 “Stimo inoltre necessario il mandare a molti principi non solamente il libro, ma lo strumento ancora […]. Et in quanto appartiene a questo particolare, io mi ritrovo ancora 10 occhiali, che soli, tra cento e più che ne ho fabbricati con grande spesa e fatica, sono idonei a scoprire le osservazioni ne i nuovi pianeti et nelle stelle fisse”; Galileo to Vinta, March 19, 1610 (ver. 1); Ibid., p. 298. 46 “[…] gl’occhiali esquisitissimi et atti a mostrar tutte le osservazioni sono molto rari, et io, tra più di 60 fatti con grande spesa e fatica, non ne ho potuti elegger se non un piccolissimo numero, però questi pochi havevo disegnato di mandarli a gran principi”; Galileo to Vinta, March 19, 1610 (ver. 2); Ibid., p. 301.

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In both cases, the meaning and implications are the same. A few copies of the Sidereus Nuncius (only six, at the end) were delivered to different courts,47 together with one instrument. The attached “very exquisite occhiali” plausibly had the 20magnification power on which the booklet had been ‘calibrated’. Therefore, after sending the discovery telescope to the Grand Duke of Tuscany, Galileo had only to choose a valid replacement among a half a dozen comparable instruments. In addition, he held back the more-than-30-magnification one…48 On the one hand, after two mentions (one in print, another by letter), silence dropped for a while on the last instrument. A letter to Christoph Clavius shows that, six months later, Galileo was dealing with ameliorations.49 Whatever those were, the more-than-30-magnification instrument reappears for a third time on November 13, when Galileo informed Giuliano de’ Medici on the curious aspect of Saturn. The planet would show itself as a tri-corporal entity only “by using an occhiale which multiplies the surface more than one thousand times”.50 This necessity was later remarked to Clavius,51 while, to the contrary, the use of a 20-magnification instrument is implicit in a note on the aspect of Venus sent to Benedetto Castelli on

47

Ibid., p. 300. Rather than based on the real instrument, Sarpi’s description of the more-than-30-magnification telescope of the Sidereus Nuncius looks theoretical. “Constat, ut scis, instrumentum illud duobus perspicillis […], spaericis ambobus, altero superficiei convexae, altero concavae. Convexum accepimus ex sphaeram, cujus diameter 6 pedum, concavum ex alia cujus diameter latitudine digiti minor. Ex his componitur instrumentum, circiter 4 or pedum, per quod videtur tanta pars objecti, quae, si recta visione conspiceretur, subtenderet scrupula Ia 6. Applicato vero instrumento, videtur sub angulo majore quam 3 graduum./That instrument consists, as you know, of two lenses […], both spherical, one with a convex, and the other with a concave surface. The convex one was obtained from a sphere 6 feet in diameter, and the concave one from another [sphere] whose diameter was less than one inch. From these is made an instrument of approximately 4 feet, through which is seen so much of the object, which, if viewed with direct vision, would subtend 6 arcminutes. However, when the instrument is applied, it is seen under an angle larger than 3 degrees”; Sarpi to Jacques Leschassier, March 16, 1610, transcribed in Pierre de L’Estoile’s diary; in Galilei, Le Opere di Galileo Galilei; Appendice, vol. II: Carteggio (ed. by Michele Camerota, Patrizia Ruffo), Florence, 2015, pp. 50–51. 49 “Et havendo ultimamente perfezionato un poco più il mio strumento/Having I recently improved my instrument a little bit more”; Galileo to Cristoph Clavius, September 17, 1610; in Opere, cit. (n. 1), v. 10, p. 431. 50 “[…] servendosi di un occhiale che multiplichi più di mille volte in superficie”; Galileo to Giuliano de’ Medici, November 13, 1610; Ibid., p. 474. 51 Galileo to Clavius, December 30, 1610; Ibid., p. 500. 48

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December 30, 1610.52 Then, after a new silence, there is another mention about other ameliorations of the instrument (which one?) on February 12, 1611.53 On the other hand, there is evidence that Galileo managed fairly well to bring the 20-magnification instrument to perfection. Far from Padua, the new Primary Mathematician of the University of Pisa and Primary Mathematician and Philosopher to the Grand Duke of Tuscany had to maintain his promise: he had to present his employer and patron with a working and very beautiful telescope.54 The promise was fulfilled in July 1613, or shortly thereafter. On July 4, Andrea Cioli, the assistant of Vinta, wrote to Galileo: “The tubes for the occhiali of Your Lordship, ordered days ago according to your proposal, arrived from Paris. His Highness [Cosimo II] commanded me to send them to you, in order to put the lenses into them”.55 Galileo replied that he was momentarily ill and confined to the bed. Nevertheless, he had to consent: “I will not fail to serve His Highness as soon as I can”.56 The presentation telescope for Cosimo II still exists.57 It is one of the only two surviving telescopes made by or attributed to Galileo (Fig. 1.3).58 The short epistolary exchange between Cioli, Galileo and Vinta casts some light on the making and the date of the instrument. Very likely, once Galileo had made suitable lenses and had their optical configuration tested and measured, he designed the telescope tubes. To create a remarkably beautiful instrument, the tubes were commissioned to a French atelier, specialized in leather book binding, by the intermediation of Scipione Ammirato, a correspondent to the Medici court in Paris. The confrontation of the gilt tooling on the leather of the presentation telescope reveals, in fact, remarkable similarities with late-sixteenth- and early-seventeenth-century French books’ covers (Fig. 1.4).59

52

“Venere la veggo così spedita e terminata quanto l’istessa luna, mostrandomela l’occhiale di diametro eguale al semidiametro di essa luna veduta con l’occhio naturale/I see Venus as clearly and defined alike the Moon, because the occhiale shows it with a diameter equal to the semidiameter of the Moon seen with the natural sight”; Galileo to Benedetto Castelli, December 30, 1610; Ibid., p. 503. As the apparent diameter of the Moon is approximately 30’, and the apparent diameter of Venus at the date of the letter was approximately 40'' , the instrument magnification was 15' /0.7' = 21 times. See also: Owen Gingerich, “Phases of Venus in 1610”, Journal for the History of Astronomy 15, 1984, pp. 209–210. 53 “[…] avendo migliorato lo strumento/having I emeliorated the instrument”; Galileo to Sarpi, February 12, 1611; in Opere, cit. (n. 1), v. 11, p. 49. 54 Galileo to Vinta, March 19, 1610 (ver. 2); Ibid., v. 10, p. 299. 55 “Son venuti di Parigi quei cannoni per gli occhiali di V.S., che secondo la sua proposta si ordinarono alli giorni passati, et S.A. mi ha comandato di mandargli a lei, perché vi metta i vetri”; Andrea Cioli to Galileo, July 4, 1613; in Galilei, Opere …; Appendice, vol. II, Carteggio, cit. (n. 48), p. 126. 56 “Non mancherò di servire S.A. quanto prima potrò”; Ibid., p. 127. 57 Museo Galileo, inv. no. 2428; A. Van Helden, Catalogue of Early Telescopes, Florence, 1999, pp. 30–31. 58 The other one is inv. no. 2427; Ibid., pp. 32–33. 59 Cf.: http://www.cyclopaedia.org/virtual/bookbinding.html (accessed September 9, 2022). The Florence-Paris connection was particularly close. The Regent Queen of France, Maria de’ Medici,

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Fig. 1.3 The only two known surviving telescopes made by Galileo. (Museo Galileo, inv. no. 2427, above, and inv. no. 2428, below; © Museo Galileo, Photographic Laboratory and Archive)

Fig. 1.4 The objective housing of Galileo’s presentation telescope, partially disassembled (Museo Galileo, inv. no. 2428; © Museo Galileo, Photographic Laboratory and Archive). Note the beautiful gild tooling

The magnification of the presentation telescope is approximately 21 times. The historic records, however, reveal that in 1704 the plane-concave ocular of the instrument was loose in its housing. By the end of the eighteenth century it was lost and, thereafter, it was replaced with a biconcave ocular.60 The new lens was slightly a cousin of Cosimo II, received a spyglass made by Galileo in September 1610. As she was disappointed by its quality, a better instrument was sent in August 1611; see: Bucciantini, Camerota, Giudice, Op. cit. (n. 17), pp. 166–168. 60 Van Helden, Op. cit., (n. 57), p. 30. Note that the overall length of the telescope is not 98.0 cm, as mentioned in this Catalogue, but 92.7 cm; see: Strano, “An Overlooked Document”, cit. (n. 34), p. 12,

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Fig. 1.5 The ocular housing of Galileo’s presentation telescope, partially disassembled. Note the larger section, very similar to the objective housing, and the smaller additional section, wrapped in Florentine paper, containing the replacement ocular lens (Museo Galileo, inv. no. 2428; © Museo Galileo, Photographic Laboratory and Archive)

stronger than the lost one. For correct focusing, the nineteenth-century ‘restorer’ of the instrument added a small extension tube to the original ocular housing. It positioned the ocular lens approximately 2 cm farther from the objective lens than in the original optical configuration (Fig. 1.5). As a consequence, the power of the telescope was increased slightly. This is another clue that, in 1613, Galileo’s best telescopes still had a magnification of approximately 20 times. It is, in fact, hard to believe that Cosimo II would have contented himself with something less perfect than a state-of-the-art telescope. Once again, the magnification is confirmed in the publications. In the same year 1613, in his work on sunspots, while expounding upon the way to use the telescope for solar observations,61 Galileo also commented that Nature, “to aid us to understand her great built, granted us with more than 2000 years of observations, and a sight 20 times sharper than Aristotle’s”.62

n. 21. On Galileo’s lenses, see: Vincenzo Greco, Giuseppe Molesini, Franco Quercioli, “Modern optical testing on the lenses of Galileo”, in [no eds.], Galileo a Padova: 1592–1610, Trieste, 1995, 5 vols.: v. 5, “Occasioni Galileiane: Conferenze e Convegni, Padova, Maggio-Novembre 1992”, pp. 255–265: 256–257. On Galilo’s surviving telescopes, cf. Carlo Triarico, “Sull’attribuzione a Galileo di due telescopi galileiani conservati nell’Istituto e Museo di Storia della Scienza di Firenze”; in Marco Beretta, Paolo Galluzzi, Carlo Triarico (eds.), Musa Musei: Studies on Scientific Instruments and Collections in Honour of Mara Miniati, Florence, 2003, pp. 155–172: 158–167. 61 Galilei, Istoria e dimostrazioni intorno alle macchie solari e loro accidenti, Rome, 1613, pp. 52– 53; also in Galilei, Opere, cit. (n. 1), v. 5, pp. 136–137. 62 “[… la Natura] per aiuto all’intender la sua grande costruzione ci ha conceduti 2000 anni più d’osservazioni, e vista 20 volte più acuta, che ad Aristotele”; Galilei, Istoria e dimostrazioni, cit. (n. 56), p. 147; also in Galilei, Opere, cit. (n. 1), v. 5, p. 236.

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Drawbacks and Solutions In addition to the general tasks of keeping the lenses clean and the instrument steady,63 an indication of the main obstacle to bringing the telescope to perfection had already surfaced in the Sidereus Nuncius. It was essential that the instrument “shows neat and distinct objects, unclouded by mist”.64 Part of the solution to avoid fuzzy images— yet unmentioned in the booklet—was to place, in front of the objective, a stop with a small central hole. This was not a novelty: in Della Porta’s sketch of the Dutch spyglass, the objective side of the instrument, labelled “a”, shows a very small hole which is easily mistaken for the letter “o”.65 Galileo expounded upon the objective stop in his letter introducing the 20magnification instrument: “It is good that the thick [convex] lens, which is far from the eye, is partially covered, and that the hole which is left open is of an oval shape, because in this way the objects will be seen much more distinctly”.66 The stop was a riddle for some of Galileo’s correspondents. As an example, Clavius could not contain himself from asking: Here in Rome we have seen some occhiali sent by Your Lordship, which have very large convex lenses, but covered, with only a small hole remaining open. I wish to know why you need so much largeness if you have to cover it up like this? Someone thinks that they are made large so that, when they are completely uncovered by night, one can better see the stars.67

A few days later, Galileo responded: I made some lenses very large, although I then cover a large part of them, for two reasons: one is in order to be able to work them [the lenses] more correctly, because a large surface is better kept in the correct shape than a small one; the other is, that if you want to see more 63

“[…] è bene, per fuggire la titubatione della mano che dal moto dell’arterie et dalla respiratione stessa procede, fermare il cannone in qualche luogo stabile. I vetri si tenghino ben tersi et netti dal panno o nuola che il fiato, l’aria humida e caliginosa, o il vapore stesso che dall’occhio, et massime riscaldato, evapora, vi genera sopra/in order to overcome the trembling of the hand, caused by the pulsation of the arteries and the respiration itself, it is good to fasten the tube in some steady place. The lenses must be kept transparent and clean from the mist or opacity that the breath, the humid and hazy air, or the vapour emanating from the eye itself, especially if [the eye is] warm, deposit on it”; Galileo to Antonio de’ Medici (?), January 7, 1610; Ibid., v. 10, pp. 277–278. Galileo suggested similar cares for observing particular targets, as Venus; see: Galileo to ?, February 25, 1611; Ibid., v. 11, p. 54. 64 Galilei, Sidereus Nuncius, cit. (n. 1), p. 6v; also in: Galilei, Opere, cit. (n. 1), v. 3, p. 61. 65 Della Porta to Cesi, August 28, 1609; cit. (n. 17), fol. 326; also in: Galilei, Opere, cit. (n. 1), v. 10, p. 252. 66 “È bene che il vetro colmo, che e lontano dall’occhio, sia in parte coperto, et che il pertuso che si lascia aperto sia di figura ovale, perché così si vedranno li oggetti assai più distintamente”; Galileo to Antonio de’ Medici (?), January 7,1610; Ibid., p. 278. 67 “Si sono visti qui in Roma alcuni occhiali mandati da V.S., i quali hanno li vetri convessi assai grandi, ma coverti, con restarvi solamente un bucco piccolo libero. Desidererei di sapere che serve tanta grandezza, se ha da coprirsi in questo modo. Pensano alcuni, che siano fatti grandi, acciò scoprendosi tutti la notte, si possono meglio vedere le stelle”; Clavius to Galileo, December 17, 1610; Ibid., p. 485.

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Such a remarkable answer reveals that the instrument was not ‘static’ (by allowing, at maximum, a moderate variation of its length for focusing).69 Galileo’s telescopes had a removable stop, the presence or absence of which was decided upon observational exigencies. With the stop present: the hole at its centre selected the optimal portion of the objective and, therefore, reduced light aberrations (including astigmatism, as the oval outline of the hole suggests). With the stop removed: the maximum field of view became available, but light aberrations were reintroduced. As compensation, a single instrument had at least two interchangeable concave oculars: a strong one for high magnification, to be combined with the stop, and a weak one for lower magnification, for observations without the stop. The availability of at least two interchangeable oculars for each instrument is confirmed by another of Galileo’s previous pupils. On April 9, 1611, Daniello Antonini, now a resident in Bruxelles, informed his former teacher about the low quality of the spyglasses circulating in his region and about his spectacular 40magnification instrument made by using special iron tools (perhaps moulds).70 On September 2, Antonini wrote again that while the best spyglasses on the local market had reached a power of 10 times, his instrument, whose magnification was almost 45 times, had some faults: it does not make [things] as clear as yours [Galileo’s] did with its weaker concave lens, but a little bit more (if I recall correctly) that yours did with the stronger concave lens. In addition, it’s very hard to handle, being almost 4 braccia [ca. 2.6 m] long, and it reveals only a little portion [of the sky] as, just to say, the fourth part of the diameter of the Moon.71 68

“[…] ho fatto alcuni vetri assai grandi, benché poi ne ricuopra gran parte, et questo per 2 ragioni: l’una, per potergli lavorare più giusti, essendo che una superficie spaziosa si mantiene meglio nella debita figura, che una piccola; l’altra è, che volendo veder più grande spazio in un’occhiata, si può scoprire il vetro: ma bisogna presso l’occhio mettere un vetro meno acuto et scorciare il cannone, altrimente si vedrebbono gli oggetti assai annebbiati”; Galileo to Clavius, December 30, 1610; Ibid., pp. 501–502. 69 “È bene che il cannone si possa allungare et scorciare un poco, cioè 3 o 4 dita in circa, perché trovo che per distintamente vedere gl’oggetti vicini il cannone deve esser più lungo, et per lo lontano più corto/It is good that the tube could be lengthened and shortened a little, that is approximately 3 or 4 fingers, because I find that in order to see the nearby objects distinctly, the tube must be longer, and shorter for the faraway objects”; Galileo to Antonio de’ Medici (?), January 7,1610; Ibid., p. 278. 70 “In queste parti non si ritrovano occhiali che crescano più che 5 volte in circa la linea: tutta via i giorni passati feci io lavorarmi certi ferri, et doppo molta fatica m’è riuscito un occhiale, il qual porta più che tre braccia et mezzo di canone, et con un mediocre concavo cresce la linea circa 40 volte/In this region it’s impossible to find occhiali which magnify the line more than approximately 5 times. However, a few days ago, I commissioned some iron tools, and with much effort I made an occhiale with a tube longer than three and a half braccia [ca. 2.3 m]. With a modest concave lens, it enlarges the line approximately 40 times”; Daniello Antonini to Galileo, April 9, 1611; Ibid., v. 11, p. 84. 71 “[…] non fa chiaro quanto faceva il suo con il minor concavo, ben un poco più (se ben mi ricordo) che non faceva con il concavo maggiore. Oltre di questo, egli è dificile molto al maneggiarsi, per

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Fig. 1.6 The aspect of Saturn, Jupiter, Mars and Venus according to Galileo’s observations, very likely made by applying to the telescope a stop with a small hole and a strong ocular lens (Galileo Galilei, Il Saggiatore, Rome, 1623, p. 217, detail)

Such an adaptability implies that Galileo’s explanation to the Jesuit father Cristoph Grienberger on what the telescope does, could have been theoretically, but also technically driven: “the effect of the telescope is simply to make the aspects of the visible objects closer, by bringing them near according to the tenth, twentieth, thirtieth or another shorter or longer part of their true distance, and to show us those same objects as such as we would see them from such short distances”.72 The selected magnification depended on the quality (in glass and shape) of the objective but also on the celestial target, a star field or a planet (Fig. 1.6). It is revealing that, in the same letter, by introducing an experiment involving the observation of two curved slits— one with even margins and the other with rough margins—whose characteristics can be resolved according to the quality of the instrument,73 Galileo had a rough intuition of what will be later called the “resolution power” of the optical system. As important as the selection of the best optical set was the quality of the glass of the objective lens. On the one hand, glass quality was identified, from the beginning, as the ‘secret’ which made the difference between ordinary and excellent spyglasses.74 On the other hand, the unavailability of suitable glass was considered the limitation of early Dutch or French spyglasses.75 Those should have been Galileo’s same conclusions. In fact, he constantly looked for the best transparent material, as the central entries of his memo on Brenzoni’s letter—German glass, essere lungo quasi 4 braccia, et vede pochissimo spatio in una volta, come saria a dire la quarta parte del diametro della luna”; Antonini to Galileo, September 2, 1611; Ibid., p. 204. 72 “[…] l’effetto del telescopio non è altro se non di approssimare le specie de gl’oggetti visibili, portandocele vicine secondo la decima, vigesima, trigesima od altra minore o maggior parte della loro vera et reale lontananza, rappresentandoci i medesimi oggetti tali, quali in simili picciole distanze li vederemmo”; Galileo to Christoph Grienberger, September 1, 1611; Ibid., p. 195. 73 Ibid., pp. 198–199. 74 Bartoli to Vinta, September 26, 1609; Ibid., v. 10, p. 260. 75 Sirtori, Telescopium, cit. (n. 12), p. 25.

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rock crystal and glass for mirrors—demonstrates. Therefore, it is no surprise that Galileo’s correspondence and that of his acquaintances pullulates of notes accompanying allegedly suitable pieces of glass and lenses. Such items were received, examined, tested, discarded or accepted, sometimes either inserted in telescopes tubes or just sent back to their owners,76 and sometimes even lost by post couriers.77 On October 1, 1610, Galileo’s first justification for being unable to deliver a good telescope to Giuliano de’ Medici was the still pending move to his new house in Florence. The tools for lens making, “part of which must be affixed to the wall”, were not yet in place.78 Another justification was, however, that he was “still missing the glass, of which, in four days, on Grand Ducal commission, master Niccolò Sisti had to put a crucible in the furnace. He promised me to make the purest thing ever, excellent for such devices [telescopes]”.79 Two years later, the problem had remained the same. Requested from Cesi to make a telescope for the Bishop of Bamberg, Galileo excused himself: “I am sorry for not having crystals valid for a telescope worthy of so much Lord: […] I will see if I can do one above mediocrity, notwithstanding it is pretty hard to find pure crystal”.80 Actually, the problem remained unsolved during the seventeenth century. It was impossible to melt glass at temperatures high enough to eliminate impurities such as air bubbles, inclusions, discontinuities, colour, etcetera.

Epilogue? The fame acquired with his celestial discoveries contributed to Galileo’s success as a telescope maker. Such success was also gained from particular events, as the fact that, to verify the existence of Jupiter’s companions, which he called ‘satellites’, Johann Kepler had to borrow the telescope made by Galileo for the Elector of Cologne.81 76

See, for example: Giovanni Antonio Magini to Galileo, October 15, 1610; in Galilei, Opere, cit. (n. 1), v. 10, p. 446. 77 See the case of a lost “perfect lens”: Magini to Galileo, October 23, 1610; Ibid., p. 451. 78 “Io non sono ancora accomodato in casa […]; però non ho potuto fare accomodare miei artifizi da lavorar li occhiali, delli quali artifizi parte vanno murati, né si possono trasportare/I am not yet accommodated at home […]; for this reason, I cannot set my tools for making the occhiali, part of which must be affixed to the wall, and cannot be moved”; Galileo to Giuliano de’ Medici, October 1, 1610; Ibid., p. 440. 79 “Mi necessita ancora a indugiare il lavoro il mancamento del vetro, del quale fra quattro giorni M. Niccolò Sisti ne deve, di commissione di G.D., mettere una padella in furnace, et mi promette di fare cosa purissima et eccellente per tali artifizi”; Ibid., p. 441. 80 “Dispiacemi di non haver cristalli che vagliano per un telescopio degno di tanto Signore: […] tenterò se potrò farne un paro sopra la mediocrità, se bene ci è grandissima difficultà in trovar cristallo puro”; Galileo to Cesi, January 25, 1613; Ibid., v. 11, p. 468. The term “cristallo/crystal” refers to ‘crystal glass’, usually employed for making mirrors. 81 See: Giuliano de’ Medici to Galileo, September 6, 1610; Ibid., v. 10, pp. 427–428; Johann Kepler, Narratio de observatis a se quatuor Iovis satellitibus erronibus, quos Galilaeus Galilaeus mathematicus Florentinus iure inventionis Medicaea sidera nuncupavit, Frankfurt, 1611, fol. A2v.

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This success profited even more from the eminent personalities eager to possess telescopes and lenses made by Galileo, including the Queen of France and Emperor Rudolph II.82 This incredible reputation had cast dense shadows on Galileo’s competitors. Leaving aside those claiming the invention of the spyglass for themselves,83 the Venetian market very soon offered excellent devices. For example, in September 1611, Lodovico Cardi da Cigoli informed Galileo of the large quantity of telescopes available in the city.84 In November, Paolo Gualdo wrote to Galileo that Venetian craftsmen had found excellent ways to improve the instrument and to bring it to perfection.85 These claims were not unfounded. “I received the occhiale”, wrote Gallanzone Gallanzoni to Galileo in September 1611. “We experimented it, and it was very good, but not as good as one sent to us from Venice […], which we truly think is almost as good as yours. We compared it with many others, and, in fact, it surpasses them all”.86 A couple of years later, competitors could be found among Galileo’s closer acquaintances. In August 1613, Giovanfrancesco Sagredo had objective lenses with a focal length of almost 13 quarte (ca. 2.2 m).87 He also had a metal mould for making those lenses and, in addition, suggested to Galileo very capable Venetian lens makers who were able to satisfy any exigencies.88 In September 1613, Fabio Colonna successfully managed to make his own telescopes. He also singled out what would become the telescope-making trend during the rest of the century. In fact, Colonna privileged objectives with very long focal lengths, which he coupled to relatively weak oculars. The reverse combination—that is, a relatively short focal length objective coupled to a very strong ocular—, despite how close and large the objects observed could appear, produced dark images, deprived of any values.89 Notwithstanding the increasing number of competitors, Galileo maintained a leading position for a long while. He also gave lead to a sort of Florentine legacy, able to produce remarkable instruments up to the mid-seventeenth century, thanks to personalities as Ippolito Francini, Jacopo Mariani, and Evangelista Torricelli.90

82

Two letters from Giuliano de’ Medici to Vinta, November 14, and November 21, 1611; in Galilei, Opere, cit. (n. 1), v. 11, pp. 234–235. 83 Raffaello Gualterotti to Galileo, April 24, 1610: Ibid., v. 10, p. 341. Gualterotti claimed he invented the spyglass twelve years before the Sidereus Nuncius was printed. 84 Lodovico Cardi da Cigoli to Galileo, September 23, 1611; Ibid., v. 11, p. 212. 85 Gualdo to Galileo, November 11, 1611; Ibid., p. 230. 86 “Ho ricevuto l’occhiale […]. L’habbiamo esperimentato, et trovato bonissimo, ma non così bono come uno che fu mandato da Venetia […], che veramente crediamo che sia quasi così bono come il suo; et l’habbiamo paragonato con molt’altri, in fatti passa tutti”; Gallanzone Gallanzoni to Galileo, September 17, 1611; Ibid., p. 211. 87 Giovanfrancesco Sagredo to Galileo, August 3, 1613; Ibid., p. 549. 88 Sagredo to Galileo, August 24, 1613; Ibid., p. 553. 89 Fabio Colonna to Galileo, September 25, 1613; Ibid., p. 568. 90 See Van Helden, Catalogue, cit. (n. 57), pp. 34–39.

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In 1611, however, a major threat had silently appeared. In his Dioptrice, Kepler had theoretically introduced a new type of telescope, formed by two convex lenses.91 Only optical problems hindered and slowed down its material creation. However, once the new type of telescope found its way to being successfully produced and used—in Italy, in the 1620s by Francesco Fontana,92 —Galileo’s telescope, with its reduced field of view, becoming smaller and smaller in reverse proportion to the magnification, was condemned. As a consequence, the many specimens which Galileo had delivered to half a Europe became obsolete, and began to disappear.

91

J. Kepler, Dioptrice, seu Demonstratio eorum quae visui et visibilibus propter conspicilla non ita pridem inventa accidunt …, Augsburg, 1911, p. 44. 92 See: Paolo Del Santo, “On the Alleged Use of Keplerian Telescopes in Neaples in the 1610s”, Journal of Astronomical History and Heritage 24, 1 (2021), pp. 137–140: 139.

Chapter 2

Giovanni Virginio Schiaparelli and the Planets William Sheehan and Richard McKim

Abstract Giovanni Virginio Schiaparelli will be forever associated with the illusory network of martian canals and the captured rotation period of Mercury, about which there already exists an enormous amount of literature. But although Schiaparelli will always receive some blame for the long drawn out debate associated with the elusive, streaky martian features, he was also the first to achieve high positional accuracy in planetary mapping, and whatever stylistic drawbacks his Mars maps possess, they were based upon accurately placed details. He too was the first to compile an albedo map for Mercury.

Schiaparelli (Fig. 2.1) is now best known for his work on the planets, but he was rather late in coming to it. He had been born in Savigliano on 1835 March 14, and later dated his interest in astronomy to age four, when his father, a tile-maker, took him outside on a clear night and showed him some meteors. His interest was further stimulated when he witnessed the total eclipse of the Sun of 1842 July 8, and in his teenage years when a priest at the local church of Santa Maria della Pieve, Paolo Dovo, loaned him books and showed him the phases of Venus, the moons of Jupiter, and the rings of Saturn through a small telescope. Young Schiaparelli had already demonstrated his academic potential. Among other things, he constructed two sundials on the south facade of the church which still exist, and at age 15 was sent to the Royal University of Turin to study engineering, where he mastered the techniques of draughtsmanship and cartography which he was later to put to such good use in his work on Mars. Schiaparelli studied to be an engineer, but had always hoped for a career in astronomy. This dream was realized when one of his teachers, Quintino Sella, succeeded in obtaining a fellowship for him from the Ministry of Public Education that allowed him to continue his education in Berlin and Russia. Thus, he came W. Sheehan (B) 2655 Turtle Creek Ovi Trail, Flagstaff, AZ 86005, USA e-mail: [email protected] R. McKim 16 Main Street, Upper Benefield, Peterborough PE8 5AN, UK e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_2

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Fig. 2.1 Main illustration: Schiaparelli observing through the 49 cm Merz-Repsold refractor, installed at Brera in 1886. Top right: Schiaparelli as a young man shown upon a signed carte de visite portrait probably from the 1860s. Lower right: A more familiar view of the astronomer in middle age. Credit Authors’ collections

to learn techniques of classical astronomy, including the calculation of orbits and the micrometric observation of double stars, under Johann Franz Encke at the Berlin Observatory and Friedrich Wilhelm Struve, his son Otto Struve and F. A. T. Winnecke at Pulkovo. He returned to Italy in 1859, just as Italy’s struggle for independence with Austria was entering a critical phase, and at the battle of Solferino, a younger brother of Schiaparelli, Eugenio, was killed. At the time Italy had not yet become a nation, and the Piedmont area in which Schiaparelli had grown up was part of the Kingdom of Sardinia. However, things were changing rapidly. In 1860 June—a month after the sailing of the Thousand under Garibaldi, the turning point of the war with Austria—Schiaparelli accepted a position as assistant astronomer to Francesco Carlini at the Brera Observatory in

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Milan, and within a year, after Vittorio Emanuele, the King of Sardinia, ascended to the throne of the united kingdom of Italy as Vittorio Emanuele II, the observatory became the Royal Brera Observatory. Located in the old Brera Palace, the observatory equipment was now very dated, and included a 5-foot equatorial sector with a 4-inch (10 cm) Dollond object glass and an 8-foot mural quadrant. When after two years, Carlini died, Schiaparelli assumed the directorship (he was only twenty-seven), and began at once to try to modernize the observatory. He hoped for a refractor that would be as far as possible a twin of the 24 cm ‘Neptune’ telescope he had used in Berlin, and thanks to the intervention of Sella (now a minister in Vittorio Emanuele’s cabinet), he received funding in 1862 for a 22 cm refractor to be built by the firm of Merz. Unfortunately, there were long delays. It was not until 1874 that the telescope was finally installed on the roof of the Brera Palace. In the interim Schiaparelli made a name for himself by discovering an asteroid, Hesperia, and famously worked out that the August meteors (Perseids) followed the same orbit as the bright Comet Swift-Tuttle which had passed near the Earth in 1862. Even after his marriage to Maria Comotti in 1865, with whom he had five children and who brought with her a considerable fortune including a villa at Monticello where Schiaparelli could escape Milan’s summer heat, Schiaparelli never relaxed his complete dedication to astronomy. He was basically a workaholic. He wrote, “In my robust years, from 25 to 60, I usually worked ten hours a day. When I planned to observe I did not have dinner, but slept a while before going up to the dome as I felt it necessary to have a fresh mind and clear eyes, in order to make good observations” (Ferrari, 2011: 234). His first priority with the new refractor was resumption of the work on double stars he had learned at Berlin and Pulkova, and indeed, his conversion from double star observer to Mars observer was surprisingly casual. Having hitherto made only one sketch of Mars back in 1862, on the night of 1877 August 23, he was in the dome of the 22 cm Merz trying to measure double stars when an eclipse of the Moon got underway. During the early phases of the eclipse he noted “a horrible storm prevented us from observing double stars, and even after it ceased, the cold air, wind, and terrible images prevented us from working.” Later the sky cleared, and entering mid-eclipse, the Moon turned blood-red. Standing with it high in the sky was Mars, nearing opposition and glowing like a red coal. Shortly before midnight, Schiaparelli swung the telescope from the Moon to Mars, “only to see,” he later recalled, “whether the Merz refractor which had given such good performances on double stars, possessed the necessary optical qualities to permit the study of the surface of the planets” (Schiaparelli, 1996: 3). His first view of Mars was taken in poor air, and like most novice observers, Schiaparelli found the detail confused. He later wrote: I must confess that on comparing the aspects of the planet in view with recently published maps, this first attempt did not seem very encouraging. I had the misfortune of making my first observations on those parts of the surface of Mars that had ever been the most difficult and doubtful: the region designated in this memoir with the name of Mare Erythraeum, also that which, according to the diurnal rotation of the planet, immediately follows [it] onto the disk. At first, I didn’t know how to orient myself at all. Only later, and then with difficulty,

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Fig. 2.2 Schiaparelli’s 1877 Mars map reproduced in colour. South is uppermost (Schiaparelli 1878)

did I begin to recognize the forms on the planet which are shown in my drawings. But when I began to examine closely the very handsome sketches made by Professor Kaiser and Mr. Lockyer at the opposition of 1862, I found that the configurations they showed were almost identical to those in 1877, and in essential respects in agreement with my own. I was thus able to convince myself that … I saw the planet as others had seen it, that the apparent differences were due to the various ways observers have of representing things, and that on the whole much remained to be done on the topography of the planet, even with my limited means. I therefore resolved, on 1877 September 12, despite the fact the opposition had already passed on September 5, to make observations whenever possible… (Schiaparelli, 1996: 3).

The 1877 opposition presented the first real chance since 1862 for northern hemisphere observers to significantly add to our knowledge of the red planet. Without at first intending it, Schiaparelli, at the age of forty-two, became the world’s leading student of Mars (Fig. 2.2). Noting the deficiency of previous maps, Schiaparelli made the first attempt to establish the positions of the various albedo features through micrometrical measurements. We know today that many albedo markings are variable in form and hence position, but Schiaparelli’s ensemble from sixty-two measured points was more than sufficient to form a mapping grid of higher precision than anything previously attempted. The close attention to the planet needed in this enterprise inevitably revealed numerous small details that had not been recognised by previous observers, and—necessity being the mother of invention—required him to introduce (at first

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informally) new names for them. Previous schemes of nomenclature, such as that proposed by the English astronomer Richard Anthony Proctor, had used the names of astronomers (in some cases still living), such as ‘Beer Continent’, ‘Herschel II. Strait’, ‘Arago Strait’, ‘Lockyer Sea’, ‘Kaiser Sea’. Schiaparelli, a remarkable linguist as well as astronomer, steeped in the mythology and geography of the classical world and known to relax by composing epistles in Latin hexameters to his friends, began using his own set of names for all the many new features he was discovering with his telescope. Taken from the Odyssey, from the legends of the Argonauts, from the Old Testament and from Herodotus’ Histories, they may have been meant at first only as his own private shorthand, but eventually he became fond of them. The following table compares a few of the Proctor and Nathaniel Green names in the left column with Schiaparelli’s names in the right column. Proctor/Green

Schiaparelli

Beer Continent

Aeria and Arabia

Herschel II. Strait

Sinus Sabaeus

Arago Strait

Margaritifer Sinus

Burton Bay

Mouth of the Indus

Mädler Continent

Chryse, Ophir, Tharsis

Christie Bay

Aurorae Sinus

Lockyer Sea

Solis Lacus

Jacob Land

Noachis and Argyre I

Phillips Island

Deucalionis Regio

Hall Island

Protei Regio

Schiaparelli Sea

Mare Sirenum, Lacus Phoenicis

Maraldi Sea

Mare Cimmerium

Lockyer Land

Hellas

De La Rue Ocean

Mare Erythraeum

Kaiser Sea

Syrtis Major

Schiaparelli built better than he knew, and the nomenclature he invented—“a chimera of euphonic names, whose sounds awaken in the mind so many memories”, as he said—over time proved irresistible, and they are still the basis of those used today. The other thing that Schiaparelli introduced on his map was a set of at first winding streaks (and in later efforts increasingly narrow, regular, and double lines), which – following his basic scheme of referring to the darker features of Mars as ‘seas’ and the lighter ones as ‘lands’ – he referred to as canali, ‘channels’. (It can also mean ‘canals’, and this was the term adopted in the English and American literature). Despite criticisms from other astronomers, notably the English astronomer-artist Nathaniel Green, Schiaparelli defended the reality of these markings until the end of his life, and rather directly (if unintentionally) inspired the idea of a vast irrigation system built by the denizens of the planet (associated especially with Percival

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Lowell). It seems likely that Schiaparelli’s application of micrometric methods and surveyor’s instruments of rule and compass to rendering the features of the planet may have contributed to the exotic forms he depicted. In the great Memoir (the first of six devoted to Mars) he published of his observations from 1877 September and 1878 March, he not only introduced his map with the nomenclature and canali but also paid close attention to the ephemeris of the planet, its rotation period and the exact coordinates of the martian poles. Much later, when in 1907 Earl C. Slipher started taking photographs for Percival Lowell, Schiaparelli urged that the telescope’s drive be turned off to let Mars trail each plate, so that the all-important position angle could be accurately established photographically. He was well-read in the literature of the planet and expended much effort in making a detailed comparison of his own results with the best previous studies. In mapping Mars, Schiaparelli—or rather his printing firm in Milan—laid down the ‘seas’ in a uniform blue-grey ground, adding spurious weight to the telescopic interpretation of their colour. His outline map in the first Memoir was simply that: cardinal points, outlines and names, with no attempt at showing fine albedo differences. We now know that subjective colour contrast plays tricks in any telescopic image, especially for Mars where there are strong colours and contrasts, and that the maria (‘seas’) in reality are more neutral-toned. It is their contrast with the reddish desert areas that suggests to the eye a cold blue or green tone indicative of deep water or vegetation. In assigning the features impressive-sounding names from classical mythology he inevitably compounded the impression (deliberate or not) that they were as sharply demarcated as lands and seas on Earth are (though he also recognised half-tone areas that he interpreted as shallow seas or marshes). It is also important to remember that Schiaparelli’s drawings and maps were not known in their original forms but as transformed (usually for the worse) by the process of reproducing them. Soon after the 1877 opposition, the well-known British amateur T. W. Webb compared Schiaparelli’s map to that of Nathaniel Green, whose famous artistic-looking map was based on his observations from the island of Madeira and published by the Royal Astronomical Society in London. Said Webb: “Green has produced a picture, Schiaparelli a plan”. Schiaparelli would later admit to the famed American observer E. E. Barnard when the latter visited Brera in 1893, that he was dissatisfied with the efforts of his publishers. And if one looks at his original observations, which are still extant, they look much more natural than the engravings. Also, for the publication of his drawings and maps in the RAS Memoirs, Green personally prepared the drawings upon stone for the chromolithographs, and so had much greater control over the result. In his own manner to maintain control by the artist, the great planetary observer E. M. Antoniadi in the 1890s, would develop and make famous his stippling style, where printers could easily and cheaply produce every point of the drawing in the text of an article without resort to publishing a costly half-tone plate. He used this method to the end of his life in reproducing his drawings upon the cheap paper habitually used by the Société Astronomique de France in its Bulletin. But Schiaparelli—at least at the start—left it all to the local Milan engravers, and so the unnatural looking figures published in his first Memoir were promulgated in copies in popular works over the

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next decades. By the third Memoir, devoted to the Mars opposition of 1881–82 (at which he first introduced to the world the bizarre doubling, or geminations, of many of the canals), the illustrations began to be reproduced from the original drawings, but by then the damage had been done. One wonders whether, if photographic copies of the original drawings been published at the outset, the canal debate might have been a much more low-key affair, and even whether Percival Lowell would have been quite as inspired by the reproductions of Schiaparelli’s work in Flammarion’s compendious La Planète Mars (1892) to found his observatory and aspire to become the great successor to the Italian astronomer he admired above all others. We do not need to return here to the great Martian canal debate in detail or discuss the ‘Mars furore’ of the late nineteenth century, as the literature on that is already voluminous (Sheehan, 1988). That the canali recorded by Schiaparelli, at least in many cases, have a basis in underlying networks of small spots and patches was explained and illustrated long ago by Antoniadi. But it is reasonable to ask whether Schiaparelli himself believed in the artificiality of the canali. Not at first, it seems. Indeed, he had not even been the first to apply that term to Mars. Rather, that had been his friend Father Angelo Secchi at the observatory of the Collegio Romano, who used it as a descriptive term for some features he recorded in 1858. In later years Schiaparelli often emphasized his own preference to regard them as natural features, though at the same time he was careful not to rule out the possibility of artificial construction. In his own words, “I am careful not to combat that supposition, which contains nothing impossible.” One seems to detect a subtle shift in his views over time, from agnosticism to near-belief, especially after he entered into an increasingly warm correspondence with Lowell. One senses this from a close reading of their correspondence between 1896 and 1910. (Putnam & Sheehan, 2012). However, in the last year or two of his life, he seems to have backtracked a bit. In 1909, he found Lowell’s map of Mercury (published by Lowell in 1896–97 but not actually seen by Schiaparelli till then) “terrifying”, as it showed the planet bizarrely cut up “like a faceted diamond”, while in that same year, when Lowell charged him with carefully examining with an eyeglass the photographic images Slipher had obtained on an expedition to Chile in 1907, and allegedly showing canals, Schiaparelli could only see (with his one good eye) scratches and alignments of the grains of the emulsion. (McKim & Sheehan, 2009) In the end, we cannot know his final view, and when he died on 1910 July 4, he took his secret with him to the grave. In addition to Schiaparelli’s historic importance as a Mars observer, some of his observations are still useful to Mars researchers today. When Green and Schiaparelli first began their observations in 1877, Mars’s albedo features were faint. We now know why. In early August the planet was recovering from the effects of a global dust storm, the earliest so far documented. It was only witnessed by the French astronomer E. L. Trouvelot who had begun observing as early as April, some five months before opposition. Trouvelot’s observations of the event were located only in 2009 (McKim et al., 2009). Following this planetary-scale event, there were further, smaller-scale obscurations. Schiaparelli wrote that “There can be no doubt that Protei Regio was twice

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Fig. 2.3 A dust storm along Valles Marineris recorded by Schiaparelli on 1877 September 26 (right-hand drawing) appears as a short bright streak left of centre running east–west. South is uppermost (Schiaparelli 1878)

covered by a light veil, on September 26 and October 4, and twice became clear again.” In fact this dust activity was part of a larger event lasting from September 24 till October 10. (McKim, 1999:21–24) Schiaparelli’s drawing of September 26 shows a light streak over Protei Regio, but today we would recognise it as dust running along the eastern part of the great canyon system of the Valles Marineris (Fig. 2.3). Despite this success, Schiaparelli was mistaken in inferring the persistence of a large dust veil over certain areas that in reality were intrinsically lacking in detail. At the next opposition, 1879, Schiaparelli discovered on a single night a bright patch in the northern mid-latitudes which he called Nix Olympica (‘snow of Olympus’). We now know that he had discovered something momentous: the giant 27 km high Olympus Mons volcano. At certain seasons an orographic cloud forms above the summit and is visible telescopically as a white patch in the afternoon and evening, though this is not what Schiaparelli was seeing. Instead, he observed a brightening that becomes noticeable a week or so either side of opposition date. This ‘opposition effect’ has been well seen at other oppositions. In his observations in the 1880s, when the northern hemisphere was better presented to view than the southern, there were other discoveries. Schiaparelli was the first to spot a fine rift transecting the shrinking north cap. He also observed that as the cap shrank it tended to fragment. Some outliers were left behind, and to this day we preserve his names for two of them, Olympia and Cecropia. They act as useful seasonal indicators. Schiaparelli also made the first reliable micrometrical measures of the diameters of the polar caps, which can be compared to modern recession data to look for evidence of changes in Martian climate.

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In summary, Schiaparelli deserves great credit for initiating the accurate mapping of the principal albedo markings and introducing the system of nomenclature which is the basis of that now in use. On the negative side, the ‘canals’ led to a long-running, contentious, and in the end rather sterile debate about the nature of the Martian markings that would lead most professional astronomers to abandon planetary astronomy until the 1950s. However, this was certainly not Schiaparelli’s fault, and there were other reasons involved, notably the introduction of large instruments, advances in modern Physics, and the increasing absorption of astronomers in the vast problems of stellar and nebular astronomy. In any event, Mars remained a favourite object of amateurs. Publication of the Mars observations was done through the Memoria (Memoirs) of the Royal Lincei Academy. In 1929, Italian publisher Ulrico Hoepli commenced a lavish edition of the collected works, in large-format volumes. Later still, in 1968, the US-based Johnson Reprint Company would reprint the whole series in a series of eleven small-format volumes. Nowadays even the reprint series is a rarity. We show the actual appearance of these publications in Fig. 2.4. Schiaparelli got his 1877–78 work into print quickly, in (1878), both in the Memoir and in an abbreviated published summary. The 1879–80 data appeared in 1882, but the 1881–82 results were not published till 1886. As time went on the delay increased so that his work had less impact upon contemporary discussions, and in addition, by 1890 pollution and deteriorating observing conditions in the city of Milan—as well as serious problems with his eyesight—led him to abandon any plans to publish later observations. From 1890 onward he effectively gave up planetary work (though he still continued to make double star measurements). Schiaparelli’s failing eyesight is probably to be blamed upon another line of planetary work he began pursuing in 1881–82 and continued until 1889: the daylight observation of the difficult and hitherto much neglected planet Mercury. To François Terby in 1895 he admitted that he was troubled by “a diminution of the sensibility to weak illuminations; I attribute this to the observations of Mercury near the sun carried out from 1882 to 1890. I have entirely abandoned this dangerous kind of observations.” In contrast to previous observers of the innermost planet, who had exclusively studied it during the short twilight periods when it had to be viewed through the densest layers of the Earth’s atmosphere, Schiaparelli hit upon the idea of making his observations during broad daylight. The critical question was whether the markings were definite enough to withstand the loss of contrast. Initial experiments in 1881 June showed that they were, and so, at the end of 1882 January, he began a serious study of the planet. The air over Milan was turbulent during the summer, but in winter it was often “pure and calm,” and observations at any time during the day were feasible. Using the 22 cm Merz refractor with a magnification of 200×, Schiaparelli set out to scrutinize a tiny pale-rose orb a little smaller than the Moon viewed with the naked eye. Markings were almost always present, he found, in the form of “extremely delicate streaks,” but of such low contrast they disappeared whenever haze or a layer of cirrus clouds were present.

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Fig. 2.4 From left to right, one of Schiaparelli’s Mars Memoirs, volume I of his collected works Le Opere Di G. V. Schiaparelli, published by Ulrico Hoepli in 1929, and a volume from the Johnson Reprint Company collection of 1968. Credit R. J. McKim’s collection

Observing in daylight, he was able to follow the planet for several hours at a time, and immediately was able to show that the 24-h rotation favoured by astronomers since J. H. Schroeter was mistaken. On February 6, upon the nearly dichotomized disk he made out a “large system of spots” which appeared like the numeral 5 (and whose parts he indicated with the letters w a b k i). This figure of 5 made a profound impression on him and haunted him whenever Mercury ran east of the Sun (as it

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Fig. 2.5 Schiaparelli’s view of Mercury, 1882 February 6, Central Meridian 85.6°, compared to a blurred WinJUPOS simulation for the same date and longitude. The ‘figure of 5’ which made such an impression on the great Italian astronomer is clearly evident in the simulation. South is uppermost. Credits INAF-Osservatorio Astronomico di Brera, Milan, and John Boudreau

did once more in May, when he again seemed to make out the figure of 5). On the other hand, whenever the planet was in western elongation he seemed to find a prominent dark patch which he labelled q. See Fig. 2.5 for some original sketches and simulations from the modern map. Schiaparelli made the bulk of his 150 drawings of the planet with the 22 cm Merz in 1882–83. As early as 1882 October, he had become sure that the rotation period was the same as that of revolution: 87.9 days. However, he held back from publishing, because the markings seemed to be strangely variable over time. At first he could not explain this. Eventually, after further observations, including with the 22 cm Merz and a larger telescope, a 49 cm Merz-Repsold refractor which was installed at Brera in 1886 (Fig. 2.1), he decided that obscuration by Mercurian clouds was responsible, and that the planet had an atmosphere that was even more substantial than that of Mars. At last, in 1889, he published his great Memoir on the planet, which included not only his arguments about the rotation and clouds but a map that united the features on the ‘figure of 5’ hemisphere with those on the ‘q’ hemisphere. See Fig. 2.6. Later astronomers were so in awe of Schiaparelli’s reputation and convinced by his study that his results, including even the clouds, were confirmed many times by later astronomers (including most notably E. M. Antoniadi). Not until 1965 did the true picture become clear, when radio astronomers discovered the actual period: 58.65 days. In retrospect, it seems that certain faint and diffuse Mercurian markings resemble each other, and after his initial impressions were established, at later elongations Schiaparelli mistakenly thought he was seeing the same region when he was in fact observing a similar marking located in the other hemisphere. This is made clear in the cylindrical projections based on Schiaparelli’s drawings and recent CCD imagery using the correct 58.65 day rotation period, in Fig. 2.7.

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Fig. 2.6 Schiaparelli’s famous planisphere, based on his belief that the rotation period was the same as that of revolution, 88 days, published in 1889. The prominent feature q is on the left of the centre line, and the figure of 5 on the right. South is uppermost. (G. V. Schiaparelli, ’Sulla rotazione di Mercurio’, Astronomische Nachrichten no. 2944, vol. 123, issue 16, 1889)

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Fig. 2.7 Cylindrical projections of the albedo markings of Mercury: (top), based upon Schiaparelli’s sketches, but reinterpreted using the correct rotation period of 58.65 days, and (below) based upon CCD imagery by John Boudreau using a 279 mm Schmidt-Cassegrain telescope between 2007 and 2009. South is uppermost. Credits W. P. Sheehan and John Boudreau

Schiaparelli also observed Venus in the hope of determining its rotation period. The markings on Venus are vague, nebulous and poorly defined, and so the results were tentative at best. As with Mercury, he favoured a long rotation period, and it is a measure of his standing as an astronomer that the very first paper to appear in the first number of the Journal of the British Astronomical Association, published in 1890 October, was a review of his work on the rotation periods of both Mercury and Venus by the historian Agnes M. Clerke. His conclusions would be perpetuated by Lowell. They were by chance partly correct. The surface of the planet rotates upon its axis in 243 days (retrograde) compared to the sidereal period of 224.7 days. But the atmospheric markings exhibit a superrotation in just four days, showing that apart from the lighter regions seen by them at the cusps, they could not really have been observing objective shadings upon the Venusian disk. Schiaparelli was the titanic figure of planetary astronomy in the last quarter of the nineteenth century, and though he made mistakes, he needs to be judged in terms of the times in which he worked. Later, with the introduction of photography, his visual methods came to be seen as unreliable and out of date, and observers with

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Fig. 2.8 A globe of Mars produced by the United States Geological Survey Astrogeology branch in Flagstaff, Arizona, from Viking Orbiter imagery. The giant crater named Schiaparelli is located just left of centre. Credit USGS

larger telescopes such as Antoniadi showed that some of his findings could only be accepted with qualifications (though even Antoniadi accepted Schiaparelli’s Mercury results). His influence on culture was perhaps even greater than that on astronomy. We recall that Mars is the God of War, a fact which ultimately would lead to a particular genre of science fiction books and films, where the legacy of Schiaparelli and Lowell reigned supreme. The fantasy Mars of John Carter and Dejah Thoris created by Edgar Rice Burroughs was a world of classical canals, deserts, lush oases and Martian warlords, and still resonates to a certain extent today. The real Mars has turned out to be very different to what they imagined but even there Schiaparelli’s presence is noted—in the nomenclature still used which is based on the ‘euphonious names’ he first introduced, and in a giant crater located near the equator of Mars which has been named Schiaparelli (Fig. 2.8).

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References Ferrari, A. (2011). Between two Halley’s comet visits. Memorie Della Societa Astronomica Italiana (journal of the Italian Astronomical Society), 82(2), 232–239. McKim, R. J., Sheehan, W. P., & Rosenfield, R. (2009). Etienne Leopold Trouvelot and the planetencircling martian dust storm of 1877. Journal of the British Astronomical Association, 119(6), 349–350. McKim, R. J., & Sheehan, W. P. (2009). Schiaparelli’s final words about Mars. Journal of the British Astronomical Association, 119(5), 255–261. McKim, R. J. (1999). Telescopic Martian Dust Storms: A Narrative and Catalogue. Memoirs of the British Astronomical Association, 44. Putnam, J., & Sheehan, W. (2012). A Complicated Relationship: An introduction to the correspondence between Percival Lowell and Giovanni Schiaparelli. Journal of Astronomical History and Heritage, 24(2), 170–227. Schiaparelli, G. V. (1878). Osservazioni astronomiche e fisiche sull’asse di rotazione e sulla topografia del pianeta Marte. Memoria Reale Accademia dei Lincei, Anno CCLXXV (1877–78). Roma: Salviucci. Schiaparelli, G. V. (1996). Astronomical and Physical Observations of the Axis of Rotation and the Topography of Mars, First Memoir, 1877–1878. English translation of Schiaparelli (1878) by William Sheehan. San Francisco: Association of Lunar and Planetary Observers, A.L.P.O. Monograph no. 5. Sheehan, W. P. (1988). Planets & Perception: Telescopic Views and Interpretations, 1609–1909. The University of Arizona Press.

Chapter 3

Planetary and Cometary Astronomy at the Collegio Romano Aldo Altamore and Francesco Poppi

Abstract Jesuit astronomers working at the Collegio Romano Observatory have made many contributions in the field of planetary astronomy: De Vico and Dumouchel studied Halley’s comet, while Secchi was a pioneer in cometary spectroscopy, studying the surface of the Moon, Saturn’s shape, and Mars’ surface; he discovered a comet in 1853, and in 1869 he was the first to observe the spectrum of Uranus.

Introduction The Collegio Romano can be considered one of the places where modern science was born. Since its foundation,1 astronomical observations have been carried out there, first with the naked eye and later with optical instruments. The first telescopic planetary observations date back to 1611, when Cardinal Roberto Bellarmino (1542–1621) asked his Jesuit confreres to verify Galileo’s observations. Under the supervision of Christopher Clavius (1538–1612), they built a Galilean telescope and confirmed the conclusions of the Pisan scientist. However, the establishment of a true observatory at the College dates back to the year 1787, when Abbot Giuseppe Calandrelli (1749–1827) built a tower in the southeast corner of the roof of the palace to house astronomical instrumentation (Fig. 3.1). 1 The Collegio Romano was established by Ignatius of Loyola (1491–1556) a few years after the foundation of the Society of Jesus for the purpose of training young people from elementary school to university. At the order of Pope Gregorio XIII, between 1582 and 1584 a large building was erected to host the sessions; after the fall of Rome in 1870, it was expropriated by the Italian State. Its cultural tradition was later passed on to the Università Gregoriana (Monaco, 2000; Maffeo, 2012).

A. Altamore Specola Vaticana and INAF-Osservatorio Astronomico di Roma, Rome, Italy e-mail: [email protected] F. Poppi (B) INAF-Osservatorio Astronomico di Roma, Rome, Italy e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_3

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The tower still exists today and is even now used for meteorological observations with the instrumentation placed on its top. Inside the tower there is a sundial, and in the same room there are two marble commemorative plaques: one concerns the construction of the tower in 1787, the other one the visit of Pope Pius VII together with the King of Sardinia, Vittorio Emanuele I, on the occasion of the solar eclipse of 11 February 1804 (Buffoni et al., 2001). Calandrelli was called to the chair of mathematics in 1773, when Pope Clemens XIV ordered the suppression of the Society of Jesus and entrusted the College to the secular clergy. After the reconstitution of the Society of Jesus in 1824, the directorship of the astronomical observatory was held first by Etienne Dumouchel (1773–1840), who was director until 1838, and then by Francesco De Vico (1805–1848) from 1839 to 1848. Dumouchel strove to equip the Observatory with new instruments; in particular, thanks to the financial support of the General Superior of the Society of Jesus Luigi Fortis (1749–1829), in 1825 he purchased a Cauchoix achromatic refractor telescope of excellent construction (Fig. 3.2). This instrument had a long operational life. After Secchi became director in 1850, it was installed on a new equatorial mount and moved to the new Observatory of the Collegio Romano, built by Secchi above the church of St. Ignatius. It was later used

Fig. 3.1 A gravure of the Collegio Romano with the Calandrelli Tower (G. Calandrelli and A. Conti, Opuscoli astronomici, 1803)

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Fig. 3.2 The Cauchoix telescope with the old altazimuth mounting (De Vico, 1840c)

by Pietro Tacchini (1838–1905) and Giuseppe Armellini (1887–1958) until it was finally moved to the Monte Mario Observatory, where it was still used for both scientific and educational purposes until the end of the 1980s. In 1851, under the direction of Angelo Secchi (1818–1878), the Observatory was completely renewed (Secchi, 1856a). Only the meteorological instruments remained at the Calandrelli Tower, while the astronomical instruments, especially those dedicated to astrophysics studies, were located in the new rooms and installed above the sturdy pillars that had been designed to support a large dome that was never built. After Secchi’s death, the Observatory passed to the Italian State and was annexed to the newly established Ufficio Centrale di Meteorologia, directed by Pietro Tacchini. Astronomical observations continued until the early 1900s under the guidance of Tacchini himself and Elia Millosevich (1848–1919). Finally, in 1923 the Observatory of the Collegio Romano was merged with the Observatory of the Campidoglio under the direction of Giuseppe Armellini and became the founding nucleus of the Astronomical Observatory of Rome, whose headquarters were located in the ancient Villa Mellini in Monte Mario in 1938.

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Planetary Observations in Italy Before the Nineteenth Century After the observations made at the time of Galileo, the Jesuits continued to study the Solar System, not only at the Collegio Romano. The Jesuit Giovanni Battista Riccioli (1598–1671), who lived in Bologna, produced a detailed map of the visible part of the Moon and created the nomenclature of craters and seas that is still used today. He was also among the first astronomers to deepen the study of the libration of the Moon, manifested by an oscillation of the visible lunar disk. This means that the visible surface of our satellite during the year is greater than half of its total surface even if the Moon turns the same face to the Earth. These studies were carried out with the contribution of another Jesuit, Francesco Grimaldi (1618–1663), who is also famous for the discovery of light diffraction (Fig. 3.3). In addition, Riccioli observed and described the five planets known at the time (Mercury, Venus, Mars, Jupiter and Saturn) and noted the variations in the shape and position of Jupiter’s bands. Francesco Bianchini (1662–1729), maker of the famous meridian line in Santa Maria degli Angeli church in Rome, made systematic observations of Venus. He determined its rotation period to be 24 days, which is very far from the real value (Bianchini, 1728). Indeed, due to the dense atmosphere that covers the planet’s surface, the period of rotation of Venus remained an enigma until the twentieth century, when it was possible to perform radar observations in frequencies where the planet’s atmosphere is transparent. Bianchini drew a map of the planet and constructed a globe of Venus, which is now kept at the Museo della Specola in Bologna. His observations were conducted from various places in Rome and from Albano using telescopes made by Giuseppe Campani (1635–1715) with a focal length of more than 10 m. Campani had his optics laboratory in the centre of Rome, not far from the Collegio Romano, and made planetary observations by himself, in particular of Saturn, drawing the unequivocal shape of the rings (Campani, 1664). Eustachio Divini (1610–1685) is the other famous instrument maker operating in Rome in the seventeenth century. His telescopes were provided with wooden tubes whose focal length could exceed 15 m; with them he observed the Moon, Jupiter and Saturn and those of their satellites that were known at the time (Divini, 1660). The Jesuit Gille François de Cottignies (1630–1689) observed the atmosphere of Jupiter, as well as the great comets of 1664, 1665 and 1668. Assisted by Brother Salvatore Serra, de Cottignies observed Mars from 27 to 30 March 1666 with a telescope by Divini of “25 palms”2 and with a second telescope of “45 palms”. By measuring the changes in the position of some formations on the Martian surface, 2

25 palms of focal length correspond to approximately 5.6 m. It is probably one of the long focal length telescopes currently on display at the Astronomical and Copernican Museum of the INAF-Astronomical Observatory in Rome.

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Fig. 3.3 Drawing of the Moon by Giovanni Battista Riccioli and Francesco Grimaldi (Riccioli, 1665)

they hypothesized a rotation period around the axis of the planet of approximately 13 h (Cassini, 1666), which is very far from the true rate.3 Giuseppe Maria Asclepi (1706–1776) observed the 1761 transit of Venus across the Solar disk from the Collegio Romano. He also measured the diameters of Venus and Mars, and conducted observations of Mercury and the comet of 1769 (Asclepi, 1761, 1765, 1767, 1770). Finally, it is worth mentioning that Ruggero Giuseppe Boscovich (1711–1787) SJ observed the transit of Mercury in 1737 in Rome. He laid the foundations of geodesy through the first measurement of the geodetic base along the Appia Antica. His work was interrupted because of the Napoleonic occupation and subsequently resumed by 3

“Anno 1666 die 30 Martii hor. 2 n.s. typus Martis cum insignibus maculis Romae visis primum a DD. fratribus Salvatore ed Francisco de Serris tubo Eustachii Divini palmorum 25., ac subinde 60. a die 24. Martii ad 30., qua die in aedibus IlI.mi D. Caesarii Giorii hora praedicta, et ipsomet Illmo D. describente tub. pal. 45. apparuit, ut hic exprimitur, inverso modo nigriore inter alias existente macula orientali, pro situs observata variatione ejusdem planetae circa primum axem revoluzionis periodum indicatura, horis nempe circiter 13” (books.google.it/books?id = qmZPeL_r9i4C at the Biblioteca Casanatense).

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Secchi in 1854–55, as reported in a plaque placed along the ancient street near Capo di Bove (Aebischer, 2012).

Comets’ Observations at the Collegio Romano Observatory Giuseppe Calandrelli and his assistant Andrea Conti (1777–1840) described the observations of planets and other celestial bodies in the eight volumes of Opuscoli astronomici of the Collegio Romano published from 1803 to 1824. They calculated the orbits of planets and comets and provided detailed tables of the parallax of the Moon. Later, in 1816 they were joined by Canon Giacomo Ricchebach (1776–1841). A few decades later, Angelo Secchi declared that the scientific value of the work of these astronomers far exceeded the poverty of the instruments they had used at the Collegio Romano. In the Opuscoli astronomici of the year 1808, Calandrelli reported the observations of the comet of September 1807. In the same issue Andrea Conti published the orbital elements of the comet (Calandrelli, 1808; Conti, 1808).4 Similarly, the 1813 issue reports the observations and orbital elements of the great comet that appeared in 1811 (Calandrelli, 1813; Conti, 1813). This comet was visible to the naked eye for approximately 250 days and was mentioned by Lev Tolstoj in War and Peace. Etienne Dumouchel observed the return of Halley’s comet with the Cauchoix refractor on 5 August 1835, and he immediately reported it in the periodical Astronomische Nachrichte (Dumouchel, 1835). The credit for this discovery is attributed to his young assistant Francesco De Vico (1836), who calculated the comet’s orbit on the basis of previous apparitions and identified its expected position, thus allowing its discovery long before other astronomers noticed it (Secchi, 1851b). De Vico continued to carry out cometary observations at the Collegio Romano Observatory during his directorate. We just mention the comet of July 1839, which was discovered during the collection of data concerning the constitution of nebulae: as written in the Memorie del Collegio Romano published on 31 January 1840, the observations were made with the Cauchoix telescope with the assistants Luca Boccabianca (1810–1875) SJ and Benedetto Sestini (1816–1890) SJ (De Vico, 1840a). In total, De Vico was given priority in the discovery of seven comets observed at the Collegio Romano in the years from 1839 to 1847, and for his discoveries he was awarded by the King of Denmark. Questions about the physical structure of the Solar System became increasingly interesting during the nineteenth century, and they drove the attention of astronomers to comets because cometary orbits were used to determine the masses of the planets with no satellites and to understand the composition of the comets themselves. Angelo Secchi, who succeeded De Vico in the direction of the Observatory, reported in the Astronomische Nachrichte on 25 August 1852 the observation of 4

This comet was also observed in Palermo by Niccolò Cacciatore (1770–1841) (Cacciatore, 1808; Chinnici, 2015).

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the return of Comet Biela, which split into two parts during the previous passage of 1846 (Chinnici, 2019; Secchi, 1852b, 1856e). In the same issue of the German periodical, Secchi communicated data on the asteroid Melpomene observed at the Collegio Romano (Secchi, 1852a), which had been discovered just over a month earlier by the English astronomer John Russell Hind (1823–1895). In 1853 Secchi himself discovered a new comet (Chinnici, 2019; Secchi, 1856f). Secchi mentions observations of numerous other comets between the years 1856 and 1862 (Secchi, 1856h, 1863a) and then again in 1874, carried out together with his assistant Enrico Cappelletti (1831–1899) SJ. Cappelletti was a good draftsman, and his contribution was of great importance for sketching the drawings of comets and other celestial objects (we will see later in particular those of Mars) that Secchi observed. Extensive studies were made for the Comet of 1861, in particular on its nucleus, to show that the tail jets increased as the distance from the Sun decreased (Fig. 3.4). Secchi was also interested in cometary spectra, starting from 1866, when he observed

Fig. 3.4 Comet observed at the Collegio Romano Observatory in 1861 (INAF-Osservatorio Astronomico di Roma, Historical Archive)

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the spectrum of Comet Tempel and found that the chemical composition of the comets was different from that of nebulae (Secchi, 1874a). The greatest development on the subject came with Schiaparelli’s discovery of the correlation between comets and shooting stars, to which Secchi gave space on several occasions in the Bullettino he edited (Schiaparelli, 1866). In Secchi’s words, “these meteors moved accordingly with the orbits of comets, so one of two consequences was inevitable, either that comets were clusters of shooting stars, or that comets were large shooting stars that were tied to the orbits of these bodies” (Secchi, 1877).5 Finally, we recall the contribution of Elia Millosevich, who, unlike his predecessors, was more devoted to celestial mechanics than to astrophysics, turning his attention to calculating the orbits of comets and asteroids (Cerulli, 1919). He discovered the asteroids Josephina and Unitas in 1891, and in 1899 he was among the first to calculate the highly eccentric orbit of the asteroid Eros with very high accuracy, showing that the trajectory covered by this asteroid periodically brings it close to Earth. This work, in particular the prediction of the proximity of Eros to the Earth on the occasion of the asteroid’s opposition in 1900, was of great use for a more precise determination of the Solar parallax and, consequently, of the astronomical unit.

Planetary Observations During the Directorates of Giuseppe Calandrelli and Francesco De Vico From the Opuscoli astronomici edited by Giuseppe Calandrelli, we know that Andrea Conti, a friend and pupil of Calandrelli, observed the transit of Mercury on 8 November 1802 from the tower built by Calandrelli himself on the roof of the College (Conti, 1803). Conti wrote that the observations of the phenomenon were disturbed by the frequent passage of clouds. However, he did not lose heart and completed the mathematical study of the phenomenon. In his analysis he also used observational data provided by Giuseppe Cassella (1755–1808), director and founder of the Astronomical Observatory of Naples at the ancient monastery of San Gaudioso in Caponapoli; by the Viennese astronomer Franz de Paula Triesnecker (1745–1817); and by the French Joseph Jérôme Lefrançois de Lalande (1732–1807), who sent him the data taken by Joseph Thulis (1768–1810), director of the Observatory of Marseille. Observations of Uranus and Jupiter on the occasion of their oppositions of 1819 are reported in the Opuscoli astronomici of the year 1822 (Conti, 1822). Conti wrote that the measurements of the position of Uranus were made with the transit instrument and the mural quadrant, and with the transit instrument and the Reichenbach multiplier circle for Jupiter. He used the positions of the fixed stars from Piazzi’s catalogue, published in 1814, as reference points. From them, Conti calculated the times of the 5

“…queste meteore andavano di conseguenza con le orbite delle comete, onde era inevitabile una delle due conseguenze, o che le comete erano ammassi di stelle cadenti, o che le comete erano stelle cadenti maggiori che camminano di conserva con le catene di questi corpuscoli” (Secchi, 1877).

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oppositions of the two planets and proposed new tables of Uranus, with correction of the old tables by Barnaba Oriani (1752–1832) and Jean Battiste Delambre (1749– 1822). Conti was assisted by Ignazio Calandrelli (1792–1866) in calculating the elements of Uranus’ orbit. Ignazio was nephew of Giuseppe Calandrelli and director of the Astronomical Observatory of the Campidoglio after 1848. Ignazio Calandrelli renovated this observatory, obtaining funds from Pio IX for improving the instrumentation, which was increased with an Ertel meridian circle and an equatorial refracting Merz telescope. Back at the Collegio Romano, in the Opuscoli of 1824, we also find tables to calculate the annual parallaxes of Jupiter and Saturn by Conti (Conti, 1824a). In addition, he calculated new tables of Mercury (Conti, 1824b) starting from the data of the planet’s transit over the solar disk, which was observed in November 1822 in Parramatta (New Wales, Australia) by Georg Friedrich Wilhelm Rümker (1832– 1900). We have already mentioned Francesco De Vico in the section dedicated to comets, in particular for his precise calculation of the ephemeris of Halley’s comet, which made it possible to observe the return of the comet at the Collegio Romano in 1835 before any other observers. His skill was not limited to calculation; he was also a keen observer. In 1838 De Vico was able to observe the satellites of Saturn, Mimas and Enceladus with the Cauchoix telescope. From a series of very accurate observations, he calculated the period of revolution of both and the ephemeris of Mimas (De Vico, 1838b). Due to the proximity of these satellites to the planet, only the discoverer William Herschel (1738–1822) had seen them before De Vico did, and that only on a few occasions. De Vico attempted to study the divisions of Saturn’s rings; to facilitate these observations he introduced a small opaque metal sheet into the focus of the eyepiece to hide the planet, whose brightness interfered with seeing the objects closest to it (De Vico 1838a, 1840b, 1842a, 1843a). He tried to measure the supposed eccentricity of the rings with respect to the position of Saturn and to verify the rotation time of the rings themselves, in both cases without success (Fig. 3.5). De Vico and his assistants Clemente Palomba (1819–1891) and Benedetto Sestini conducted numerous observations of Venus with the aim of calculating the rotation period of the planet. However, he was misled by the presence of a dense atmosphere on Venus, which was unknown at the time and did not allow us to observe its surface. In the Memorie del Collegio Romano we find a detailed description of the attempts to see the spots on the surface of Venus and to follow their movements as long as possible, even in broad daylight. Using the Cauchoix telescope with a string micrometer applied on it, he concluded that a full revolution of Venus on its axis occurred in between 23 and 24 h (De Vico, 1840c, 1842b, 1843b). De Vico also wrote that he could not believe that Bianchini had made such a gross mistake by declaring a rotation of 24 days. Today we know that both were wrong; in fact, the rotation period of Venus is very slow, equal to approximately 243 Earth days, and retrograde.

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Fig. 3.5 Saturn and its first satellite observed by Francesco De Vico (De Vico, 1840b)

Planetary Observations During the Directorate of Angelo Secchi When Secchi took over the directorate of the Observatory of the Collegio Romano, he found himself having to work with instruments located in a tall tower that lacked the necessary stability for accurate observations. As previously mentioned, he started the construction of a new observatory located on the pillars of the church of St. Ignatius and commissioned new instrumentation, including the Merz equatorial refractor. The first improvement he made concerned the Cauchoix telescope, which was equipped with a new equatorial mount, making it more suitable for observations of comets and minor planets. Among others, Secchi studied asteroid Massalia (Secchi, 1852c), discovered in September 1852 by Annibale de Gasparis (1819–1892) at the Astronomical Observatory of Capodimonte, and at the same time by the French astronomer Jean Chacornac (1823–1873), who first communicated the discovery, and Polimnia (Secchi, 1856g). It is well known that Secchi was more interested in the study of the physical nature of celestial bodies rather than in their motions, and this is evident in the planetary observations he conducted. From the beginning, his studies included spectroscopic observations of the planets, and these became more extensive from the end of the 1860s (McKim Sheehan, 2021).

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The Moon Photographs The eclectic nature of Secchi’s interests led him to experiment with all kinds of new techniques in astronomical observations, including photography. In fact, together with the pharmacist and photographer Francesco Barelli, in 1858 he created the first photographic atlas of the Moon (Secchi, 1858a, 1858b). Using the wet collodion technique, they obtained eight different detailed images of the satellite during the crescent phases. Moreover, Secchi made an extremely detailed drawing of Crater Copernicus, the result of a study that lasted more than two years starting in 1855 (Secchi, 1856d). Secchi also photographed the planets Jupiter and Saturn: “in the first [Jupiter] the bands, in the second [Saturn] the ring with its shadow were very clear”6 (Secchi, 1858c, 1859b). His photographs of the Moon have survived to our time, but not those of the planets. Secchi tells us that the latter were overexposed. From the exposure times he deduced that the absolute brightness of Jupiter exceeded that of Saturn, which far exceeded that of the Moon, and referring to the latter he ironically noted that his conclusion “may seem strange to those who hear so much praise of [the Moon’s] silvery splendor” (Fig. 3.6).7

Mercury Secchi mentions numerous observations of Mercury. He noticed spots and structures on its surface, but he did not systematically study it, probably due to the difficulty of observing the planet as it is always immersed in twilight (Secchi, 1863b).

Venus With Benedetto Sestini, Secchi observed Venus several times, both on the occasion of its transit in front of the solar disk and during inferior conjunctions. In particular, during the inferior conjunction of 1857, Secchi was convinced that the planet had a dense atmosphere. He also mentioned the presence of possible surface structures, which he believed to be solid. Today we know that in reality the very opaque atmosphere prevents observation of the surface of Venus. At that time one issue was therefore to determine the exact period of rotation of the planet, which remained unanswered until the 1960s, when radar observations in radio wavelengths were able to penetrate the dense atmosphere. 6

“…nel primo si ebbero nettissime le fasce, nel secondo l’anello fino colla sua ombra” (Secchi, 1859c). 7 “…conclusione che potrà parere strana a chi tanto sente decantare l’argenteo suo splendore” (Secchi, 1859c).

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Fig. 3.6 Photograph of the Moon on the 6th day taken by Angelo Secchi and Francesco Barelli (Secchi, 1858a)

Secchi himself realized that some of the features he observed changed their shape and that consequently they could not be associated with the surface of the planet but with its atmosphere. From the observations of the spectral lines, Secchi noticed a certain similarity between the atmospheres of Venus, Mars and the Earth (Secchi, 1874b).

Mars Mars was the planet most continuously observed by Secchi (Secchi, 1856i, 1858c, 1859c, 1863d). In 1859 Secchi published 18 detailed drawings of the red planet

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and two representations of the view of its lower and upper poles (Secchi, 1859a). This was the result of observations carried out from June to August of the previous year, at the time of the opposition of the planet, drawn with great accuracy by the hand of Cappelletti. The result was noteworthy, most likely thanks to the favourable conditions given by the planet’s position in the sky and by the excellent quality of the Merz telescope with a 24-cm aperture and 4.35-m focal length. Several years later, in 1877, Secchi described his work on Mars, writing that “the most important discovery is that of two permanent blue channels between the two great red equatorial continents, which was confirmed by subsequent observations since the planet has been reobserved in recent years almost under the same aspect”.8 (Secchi, 1877). Regarding the polar caps, he went on saying that “their extreme variability was proved; which leads us to believe them to be clusters of clouds rather than snow or ice”.9 He concluded by saying that “many of these latter drawings are unpublished”,10 as if to demonstrate an awareness of the value and uniqueness of his work, or perhaps a certain humility in not considering the result of his observations sufficiently confirmed by other studies (Fig. 3.7). We also know from Secchi’s words that a few of these drawings were sent to Francois Terby (1846–1911), who was also interested in studying the planet. From these drawings and his writings it is possible to note that Secchi observed and documented some Martian sandstorms (McKim, 1999). A significant landmark in the study of this planet in the years to come was the use by Secchi of the word “canali”, which should be translated as “channels”, to indicate the regular structures that seemed to be present on the surface of the planet. This usage anticipated and perhaps generated the great attention towards the red planet that would be unleashed just over a decade, when the word “canali” was taken up by Giovanni Virginio Schiaparelli (1835–1910), who began observing Mars at the Brera Observatory starting in 1877. It is worth remembering the great mutual esteem between the two scientists (Maffeo, 2011), which is well attested by the note written by Schiaparelli in the register of observations of 26 February 1878, the day of the death of Angelo Secchi (Fig. 3.8). Concerning spectroscopic observations, Secchi observed few absorption bands in Mars, and from this he deduced that the Martian atmosphere should be thinner than the atmospheres of the other planets and in particular of the outer giant planets and that its chemical composition is rather similar to that of the Earth’s atmosphere.

8

“…la scoperta più importante è quella di due canali azzurri permanenti tra i due grandi continenti equatoriali di color rosso, che è stata confermata dalle osservazioni posteriori essendosi il pianeta riosservato negli ultimi anni quasi sotto lo stesso aspetto” (Secchi, 1877). 9 “…si provò la loro estrema variabilità; il che fa credere piuttosto ammassi di nubi che di nevi o ghiacci” (Secchi, 1877). 10 “…molte di queste figure ultime sono inedite” (Secchi, 1877).

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Fig. 3.7 Drawing of Mars in colours by Angelo Secchi and Enrico Cappelletti (Osservazioni all’Equatoriale dal 23 giugno 1858 al 24 febbraio 1859, INAF-Osservatorio Astronomico di Roma, Historical Archive, Folder 43, no. 158)

Jupiter Secchi made a large number of drawings of Jupiter and noticed that the planet’s appearance rapidly changed. He was convinced that phenomena similar to our storms occurred in its atmosphere (Fig. 3.9). The Jesuit also studied the satellites of Jupiter and, in particular, their rotation inferred from the observation of spots on their surfaces (Secchi, 1855, 1856c, 1863e, 1874c). Regarding spectroscopic observations (Secchi, 1864), Secchi observed some peculiar absorption lines that only in the twentieth century have been explained to be due to the high-pressure condition of the gas. In addition, the existence of lines of water vapour was highlighted, as their presence was first denied and then confirmed by other astronomers. However, in light of modern knowledge, it is now understood that these bands are due to the Earth’s atmosphere. In general, the outer planets showed very different spectra from that of the Earth’s atmosphere, which led Secchi to believe that the atmospheres of the gas giants were in a primordial stage and composed of unknown gases.

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Fig. 3.8 Pages of register of the observations made by Giovanni Virginio Schiaparelli on 26 February 1878 with the annotation of the death of Angelo Secchi (INAF-Osservatorio Astronomico di Brera, Historical Archive, Fondo “G. V. Schiaparelli”, cart. 491, fasc. 1)

Saturn Saturn was the first planet to be observed by Secchi, as early as 1850 (Secchi, 1851a), initially with the Cauchoix telescope at the old observatory (the Calandrelli Tower) and later in the new observatory with the Merz telescope. He conducted detailed observations of the structure of the rings, revealing their irregularities and confirming the previous observations made by De Vico and other astronomers (Secchi, 1856b, 1856k). In particular, he observed the very thin third ring, in addition to the first two rings already known from the times of Cassini and Campani. Moreover, he was able to see two subtle divisions of the outermost ring. One of these divisions was discovered in Berlin by Johann Franz Encke (1791–1865). From these observations Secchi was convinced that the divisions must be real empty spaces that separate the rings (Secchi, 1856k). Secchi’s hypotheses were confirmed by Étienne Léopold Trouvelot (1827– 1895), who repeated the same observations with large American refractors in the observatories in Cambridge and Washington. This research continued until 1862, at which time the position of the planet was no longer favourable to observations, and perhaps by then Secchi’s interests were directed elsewhere (Secchi, 1863c).

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FIG. 3.9. Drawing of Jupiter dated 23 January 1859 (Osservazioni all’Equatoriale dal 23 giugno 1858 al 24 febbraio 1859, INAF-Osservatorio Astronomico di Roma, Historical Archive, busta 43, n. 158)

Uranus and Neptune The two outer planets were observed several times without any spots or structures on their surface. In 1869 Secchi was the first to observe the spectrum of Uranus, which was very bright and characterized by the presence of two dark bands (Secchi, 1869). The first was located in the green region of the visible spectrum and the second in the violet. The spectrum of the planet also showed a wide empty interval in the yellow region and a weak emission in the red region. Secchi noted differences with respect to the spectra of Jupiter and Saturn, and also with respect to the spectrum of the Sun, from which he deduced that the peculiarities of the spectrum of Uranus, compared to the reflected light of the Sun, had to be introduced by the planet’s atmosphere (Grassi, 2021) (Fig. 3.10).

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Fig. 3.10 The spectrum of Uranus, as observed by Angelo Secchi (Secchi, 1869)

Conclusion As we have seen, the study of planetary astronomy has been a regular part of the work at the Collegio Romano since its foundation, and this has been conducted by Jesuit astronomers and other scholars over the centuries. These activities continued until the beginning of the twentieth century. In fact, planetary observations were carried out by Pietro Tacchini and Elia Millosevich, who took over the Observatory from the Jesuits after the unification of Italy. In 1880 they used the 24-cm aperture Merz refracting telescope to observe Uranus and the minor planets Juno, Ceres, Hebe, Diana and Nemausa (Tacchini, 1880). Later, further observations were made with the new 39-cm aperture Steinheil-Cavignato refractor, which was installed to replace the Merz telescope (Millosevich, 1904). After that time, the study of the planets continued at the Astronomical Observatory of Rome in Monte Mario under the direction of Giuseppe Armellini. His main field of study was celestial mechanics, and therefore his planetary research was of a theoretical nature (Armellini, 1922). In particular, he conducted in-depth studies on the motion of Uranus and the perturbations of Triton, the largest satellite of Neptune, which made him suspect the existence of other satellites. This intuition was later verified in 1948 when a fifth satellite of Uranus (Miranda) was discovered and again in 1949 with the discovery of a second satellite of Neptune (Nereid), both by Gerard Kuiper (1905–1973). Armellini also studied the perturbations of the orbit of Hungaria, an asteroid of the main belt discovered in 1898 by the German astronomer Max Wolf (1863–1932). Lines of research concerning the planets are still active today in the two INAF institutes of the Roman area. At the Astronomical Observatory of Rome, located in Monte Porzio Catone, this activity is focused on the study of the minor bodies of the Solar System, based on the analysis of data collected by telescopes both on the ground and orbiting in space. Since its foundation, the Institute of Astrophysics and Space Planetology, in Frascati, has been the seat of advanced planetary research, both observational and theoretical, which is still ongoing through participation in important space missions. Planetary astronomy is also carried out at the Vatican Observatory, concerning both the observation of planets and the laboratory study of meteoritic materials. The long tradition of planetary research that we have described in this work, together with the astronomical observations that have been conducted since classical antiquity and the founding of stellar astrophysics in the nineteenth century,

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make Rome a unique place in the history of astronomy. For this reason, it would be worthwhile to further enhance the places and testimonies of this history through dissemination among students, young people in general, and the general public. This could happen through the frequent organization of events, encouraging public access to places of astronomical interest in the city and the development of museum structures dedicated to science. Acknowledgements Earnest thanks to director Guy Consolmagno SJ for allowing us to access the volumes kept in the Library of the Vatican Observatory and for the precious work of revising the English text of the present paper.

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Schiaparelli, G.V. (1866). Intorno al corso ed all’origine probabile delle stelle meteoriche, Bullettino Meteorologico dell’Osservatorio del Collegio Romano, vol. 5, n. 10, pp. 97–106. Secchi, A. (1851a). Nuove apparenze dell’anello di Saturno. Annali Di Scienze Matematiche e Fisiche, N., 2, 39–44. Secchi, A. (1851b). Ragguaglio intorno alla vita e ai lavori del p. Francesco De Vico della Compagnia di Gesù. Secchi, A. (1852a). Beobachtungen der Melpomene auf der Sternwarte des Collegio Romano. Astronomische Nachrichten, N., 822, 88. Secchi, A. (1852b). Entdeckung und Beobachtungen eines kleinen Cometen. Astronomische Nachrichten, N., 822, 90. Secchi, A. (1852c). Osservazioni sul pianeta Massalia fatte all’Osservatorio del Collegio Romano all’Equatoriale Cauchoix. Atti Dell’accademia Pontificia De’ Nuovi Lincei, 5, 314. Secchi, A. (1855). Ricerche sopra il pianeta Giove, fatte coll’equatoriale de Merz all’Osservatorio del Collegio Romano durante l’anno 1850. ll Nuovo Cimento, Giornale di Fisca, di Chimica, et delle loro Applicationi, n. 2, p. 351. Secchi, A. (1856a). Descrizione dell’Osservatorio. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 9–24. Secchi, A. (1856b). Osservazioni di Saturno e suoi anelli. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 97–113. Secchi, A. (1856c). Ricerche sopra il pianeta Giove. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 114–117. Secchi, A. (1856d). Selenografia. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 134–135. Secchi, A. (1856e). Cometa di Biela nella sua apparizione del 1852. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 147–149. Secchi, A. (1856f). Cometa del 6 marzo 1853 scoperta all’Osservatorio del Collegio Romano. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 149–150. Secchi, A. (1856g). Osservazioni del Pianeta Polimnia. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, p. 150. Secchi, A. (1856h). Osservazioni della Cometa Donati e Cometa di Bruhns. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, p. 151. Secchi, A. (1856k). Misure di Sturno e suoi anelli. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 152–153. Secchi, A. (1856i). Osservazioni di Marte. Descrizione del Nuovo Osservatorio del Collegio Romano D. C. D. G. e Memoria sui lavori eseguiti dal 1852 a tutto aprile 1856, pp. 154–156. Secchi, A. (1858a). Mappe fotografiche delle principali fasi lunari. Secchi, A. (1858b). Atlas photographique lunaire. Comptes Rendus Hebdomadaires Des Séances De L’academie Des Sciences, 47, 362–364. Secchi, A. (1858c). Études sur la planète Mars. Comptes Rendus Hebdomadaires Des Séances De L’academie Des Sciences, 47, 364–366. Secchi, A. (1859a). Osservazioni di Marte fatte durante l’opposizione del 1858. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 1(3), 17–24. Secchi, A. (1859b). Fotografie lunari e degli altri corpi celesti. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 1(20), 158–160. Secchi, A. (1859c). Quadro fisico del Sistema Solare secondo le più recenti osservazioni. Secchi, A. (1863a). Alcune considerazioni su le tre ultime grandi comete. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 2(2), 18–32.

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Secchi, A. (1863b). Passaggio del pianeta Mercurio avanti al Sole il giorno 12 novembre 1861 osservato alla Specola del Collegio Romano con aggiunta di altre osservazione diverse. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 2(9), 65–71. Secchi, A. (1863c). Osservazioni di Saturno in occasione della disparizione dell’anello negli anni 1861 e 62. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 2(10), 73–76. Secchi, A. (1863d). Osservazioni del pianeta Marte. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 2(10), 76–79. Secchi, A. (1863e). Giove. Memorie Dell’osservatorio Del Collegio Romano, Nuova Serie, 2(10), 79. Secchi, A. (1864). Observations of the spectrum of Jupiter. The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science, 28, 486–488. Secchi, A. (1869). Resultats fournis par l’analyse spectrale de la lumiere d’Uranus, de l’etoile R des Gemeaux, et des taches solaires. Comptes Rendus Hebdomadaires Des Séances De L’academie Des Sciences, 68, 761–765. Secchi, A. (1874a). Sullo spettro della cometa Tempel. Memorie Della Società Degli Spettroscopisti Italiani, 3, 29–30. Secchi, A. (1874b). Sugli spettri prismatici del pianeta Giove e degli altri pianeti. Bullettino Meteorologico Dell’osservatorio Del Collegio Romano, 13(11), 97–99. Secchi, A. (1874c). Giove e satelliti. Memorie Della Società Degli Spettroscopisti Italiani, III, 39. Secchi, A. (1877). L’astronomia in Roma nel pontificato di Pio IX, Rome (cap. III, pp.16–22). Tacchini, P. (1880). Osservazioni di pianeti fatte all’Equatoriale di Merz dell’Osservatorio del Collegio Romano. Astronomische Nachrichten, 97, 187–190.

Chapter 4

Comet Observers in Florence in the Nineteenth Century Simone Bianchi, Daniele Galli, and Antonella Gasperini

Abstract In the nineteenth century, thirteen comets were discovered, and many more were observed, from the city of Florence, Italy. One of the most remarkable discoveries was the great comet Donati (C/1858 L1). This chapter traces the history of the comet-hunters active in Florence (Jean-Louis Pons, Giovan Battista Donati, Wilhelm Tempel), highlighting the transition from classical studies of celestial mechanics to the emerging field of astrophysics. Furthermore, we focus on Donati’s involvement in the controversy about the comet 3/D Biela and the related spread of a hoax: the alleged impact of a comet with the Earth expected (or rather, invented) for 12 August 1872. We conclude that Florence was indeed “the headquarters of comets”, as von Zach hoped for in 1825, but only at national level. The city that boasted the largest number of discoveries of comets in the nineteenth century is, in fact, Marseille.

Jean-Louis Pons The log of comet discoveries in Florence begins with the arrival in the city of the Frenchman Jean-Louis Pons (1761–1831). Pons, the most famous comet hunter of the nineteenth century, had started his career as a keeper at the Marseille Observatory; there, he discovered 20 comets from 1801 to 1819 (in the following, we will consider as discoveries those for which an astronomer was the first recognised observer; for all information on comets, we refer to Kronk, 2003). The same year, he moved to the new (and ephemeral) Specola (Observatory) of Marlia in the Duchy of Lucca, where he discovered 4 comets before the closure of the observatory.

S. Bianchi (B) · D. Galli · A. Gasperini INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy e-mail: [email protected] D. Galli e-mail: [email protected] A. Gasperini e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_4

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Given Pons’ previous records, great were the expectations when, in August 1825, he moved to Florence, summoned by Grand Duke Leopold II to direct the Specola of the Imperial and Royal Museum of Physics and Natural History. Those expectations were not disappointed: in his first month in the capital of Tuscany, Pons discovered the first Florentine comet, C/1825 P1. A few days later, Pons found Comet 2/P Encke, on its second passage after the German astronomer Johann Franz Encke (1791–1865) had identified it as periodic. Encke, however, referred to it as Pons’ comet because the French astronomer first observed it in the passages of 1805 and 1818, when he was still at the Marseille Observatory (Encke, 1820). Pons’ brilliant debut in Florence made the Hungarian baron Franz Xaver von Zach (1754–1832) comment that Florence had “now become the headquarters of comets” (Zach, 1825: 187). Indeed, the astronomer kept a high discovery pace, with 7 new objects found from the city observatory in just two years, from 1825 to 1827; then, his eyesight faded, and he eventually died in 1831.

Giovanni Battista Donati After the death of Pons, the direction of the Specola passed to Giovanni Battista Amici (1786–1863), an internationally renowned instrument maker from Modena. In the first twenty years of Amici’s direction, astronomical observations were sporadic and essentially devoted to testing his instruments. However, some comet observations are also reported in this period, including those of comet 1P/Halley during its 1835 passage (Arago, 1855: 372, 395–396). More assiduous observations resumed only in 1852, when the young Pisan Giovanni Battista Donati (1826–1873) became an apprentice at the Specola.

First Discoveries and Studies Donati found his first comet, C/1854 R1, in September 1854; the object, however, had already been discovered a few days earlier. Nevertheless, Donati was rewarded for his efforts and was appointed assistant (aiuto) astronomer a month later. He did not have to wait long for his first discovery; indeed, in June 1855, he was the first to observe C/1855 L1. In addition to searches and observations of comets, Donati was trained in the calculation of their orbits by Ottaviano Fabrizio Mossotti (1791–1863), his former professor of celestial mechanics at the University of Pisa. In these early years, the young astronomer undertook the long and difficult calculations of the orbit of the short-perihelion (“sungrazing”) comet, which had appeared extended and very bright in 1843 (C/1843 D1; Fig. 4.1). The goal was to find similarities between its orbit

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Fig. 4.1 The great comet of 1843, seen in Paris on the night of 19 March (Guillemin, 1875; Source archive.org)

and those of other objects observed in the past, thus identifying a new periodic comet. Even though the orbits he derived for the comet were never published, Donati eventually became very skilled in these calculations: he was said to be able to compute an orbit in just four hours, when it usually took thrice as long (Galli et al., 2013).

Donati’s Comet C/1858 L1 At 10 p.m. on 2 June 1858, Donati discovered his third comet, C/1858 L1 (Fig. 4.2). Observed through the main telescope of the Specola, equipped with one of the famous objectives built by Amici, the comet “appeared as a small nebulous spot with a diameter of about 3’, with uniform light over its entire extension” (Donati, 1866b). As anticipated by its discoverer on the basis of preliminary orbit calculations, the comet grew rapidly in brightness, becoming a naked-eye object in the first days of September. By the end of September, the comet had developed a tail that reached a length of 30 degrees. After passing perihelion on 30 September, the comet became a truly spectacular sight by the first days of October, when its head transited near the bright star Arcturus. The length of its elegantly curved, feathery-like tail reached approximately 40 degrees, with a width of approximately 10–16°. After October 10,

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the comet moved away from Earth, and its brightness slowly decreased. The direction of the tail, initially perpendicular to the horizon, became almost horizontal, gradually disappearing from view. From early November, the comet was no longer visible to the naked eye. It was last seen in the Southern Hemisphere by Carlos W. Moesta (1825–1884) at the National Observatory of Santiago, Chile, in March 1859.

Fig. 4.2 Drawings of comet C/1858 L1 by Donati (Annuario, 1859)

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Donati’s comet, as it became known, was one of the most spectacular astronomical events of the nineteenth century, covered in newspapers and illustrated magazines, and admired with awe (or fear) by crowds from all over the world: “it described an immense arc that occupied the entire vault of the sky from west to north–east. It is impossible to describe the marvelous effect that its sight produced. Every evening and until late in the day the population came in crowds […] to admire it in all its majesty from the nucleus to the end of the tail” (Cesana, 1890). “The bridges of Florence were always crowded with people contemplating this extraordinary phenomenon. In all the countryside, nobody talked about anything else, not even the old folks remembering a comet so large and so full of splendor. It seemed that it didn’t want to leave, and it lasted a long time to slowly fade away until it disappeared” (Covoni Girolami, 1981). Testimonies of the passage of the comet are also found in the pages of poets and writers, including Dickens, Hardy, Hawthorne, and Tennyson. In England, the event inspired paintings and watercolors by famous artists and amateur painters, where the comet is inserted in countryside landscapes as a delicate background element (Fig. 4.3) or in nocturnal scenes (Fig. 4.4) as a presence of mysterious symbolic meaning (Gasperini, Galli & Nenzi, 2011a, 2011b). Discovered in the golden age of great geographical expeditions, Donati’s comet was observed in wild and remote lands by famous explorers and simple travelers who recorded the reactions—generally of fear—of indigenous peoples at the sight of the mysterious celestial visitor. C/1858 L1 was the first comet to be photographed: by the American astronomer George P. Bond (1825–1865) at the Great Refractor of Harvard College Observatory on 28 September and by the English commercial artist William Usherwood (1821– 1915) with a portrait camera around the same date. While Bond’s original plate is still kept in Harvard College’s archives, Usherwood’s original plate and the copy sent by him to Bond have been lost (Pasachoff et al., 1996). In 1862, Bond published a scholarly researched monographic study, beautifully illustrated by 51 engravings, of the telescopic and naked-eye appearance of the head and tail of Donati’s comet, which was awarded the gold medal of the Royal Astronomical Society in 1865. Some of the plates in Bond’s monography showed the curved dust tail of the comet flanked by two thin straight plasma tails, features often included in many later popular illustrations of the comet even though extremely difficult to discern under normal sky conditions. The orbit of Donati’s comet computed by Hill (1866) resulted in a high-eccentricity ellipse with a large semimajor axis and a long period of approximately 1950 yr, not far from the most recent computer-assisted analysis of all available data (1927.22 yr, Branham, 2014). A letter of congratulations sent to Donati on 19 October 1858 by the French astronomer Urbain Le Verrier (1811–1877) foretells auspicious consequences for the exceptional discovery: “No one more than me has applauded a success that your previous works have well deserved. In addition, if it is true, as I have been assured, that these circumstances have attracted the attention of your government to you, it will be justice” (Historical Archives of the Arcetri Observatory, Fondo Donati).

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Fig. 4.3 Donati’s Comet observed from Markree Castle, Collooney, Ireland, chromolithograph (E. J. Cooper, Observations of Donati’s Comet made at Markree Observatory, Dublin, s.d.)

Fig. 4.4 Gabriel Loppé (1825–1913), La comète de Donati de 1858, oil painting on canvas (Musée d’Annecy)

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Indeed, in September 1858, Donati was appointed adjunct-astronomer; at the end of 1859, on the eve of the unification of Tuscany to the new Kingdom of Italy, he became professor of astronomy and director of Florence Observatory.

From Celestial Mechanics to Spectroscopy As a director, Donati still followed his interest in comets, even though he was progressively more and more involved in other activities, such as the foundation of a workshop of scientific instruments (Bianchi et al., 2016) and the project of a new observatory to be built on the hill of Arcetri, a better location for astronomy than the old Specola (Bianchi, 2020b). The astronomer continued routine observations and searches for new comets, discovering a couple more objects in 1864, leading to a total bounty of five. One of these, C/1864 O1, was codiscovered together with Specola’s computer Carlo Toussaint (1842–1866). Indeed, young assistants helped Donati in observations: another comet, 109P/1862 O1, was found during an absence of Donati by Toussaint and the assistant astronomer Antonio Pacinotti (1841–1912), who later moved to Physics and was one of the developers of the dynamo; however, the comet had already been discovered earlier. In 1864, Donati announced the discovery of a few manuscripts by the Renaissance geographer Paolo dal Pozzo Toscanelli (1397–1482) in Florence’s National Library; they contained detailed observations of the path of five comets that appeared between 1433 and 1472, including Halley’s comet during the 1456 passage. Donati started to study these manuscripts, probably with the same intent as for his calculations of the orbit of C/1843 D1, i.e., to identify new periodic comets; however, he then abandoned the project and a detailed analysis was published much later (Celoria, 1921). The breadth of Donati’s interests, however, went beyond classical astronomy and celestial mechanics. Indeed, the astronomer is considered among the pioneers of astrophysics, being among the first to observe the spectra of stars and having shown the dependence of the spectra on the stellar color. In 1864, Donati directed the same spectroscope he used for his stellar observations towards comet C/1864 N1, recording the first spectrum of a comet. The observed spectrum presented, however, a completely different aspect from stellar spectra, being made up of three large luminous bands separated by dark areas in the region that goes roughly from blue to green in the solar spectrum (Fig. 4.5). Shortly after Donati’s discovery, the British astronomer William Huggins (1824–1910) noted the close similarity of cometary spectra with the flame spectrum of some hydrocarbons, in particular of acetylene. Only in the 1920s were the bright bands dominating the visual spectrum of comets correctly identified as the emission of the C2 molecule produced by the photodissociation of acetylene and other hydrocarbons present on the comet’s surface (Galli et al., 2016).

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Fig. 4.5 The three bands in the spectrum of C/1864 N1, in a drawing by Donati conserved in the Historical Archive of the Arcetri Observatory (Fondo Donati). It is probably a sketch for the illustration published in Donati (1864)

Biela’s Comet and the End of the World in 1872 As an expert on comets, Donati was involved in some scientific discussions on the fate of comet 3D/Biela. Discussions originated from the spread of a hoax, the alleged impact of a comet with the Earth expected (or rather invented) for 12 August 1872.

The True Comet Biela’s was the third comet recognised as periodic; it takes its name from the Austrian baron Wilhelm von Biela (1782–1856), who first observed it in its 1826 passage and was among the first to compute its elliptical orbit. It was soon recognised that the comet had already been observed in two previous passages, including that of 1805, when it was discovered by Pons in Marseille. Thanks to predictions made, among others, by the director of the Padua Observatory Giovanni Santini (1787–1877), the comet, with a period of approximately 6¾ years, was recovered at the end of September 1832. The calculations showed

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that the comet’s path crossed the plane of the ecliptic at a point very close to the Earth’s orbit. Even if astronomers specified that the comet would have reached that point on 29 October 1832, while the Earth would have arrived a month later, on 30 November (Arago, 1855; Olbers, 1828), some concern arose due to the fear of the comet’s collision with our planet: comets continued to frighten the population, no more because of superstition and fear of the unknown, but for misunderstood (or presumed) scientific predictions. The comet was not seen on its 1839 return due to unfavorable observation conditions: on the days when it would have been visible from Earth, it was too close to the sun. At the next passage, the comet was recovered on 26 November 1845 by the director of the Observatory of the Roman College, Francesco de Vico S. J. (1805–1848), again on the basis of calculations by Santini. De Vico was another very skilled comet hunter, with performances similar to those of Pons, having discovered 6 comets in 2 years, between 1844 and 1846. From mid-January 1846, the comet was seen divided into two parts of different brightness, separated by a gradually increasing distance; in early spring, the two nuclei became too weak to be observed. From position measurements, a few astronomers calculated the orbits of both nuclei: among them, the director of the Geneva Observatory Émile Plantamour (1815–1882). Again, using ephemerides computed by Santini, Angelo Secchi S. J. (1818– 1878), de Vico’s successor as director of the Roman College Observatory, found the brightest of the comet’s nuclei on 26 August 1852 and the other on 16 September. The apparent distance between the two parts, which remained visible only until the end of the month, had become approximately 30’ (Fig. 4.6). New calculations predicted unfavorable observing conditions for the following passage, that of 1859; the 1866 passage, instead, would have been decidedly more propitious. For the 1866 return, the aged Santini delegated the calculation of the ephemeris to his assistant Jacopo Michez (1839–1873) (Santini, 1865). Many astronomers attempted to recover the comet, whose appearance was scheduled for December 1865: among them Donati, with the powerful 28 cm refractor that his predecessor Amici had built for the Florence Observatory. Secchi believed he had found it on 9 December 1865 and communicated the coordinates by telegraph to the astronomer of Florence. Donati followed the object for a few nights and calculated its orbit, which, however, did not correspond to that of Biela’s comet: it was in fact another periodic comet, 4P/Faye (Donati, 1865, 1866a). All further searches were unsuccessful: after 1852, the Comet of Biela was no longer seen.

The 1872 Hoax In mid-January 1872, a catastrophic prediction spread to several newspapers, apparently starting from France. In English, it was published on 18 January by the Parisian Galignani’s Messenger (1872), which says:

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Fig. 4.6 The twin comets of Biela, on their return in 1852, from Secchi’s observations (Guillemin, 1877)

A learned Italian, the astronomer Giovanni Castro, announces the end of the world for January 11, 1877. The shock of a comet is, he declares, to annihilate our unfortunate planet. We are first to be suffocated and then burnt.

On 23 January, the Swiss newspaper Nouvelliste Vaudois of Lausanne reported the “discovery” of the Italian astronomer and relaunched: Here is another serious news that we give to the capitalists and in general to all the people who speculate on the future. […] The astronomy professor Mr. Plantamour in his travels through the celestial vault has just discovered a comet that circulates with such speed that on 12 August it will have met our Earth. Since the aforementioned comet has a considerable volume, there is no possibility of resisting the impact; let us hasten to say that it is not the shock that is to be feared because by the time it occurs, mankind will have long since been suffocated. We have one possibility, Mr. Plantamour said, only one, and that is that this comet encounters a star larger than itself on its path (catastrophe that occurred with Jupiter, which is scientifically proven). Except for this possibility, we must expect to do away with our human squabbles, our miserable interests [...]

Although the source of the first announcement could not be found—nor the alleged “Italian astronomer” identified—the second one was a real joke, as Plantamour himself reconstructed; it was devised by a brigade of idlers gathered in a café in the Saint-Gervais quarter of Geneva, with the intent of having fun of the credulous population (and perhaps, we will say, even of journalists). Among the pranksters was a baker, an acquaintance of Plantamour, who suggested making the news more realistic by adding the name of the Genevan astronomer. Although some newspapers

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reported it as a hoax, it continued to spread locally until it crossed cantonal borders, most likely when it was published at the beginning of February by the Geneva-based English-language newspaper Swiss Times. “At first I laughed about it too” confessed Plantamour to a colleague, “but now it has become too big! Can you imagine that I get piles of letters every day, where they ask me for more information?” (Wiener Kirchenzeitung, 1872: 391). The hoax also landed on some prestigious scientific journals. Nature confuted it with a note explaining that comets can do little damage to our planet: because of their small mass, as demonstrated by Lexell’s comet (D/1770 L1), which passed very close to Jupiter without altering in any way the motion of its satellites, and because of the rarefaction of their tails, such as that of the great comet of 1861 (C/ 1861 J1), which was crossed by the Earth without any damage. The editor concluded ironically by suggesting to people who still feared these celestial objects to make an offer, not to priests, but to the Royal Astronomical Society: “Science would be benefited and, doubtless, the omen would be averted - at all events they always have been” (Notes, 1872:310). Additionally, Scientific American published a piece on the subject; it repeated the same arguments as the English magazine and came on strong at the Genevan astronomer and the press: Of Professor Plantamour we do not find any necessity to speak, never having before heard of that scientist; and our readers’ patience needs not be tried by a lengthy and serious consideration of his theory. But we must express some astonishment at the number of journals who have given space to discussion of the subject; and we respectfully suggest that some public provision be at once made for the education, in the physical sciences, of newspaper editors and writers (A Munchausen comet, 1872).

Despite a rapid denial by Plantamour on the press, the announcement of the end of the world continued to spread, just as it happens with modern fake news. As August approached, fear spread among the superstitious in both cities and the countryside, not only around Switzerland and across the Alps but also as far away as Chile and Australia. Nevertheless, some journalists had fun of it by writing ironic comments and inventing new details (see Bianchi, 2020a for full details and references). “Plantamour’s comet” also became the subject of a futuristic (and ironic) tale by the American journalist William Livingston Alden (1837–1908). The text is devised as a lecture given before the New York Historical Society on 1 April 1932, almost sixty years after the comet’s impact with the Earth. The lecturer narrates the first disbelief at Plantamour’s announcement, the subsequent confirmations, the arrival of the comet and the impact that, seen from the American east coast, resulted in the retreat of the Atlantic Ocean and in a thick fog. A month later, the mists cleared, what had happened became clear: the terrestrial globe had been shattered into several parts, all orbiting, together with the Moon, around what remained of the Americas. One piece corresponded to part of Africa, another to part of Europe: “the Spanish peninsula, and Italy, south of Rome, had disappeared, although the dome of St. Peter’s still shone like a brilliant diamond point of light”. While no traces remained of Russia, China and England, the populations on the fragments still existed and began to communicate with each other thanks to immense writings on the American Great Plains and in Holland, observed with telescopes (Alden, 1872).

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In Italy, the engineer Demetrio Emilio Diamilla-Müller (1826–1908), a controversial figure of scientist and secret agent, published two popular brochures inspired by the debate on the alleged comet (Diamilla-Müller, 1873a, 1873b). In one of these, La fine del mondo, the author reports excerpts from a conversation he had with Plantamour: “Would you believe it, my friend - he [Plantamour] told me - that the extravagance of the public to attribute to me the absurd forecast of the impact of our planet with a comet drags me, in spite of myself, to meditate on the end of the world!” (Diamilla-Müller, 1873a:7). Much of the following text presents Plantamour’s considerations on a possible end of life on Earth, caused by overpopulation, resource exhaustion and global warming.

Debunking the Hoax Early in 1872, the editor of Florentine newspaper La Nazione asked the opinion of Donati on the announced cataclysm. The astronomer had asked Plantamour about the origin of the rumours; however, he had not yet received a reply and could only venture into guessing. As there were no visible (nor telescopic) comets in that period, Donati considered periodic comets: only Biela’s would have adapted to the prophecy, since, according to his own calculations, it would have passed close to Earth’s orbit on 26 August (although not 12). But, as in 1832, the Earth would pass that point on another date, 28 November. However, as Donati wrote to the newspaper, there was a further reassurance: “There is no less the great probability that the Comet of Biela no longer exists!” (Donati, 1872a). For Donati, the comet had largely disintegrated, and the only way to see its remains was through a meteor shower; indeed, the association between meteor showers and periodic comets had been recently demonstrated by his colleague Giovanni Virginio Schiaparelli (1835–1910), director of the Brera Observatory in Milan. Donati (1872a) noted that: [...] every year on 5 December we see shooting stars, which start or radiate from a certain part of the celestial vault, in which the Comet of Biela would appear if in early December found itself in the vicinity of the Earth [...] My supposition that the comet of Biela may have divided into many of those corpuscles that generate shooting stars, would then acquire a greater degree of probability, if in the coming August the astronomers were not able to see that comet, as already they did not succeed in 1866.

Despite these scientific considerations, Donati (1872a) nonetheless had to confess: I have made all this rumour about the Comet of Biela, because I have not found any other fact, or astronomical clue, that can somehow explain the rumour that has generally spread [...] but perhaps this general belief derives from reasons that are anything but astronomical; as the error insinuates itself and spreads much more easily than the truth.

Other Italian astronomers also commented on the subject. Secchi wrote: The news of the next comet is one of the usual canards made to make the public laugh at the expense of poor astronomers. That this comet was predicted by Plantamour is false, and since I am related to him, he never told me anything about it. It is an announcement that is

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repeated periodically, and eventually they will guess a comet that, rightly or wrongly, will be that one (Secchi, 1872).

For Michez, then-director of the Bologna Observatory, “it is a question of simple misunderstanding: of a joke taken seriously, and no longer”. He too associated the news with the comet of Biela, for the period of the forecast and for the name of Plantamour, who had previously calculated its orbit. With considerations similar to those of Donati, Michez dispelled the fears of a comet impact with the Earth and announced. the almost certainty of our periodic meeting towards the end of November with the matter disseminated by it. So no longer fantastic fears of enormous cataclysms, but the peaceful spectacle of one of those showers of pale and fleeting fires that contribute so much to increasing the magnificence of the starry vault (Michez, 1872a).

Additionally, for 1872, Michez calculated the ephemeris, “although there is little hope of being able to observe the comet of Biela” (Michez, 1872b). Curiously, the ephemeris table starts on 12 August, the date of the supposed impact!

The Andromedids For some years already, as Donati and Michez had written, it was suspected that meteor showers observed between the end of November and the beginning of December could be associated with the orbit of Biela’s comet. The Italian Association for the Observation of Luminous Meteors, coordinated by Schiaparelli and the Barnabite Francesco Maria Denza (1834–1894), director of the Meteorological Observatory of the Royal College “Carlo Alberto” in Moncalieri, near Turin, recommended simultaneous observations for that period to accurately identify the point of the celestial vault, the radiant, from which they appeared to originate (Denza, 1870). Analysing the copious observations of meteors by the Bergamo amateur astronomer Giuseppe Zezioli (circa 1830–1870), Schiaparelli made known that the radiant of a meteor shower observed on 30 November 1867 was compatible with the latest calculated orbits of 3D/Biela and that the date of appearance seemed to be earlier than the swarms previously seen in December, just as the comet’s orbit, due to gravitational perturbations, anticipated the moment in which it intersected the terrestrial one (Schiaparelli, 1870). Since the comet of Biela—or what remained of it—would soon pass by that point, the alert was high for a large shower of shooting stars at the end of November 1872: it had already been observed that a meteor shower was reinvigorated from the recent passage of the associated comet, as happened, for example, for the great rain of the Leonids of 1866, which occurred after the arrival of the 55P/ Tempel-Tuttle (Herschel, 1872). Even that year, the searches for the comet of Biela were vain. Obviously, the comet did not show itself in correspondence with the catastrophic forecast to which it was associated, but not even when it was close to perihelion, at the beginning of October (Secchi, 1873). The expectations of a copious shower of shooting stars, however,

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Fig. 4.7 The meteor shower of 27 November 1872 (Guillemin, 1877)

were met, and a splendid show occurred on the night of 27 November: at the peak of the phenomenon, early in the night in Europe, up to 200 meteors could be counted per minute (Fig. 4.7). The radiant was near the star γ Andromedae (hence the name Andromedids, but the shower is also called Bielids), very high in the sky, so that the phenomenon looked like a rain of stars. Schiaparelli and Denza (1872) gave an account of the numerous Italian and foreign observations made on that night. The meteor shower was not observed in Florence because of bad weather. However, the editor of the local newspaper La Nazione again asked Donati to intervene, since the predictions in his March article had shown “the proof of their scientific rigor”. In his reply, Donati first returned to the announcement of the end of the world, reporting passages from a letter received from Plantamour explaining the origin of the hoax; then, he triumphantly presented his conclusions: I therefore do not believe that the rain of the stars, observed from 27 to 28 of last month, is due to the encounter of the Earth with the tail of the Comet of Biela but to the encounter of Earth with the remains of the former Comet, whose death gloriously revealed itself to the human gaze with torrents of fire! (Donati, 1872b)

However, not all astronomers agreed with the idea that the comet had totally disintegrated. Despite the published ephemerides, the German astronomer Wilhelm Klinkerfues (1827–1884) believed that the meteors were associated with the passage of the comet itself in the vicinity of the Earth. For this, he promptly telegraphed his English colleague Norman R. Pogson (1829–1891) at the Observatory of Madras, India, inviting him to look for the comet in the vicinity of the star θ Centauri (in the

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direction opposite to the radiant of the meteors). On the morning of 3 December, Pogson identified an object with a cometary appearance, which he also found the following day but which was then no longer observed due to bad weather conditions. Pogson’s comet (X/1872 X1) was therefore initially identified as one of the two fragments of the Biela comet. Schiaparelli, who also believed in comet survival, saluted Pogson’s discovery (Schiaparelli, 1873). A controversy arose between Donati and Schiaparelli on this topic, but it rapidly waned as it became clear that the position of Pogson’s object was incompatible with the known path of Biela’s comet (see Bianchi, 2020a for details). Donati verified it on his own: sheets with the calculated position of Biela’s comet on 2 December 1872, in his handwriting, are still conserved in the Historical Archive of the Arcetri Observatory (Fondo Donati).

Wilhelm Tempel In 1872, the main building of the new Florentine Observatory was inaugurated on the hill of Arcetri, thanks to the hard work of Donati. Unfortunately, the astronomer died the following year (Bianchi, 2020b). While waiting for the authorities to complete the equipment at Arcetri and eventually appoint a new director, Schiaparelli recommended the German Wilhelm Tempel (1821–1889) for the post of assistant astronomer. Originally a lithographer, Tempel had begun his astronomical adventure as an amateur astronomer in Venice, had worked briefly at the Marseille Observatory, and since 1871 was assistant at the Brera Observatory. He was a skilled observer and draftsman and had already discovered 11 comets and 5 asteroids. Schiaparelli promoted his employment in Florence with these words: I think [that Tempel] could be suitable for the Florence Observatory, especially in this transition period that is about to begin, […] The Observatory of Florence could also in this interval give an account of the reasons for its existence by contributing to the progress of astronomy with the kind of discoveries that make most impression on the public, that is, with the discovery of new celestial bodies (Bianchi et al., 2011:57–58).

Tempel arrived in Arcetri in January 1875. He was soon captured by the possibility offered by the 28-cm Amici refractor of the Observatory to observe nebulae and devoted most of his time to searching and drawing them. Because of this, Tempel dedicated less time to the activity that had made him known, thus somehow neglecting the role of “discoverer of celestial bodies” he was asked to fulfil. Still Tempel discovered in Arcetri one last comet, C/1877 T1, using the Amici telescope. This discovery was also at the center of another “fake news” or, perhaps, a joke: in a letter to a Sicilian newspaper, the local amateur astronomer Giulio Tomasi di Lampedusa (1813–1885) declared that he had observed the comet first; however, Tomasi di Lampedusa had not written that letter, and he rapidly sent a denial to the press and to Tempel. Later, Tempel said that this attempt at “stealing” his discovery put him off searching for new comets (Bianchi & Chinnici, 2014; Chinnici, 2015). Nevertheless, Tempel continued to observe comets from Arcetri: he measured the

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positions of many objects, recovered a few periodical comets including “his own” 9P/Tempel and 10P/Tempel, and made exquisite drawings of some bright comets visible to the naked eye, such as C/1881 K1 (Fig. 4.8).

Fig. 4.8 The head of comet C/1881 K1 from unpublished drawings by Tempel dated 24, 25, 27, 28, 29, and 30 June 1881 (from I to VI, respectively; Historical Archive of the Arcetri Observatory, Fondo Tempel)

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Florence as the “Headquarter of Comets”? A Final Balance With Tempel, the romantic period of comet observations from Florence ends. Comets were still observed in Arcetri after him, but no new discovery was made, and all efforts were dedicated to measuring celestial positions of known objects. Including only comets for which the discoverer was the first observer, more than one-third of all comets discovered from Italy in the nineteenth century were found from Florence by Pons, Donati and Tempel: 13 out of the total national tally of 35 (Table 4.1). The second place in the ranking is taken by Rome, with six comets discovered by De Vico and one by Secchi; third come the four comets discovered by Pons from the Specola of Marlia in the Duchy of Lucca. Three comets were discovered in Bologna by Lorenzo Respighi (1824–1889) and in Milan by Tempel. A comet each was discovered in Parma by Antonio Colla (1806–1857), in Naples by Christian Heinrich Friedrich Peters (1813–1890), and in Palermo by Temistocle Zona (1840–1910). Table 4.1 Comets discovered in Italy in the nineteenth century Florence

Collegio Marlia (Lucca) Bologna Brera Other Romano (Rome) (Milan) observatories

Other locations

C/1825 P1 Pons

54P/1844 Q1 de Vico

C/1821 B1 Pons

C/1862 C/1871 W1 L1 Respighi Tempel

80P/1846 M1 C. H. F. Peters Capodimonte (Naples)

C/1807 R1 Parisi Castrogiovanni (currently Enna)

C/1825 V1 Pons

C/1845 D1 de Vico

C/1822 K1 Pons

C/1863 C/1871 G2 V1 Respighi Tempel

C/1847 J1 A. Colla Parma

C/1859 G1 Tempel Venice

C/1826 P1 Pons

C/1846 B1 de Vico

C/1822 N1 Pons

C/1863 10P/ Y1 1873 Respighi N1 Tempel

C/1890 V1 T. Zona Palermo

C/1826 U1 Pons

122P/1846 D1 de Vico

C/1825 N1 Pons

C/1826 Y1 Pons

C/1846 01 de Vico

D/1827 M1 Pons

C/1846 S1 de Vico

C/1827 P1 Pons

C/1853 E1 Secchi

C/1855 L1 Donati C/1857 V1 Donati (continued)

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Table 4.1 (continued) Florence

Collegio Marlia (Lucca) Bologna Brera Other Romano (Rome) (Milan) observatories

Other locations

C/1858 L1 Donati C/1864 O1 Donati & Toussaint C/1864 R1 Donati C/1877 T1 Tempel Arcetri Notes: for the sake of simplicity, we indicate (in italics) only the names of the discoverers from Italy and omit eventual codiscoverers abroad. Names in bold indicate the place of discovery (all established observatories, except for those in the last column). See Kronk (2003) for further details

To these discoveries made by astronomers employed in professional observatories, we must add two other comets: the great comet of 1807, C/1807 R1, first seen by the monk Parisi, an occasional observer (Chinnici, 2015); and C/1859 G1, discovered in Venice by a novice amateur astronomer with his telescope, the Tempel we already know (Bianchi et al., 2010). Comet C/1807 R1 was first observed from the Sicilian city of Enna, which at the time was still named Castrogiovanni. One might wonder if the inventor of the first comet hoax of 1872 took inspiration for the alleged astronomer “Giovanni Castro” from a report of the discovery of the 1807 object in a historical résumé of comet observations. Even the excellent Kronk (2003) confuses the name of the place with that of the discoverer, by saying that C/1807 R1 was found by C. Giovanni (Chinnici, 2015). To close our balance, we can conclude that Florence had indeed become the headquarters of comets, as von Zach hoped for in 1825, but only on an Italian level. In the nineteenth century, in fact, Marseille was the city with the most discoveries, as many as 45, testifying to the value of the astronomers who contributed to it (including Pons and Tempel themselves) and the clear skies of the French city. However, at the end of the century, Marseille was giving way to observations from the other side of the Atlantic and to the ever-increasing contribution of amateur astronomers.

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References Alden, W. L. (1872). After the comet. The Aldine, 5(7), 136–137. A Munchausen comet, Scientific American, 3/16/1872, 26(12), p. 183. Annuario dell’I. e R. Museo di Fisica e Storia Naturale per il 1859 (1858). Firenze, Le Monnier. Arago, F. (1855). Astronomie populaire, Vol. 2. Paris, Gide & Baudry. Bianchi, S. (2020a). Le comete a Firenze e la fine del mondo nel 1872. Giornale di Astronomia, 46(3), 37–45. Bianchi, S. (2020b). The founding of Arcetri observatory in Florence. Journal of Astronomical History and Heritage, 23(3), 553–581. Bianchi, S., & Chinnici, I. (2014). L’arrubbatina della cometa. Giornale di Astronomia, 40(2), 38–41. Bianchi, S., Galli, D., & Gasperini, A. (2011). Giovanni Virginio Schiaparelli e l’Osservatorio di Arcetri. Firenze, Fondazione Giorgio Ronchi. Bianchi, S., Galli, D., & Gasperini, A. (2016). The origins of Astrophysics in Florence. In I. Chinnici (Ed.), Starlight, the origins of Astrophysics in Italy (pp. 14–33). Arte’m. Bianchi, S., Gasperini, A., Galli, D., Palla, F., Brenni, P., & Giatti, A. (2010). Wilhelm Tempel and his 10.8-cm Steinheil Telescope. Journal of Astronomical History and Heritage, 13(1), 43–58. Branham, R. L., Jr. (2014). A new orbit for comet C/1858 L1 (Donati). Astronomische Nachrichten, 335, 135. Celoria, G. (1921). Sulle osservazioni di comete fatte da Paolo dal Pozzo Toscanelli e sui lavori astronomici suoi in generale. Milano, Hoepli. Cesana, G. A. (1890). Ricordi di un giornalista, Milano, Tipografia Bortolotti. Chinnici, I. (2015). Nineteenth-Century comets: Studies and observations in Sicily. Journal for the History of Astronomy, 46(2), 130–158. Covoni Girolami, M. (1981). Ricordi e memorie di un personaggio fiorentino, Firenze, Cassa di Risparmio di Firenze. Denza, F. (1870). Norme per le osservazioni delle meteore luminose. Collegio degli Artigianelli. Diamilla-Müller, E. (1873a). Letture scientifiche per il popolo italiano: Lettura I: La fine del mondo. Milano, Dumolard. Diamilla-Müller, E. (1873b). Letture scientifiche per il popolo italiano: Lettura V: L’urto di una cometa contro la terra. Milano, Dumolard. Donati, G. B. (1864). Schreiben […] an den Herausgeber. Astronomische Nachrichten, 62, 375–376. Donati, G. B. (1865). Varietà-Astronomia. Gazzetta Ufficiale del Regno d’Italia, December 22. Donati, G. B. (1866a). Brevi cenni intorno alla cometa periodica di Biela, e osservazioni della cometa periodica di Faye. Nuovo Cimento, 22, 78–80. Donati, G. B. (1866b). Sulle apparenze fisiche della cometa V del 1858. Annali del R. Museo di Storia Naturale di Firenze per il 1865, nuova serie, vol. I, p. 56. Donati, G. B. (1872a). Dell’urto di una cometa con la Terra. La Nazione, March 4. Donati, G. B. (1872b). Ancora sull’urto di una cometa con la Terra. La Nazione, December 10. Donati, G. B. (1873). Letter to Schiaparelli, January 12 (Archivio INAF-Brera, Corrispondenza Scientifica) Encke, J. F. (1820). Ephémérides de la Comète d’Encke pour l’année 1822. Correspondance Astronomique, Géographique, Hydrographique Et Statistique, 4, 262–269. Galignani’s Messenger. (1872). January 18. Galli, D., Gasperini, A., & Bianchi, S. (2013). Dalla meccanica celeste alla spettroscopia stellare. Corrispondenza tra Giovanni Battista Donati e Ottaviano Fabrizio Mossotti. Atti della Fondazione Giorgio Ronchi, 68(1), 15–84. Galli, D., Gasperini, A., & Bianchi, S. (2016). Il primo spettro di una cometa. Giornale di Astronomia, 42(1), 43–45. Gasperini, A., Galli, D., & Bianchi, S. (2011a). La cometa del Risorgimento. Giornale di Astronomia, 37(3), 9–14.

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Gasperini, A., Galli, D., & Nenzi, L. (2011). The worldwide impact of Donati’s comet on art and society in the mid–19th century. Proc. IAU Sym. No. 260, pp. 340–345. Cambridge: Cambridge University Press. Guillemin, A. (1875). Les comètes. Hachette. Guillemin, A. (1877). Le Ciel: Notions élémentaires d’astronomie physique. Hachette. Herschel, A. S. (1872). Observations of Meteor Showers, supposed to be connected with Biela’s Comet. Monthly Notices of the Royal Astronomical Society, 32, 355–359. Hill, G. W. (1866). New elements and ephemeris of the great comet of 1858. Astronomische Nachrichten, 64, 181–190. Kronk, G. (2003). Cometography, a catalog of comets, Vol. II, 1800–1899. Cambridge, Cambridge University Press. Michez, J. (1872a). La cometa di Biela. Monitore di Bologna, May 18. Michez, J. (1872b). Schreiben […] an den Herausgeber. Astronomische Nachrichten, 79, 331–332. Notes, “Nature”, 2/15/1872, 5 (120), p. 310. Nouvelliste Vaudois. (1872). January 23. Olbers, H. W. (1828). Über den Biela’schen Cometen bei seiner nächsten Wiederkunft im Jahr 1832. Astronomische Nachrichten, 6, 155–160. Pasachoff, J. M., Olson, R. J. M., & Hazen, M. L. (1996). The earliest comet photographs: Usherwood, Bond, and Donati 1858. Journal for the History of Astronomy, 27, 129. Santini, G. (1865). Elementi ed Effemeride per il ritorno al perielio della Cometa di Biela atteso per il 1866 dietro i calcoli del Sig. Dr. Giacomo Michez. Astronomische Nachrichten, 63, 297–300. Secchi, A. (1872). Letter to A. Ronchi, March 15. In Gazzetta Ufficiale del Regno d’Italia, March 21. Secchi, A. (1873). Le stelle cadenti del 27 novembre 1872. Atti dell’accademia Pontificia Dei Nuovi Lincei, 26, 1–13. Schiaparelli, G. V. (1870). Alcuni risultati preliminari tratti dalle osservazioni delle stelle cadenti […]. Effemeridi astronomiche di Milano per l’anno 1871, 405–428. Schiaparelli, G. V. (1873). La Lombardia, January 7. Schiaparelli, G. V., & Denza, F. (1872). Sulla grande pioggia di stelle cadenti prodotta dalla cometa periodica di Biela e osservata la sera del 27 novembre 1872. Rendiconti del R. Istituto Lombardo di scienze e lettere, s. 2(5), 1173–1235. Wiener Kirchenzeitung für Glauben, Wissen, Freiheit und Gesetz (1872). 25(25), June 22. Zach, F. X. (1825). Les quatre comètes de l’an 1825. Correspondance Astronomique, Géographique, Hydrographique Et Statistique, 13, 182–195.

Chapter 5

The Discovery of Ceres: A “Scientific Comedy” Ileana Chinnici

Abstract The first asteroid—now classed as a dwarf planet—was discovered by Giuseppe Piazzi in Palermo in 1801. From the beginning, its discovery created misunderstandings, misinterpretations, doubts and suspicions. Here, the entire story has been reworded and represented as a “comedy” with a succession of dramatic events, coups de théatre and a happy ending, in the full respect of its historicity. This is a fun example of how scientists, like all people, are no more than actors of the great “human comedy”.

Introduction The discovery of Ceres has been quite extensively studied in recent historiography1 and this chapter does not pretend to add new elements to a well-known story. It rather intends to “read” the whole story in a different light, that of a “scientific comedy”. In fact, the succession of events could have been a perfect plot outline for a Goldonian comedy or an “opera buffa” by coeval musician Giovanni Paisiello (1740– 1816). Consequently, the narration here is presented as a fun theatrical “canovaccio”, describing the various comedy elements of the story as an expression of the culture of that time.

1

See, for instance, Cunningham (2016); other publications are reported in bibliography: Chinnici and Foderà 2001; Foderà and Chinnici 2001; Chinnici 2015b. I. Chinnici (B) INAF Osservatorio Astronomico di Palermo, Palermo, Italy e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_5

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Fig. 5.1 The Palermo astronomical observatory in 1802 (Bode, 1802)

Setting The story takes place at the Palermo Astronomical Observatory at the very beginning of the nineteenth century. The Observatory had been established a decade earlier, in 1790, by Ferdinand of Bourbon, King of the Two Sicilies (Accademia de’ Regj Studj).2 It was part of a general reform of scientific education, which also included the creation of a Botanical Garden and an Anatomical Amphitheater, after the institution of the Royal Academy for Education in 1778. The Observatory (Fig. 5.1) was built on the top of a tower of the Royal Palace as a strict alliance between science and power, following both the Enlightenment and Freemason principles.3 At the time of the discovery of Ceres, Sicily was, on the political and commercial planes, a sort of English protectorate because of some kind of anti-Napoleonic alliance.4 The King had escaped from the capital, Naples, in 1799, in front of the advancement of the Napoleonic army in Italy and took refuge in Palermo, where the English fleet barred every French attempt to conquer the island. Nevertheless, contacts with France were kept in the cultural contexts, more or less explicitly, especially through the Freemason Lodges. 2

See Foderà 1993. See Coniglio et al. 2020. 4 See D’Andrea 2006. 3

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Protagonist Giuseppe Piazzi (1746–1826) (Fig. 5.2) was the Director of the Palermo Observatory. He was born in Northern Italy, entered the religious order of the Theatines and taught mathematics in various places.5 He was a fairly obscure mathematician when he was called to hold the chair of astronomy in Palermo in 1786. The salary was low, the cultural context was considered unattractive and renowned astronomers had already declined the invitation to work in Palermo. Faute de mieux, Piazzi was appointed professor of astronomy by the Royal Academy for Education and charged with building an astronomical observatory. Theoretical astronomy was part of the background in mathematics, but he lacked experience with telescopes and observing methods and therefore asked the King permission to go abroad to practice astronomy and purchase some first-quality instruments. He spent a couple of years between Paris and London and came back to Palermo with excellent equipment for the new Observatory. The most important instrument was the Ramsden Circle (Fig. 5.3), a unique telescope made in London by the famous instrument maker Jesse Ramsden Fig. 5.2 Portrait of Giuseppe Piazzi (Museo della Specola, INAF–Osservatorio Astronomico di Palermo and Sistema Museale di Ateneo, Università di Palermo)

5

For a detailed biography of Piazzi, see Maineri 1871 and Invernizzi et al. 2001.

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Fig. 5.3 The Ramsden Circle (Piazzi, 1792)

(1735–1800). It was designed as a precision instrument for astrometric studies;6 once it was installed at the Observatory, Piazzi used it for making a star catalogue, which he published in 1803 and, as a second—revised and extended—edition, in 1814. During the observations for the redaction of the catalogue, Piazzi and his assistants discovered Ceres on the night of January 1st, 1801.

The Missing Coprotagonist Niccolò Cacciatore (1770–1841), Piazzi’s assistant, could be considered to be a coprotagonist. Actually, he played only a minor role in the discovery of Ceres. Although he later pretended to be the real discoverer, his statement should be confirmed by other circumstances that require further investigation. For instance, it is well known that Piazzi, who was sincerely affectionate to Cacciatore, recognized his role in the redaction of his star catalogue but never mentions him in relation to Ceres, except for some attempts to observe it out of the meridian in the nights following 6

See Chinnici 2009 and Chinnici et al. 2001.

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the actual discovery. Consequently, Cacciatore is here considered just a supporting actor.

Other Actors Barnaba Oriani (1752–1832) (Fig. 5.4): Astronomer at the Brera Observatory in Milan, Piazzi’s friend and confident, is the first person to whom he communicates the discovery. Oriani plays a crucial mediation role between Piazzi and the international astronomical community because he circulates the news of the observation of a new celestial object and defends Piazzi’s paternity of the discovery. Johann Elert Bode (1747–1826) Director of the Berlin Observatory, one of the most reputed astronomers of his time, was convinced of the existence of a planet between Mars and Jupiter. Piazzi writes to him stating that he discovered a comet without a visible coma or tail, therefore indirectly suggesting that it was a planet. Bode animates the international debate on the discovery and suggests names for the new celestial body. Franz Xaver von Zach (1754–1832) German astronomer, active communicator, established the Mönatlische Correspondenz, a sort of monthly astronomical bulletin. He is one of Bode’s main correspondents and expresses vitriolic comments on Piazzi’s reticence to share the data of his observations of the discovered object. Jérôme de Lalande (1732–1807) One of the main French astronomers of his time, is considered a mentor by Piazzi, who had frequented Lalande’s lessons in astronomy during his stay in Paris. They are also connected by Freemasonry, as both belonged to this organization and Lalande was the master mason of a French lodge. Piazzi frequently asked Lalande’s advice on works, instruments, and other astronomical matters and referred to him as an authority in the field. In Ceres’ case, however, Piazzi had an ambiguous attitude toward his mentor and did not clearly speak with him about his discovery.

Guest Stars Nevil Maskelyne (1732–1811) Astronomer Royal at the Greenwich Observatory welcomed Piazzi at the Observatory during his stay in London; together, they observed a solar eclipse in 1788, and Maskelyne presented to the Royal Society a letter on this subject by Piazzi, which was later published in the Philosophical Transactions. The Astronomer Royal shows an attitude of criticism and suspicion against Piazzi on the occasion of the discovery of Ceres.

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Fig. 5.4 Portrait of Barnaba Oriani (Museo della Specola, INAF–Osservatorio Astronomico di Palermo and Sistema Museale di Ateneo, Università di Palermo)

Carl Friedrich Gauss (1777–1855) Young and brilliant mathematician who understands the importance of finding a mathematical solution to the difficult question of the calculation of Ceres’ orbit and successfully solves the problem. This permitted astronomers to retrieve Ceres, which had become unobservable during its motion around the sun. Frederick William Herschel (1738–1822) One of the most reputed astronomers and telescope makers of his time, discoverer of Uranus and pioneer in the study of nebulae and the Milky Way. He identifies Ceres as belonging to a new class of celestial objects, which he calls “asteroids”.

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Cameo Appearances Pierre Simon de Laplace (1749–1827) “Prince” of the French mathematicians and father of celestial mechanics, scientist and politician, enters the debate only to suggest a name for the new “planet”. Napoleon Bonaparte (1769–1821) In the midst of his political rise, he, like de Laplace, proposes a name for the newly discovered object.

Extras Johann Daniel Tietz (in Latin, Titius) (1729–1796) Danish naturalist who first identified the geometric progression describing the distance of the planets from the Sun. Johann Karl Burckhardt (1773–1825) Mathematician, expert in celestial mechanics, first worked as an assistant at the Gotha Observatory and then moved to Paris, where he was Lalande’s collaborator and worked at the Bureau des Longitudes. Johann Hieronymus Schroeter (1745–1816) Lawyer and astronomer, hosted in his own private observatory the first meeting of the Society of Lilienthal (see below) and assiduously looked for the “lost” planet (see below). Heinrich Wilhelm Matthias Olbers (1758–1840) Physician and astronomer, was among the most active members of the Society of Lilienthal (see below) and discoverer of both the second and fourth asteroids, Pallas and Vesta. Pierre Méchain (1744–1804) and Jean-Baptiste Delambre (1749–1822) The first French astronomers who observed Ceres, in 1802, after their German colleagues. Karl Ludwig Harding (1765–1834) German astronomer who discovered the third asteroid, Juno.

The Backstory In 1766, naturalist Titius constated that the distances of the planets from the sun follow an empirical law, described by a geometrical progression, with a gap between Mars and Jupiter. The publication of this law by Bode in 1772 in his work Anleitung zur Kenntniss des gestirnten Himmels attracted the attention of astronomers, who started to suspect the existence of an unobserved planet that filled the gap. When the discovery of Uranus in 1781 confirmed the validity of the law, with the new planet

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exactly at the expected distance, a group of German astronomers, fully convinced that no gap should exist, decided to chase down the missing planet between Mars and Jupiter. In 1800 they met at Lilienthal, near Bremen, and established an association for revising the existing ecliptic charts to seize the planet, possibly inviting astronomers from other countries to join them. Bode and von Zach were among the most active members and leaders of this association, and they started the planet hunt.

The Discovery In the meantime, while working on his star catalogue, Piazzi stumbles upon the unexpected discovery. He later writes: While so much zeal animated Europe, Germany in particular, being myself separated from the mainland, only supported by scarce and rare correspondence by letters, due to the calamitous circumstances of the time; by all means unaware of the established society, and of the honor of having been included on the list of twenty-four cooperating Astronomers; guided only by the observing method which I embraced, unwittingly, unthinkingly, I opportunely spotted the coveted Planet.7

It is important to pay attention to Piazzi’s words. He was isolated (separated from the mainland) not only because of his geographic position but also because of the Napoleonic wars (the calamitous circumstances of the time), which hampered regular mailing correspondence (scarce and rare correspondence by letters) and consequently made him unaware of the establishment of the new association (unaware of the established society). He seized the planet thanks to his observing method (guided only by the observing method that I embraced)—a statement that deserves a few explaining words. Piazzi was used to reobserve the same star for several nights to improve the measurements by reducing the reading error. In fact, his initial hope to attain an accuracy of less than one arcsecond soon vanished when he constated that the Ramsden Circle was significantly affected by the thermal expansion, so that the upper and the lower parts of the instrument had different temperatures in the hot Sicilian nights. Consequently, he could improve the accuracy by simply repeating the measurements. Once Piazzi repeated the measurements of the position of the new star, he could recognize from its motion that the celestial object he had observed was not a star.

7

... Mentre tanto zelo animava l’Europa, e la Germania in particolare, disgiunto io dal continente, non avvalorato, che da poche, e rare corrispondenze letterarie per le calamitose circostanze dei tempi; ignaro affatto della stabilita società, […] guidato solo dal metodo da me abbracciato di osservare, senza volerlo, senza pensarlo colsi felicemente il tanto desiderato Pianeta. (Piazzi, 1802, pp. 13–14).

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The Announcement of the Discovery (And the False Trail) On January 24, 1801, when he is quite sure of his discovery, Piazzi writes to his friend Oriani: On the 1st of January I observed in Taurus an 8th magnitude star […] from 10 to 11 [January], from a position of retrograde motion it became direct, […] I have announced this star as a comet, but owing to its lack of nebulosity, and to its motion being so slow and rather uniform, I had the suspicion that it could be something better than a comet. However, I should be very careful in passing this conjecture to the public. Once I have collected a greater number of observations, I will then attempt to calculate its [orbital] elements.8

At the same time, Piazzi sends a similar letter to Bode, in which he announces the discovery of a comet “without nebulosity”,9 indirectly suggesting that the comet is actually a planet. Again, let us pay attention to Piazzi’s words. He deliberately announces to have discovered a comet (I have announced this star as a comet), although he is sure that this is not the case because of its appearance and motion (owing to its lack of nebulosity and to its motion being so slow and rather uniform); he does not dare to use the word “planet” (something better than a comet), but he is clearly suggesting to Oriani that it is a planet, even if he intends to keep secret “this conjecture” until the calculation of the orbital elements confirms his suspicion. The red herring of announcing the discovery of a comet instead of a planet is the first serious mistake made by Piazzi. He wants to gain time to calculate the orbital elements of the new planet, but he does not succeed. Moreover, he is under pressure for the completion of the meridian line in the renewed Cathedral of Palermo, to be inaugurated in June. He enters into a spiral of tensions that stresses him to the point that he falls ill and leads him to make further errors. Imprudently, Piazzi does not consider the consequences of his false announcement: actually, the astronomical community wants to observe the discovered “comet”. The first reaction comes from his mentor, Lalande (Fig. 5.5), who asks him for the data of his observations: … having read in the Journal de Paris, about a comet discovered in Palermo, I wrote to M. Piazzi on 27th February [1801], to ask for the data of his observations …10

Piazzi would take his time but cannot ignore the request from Lalande; he is therefore forced to provide the data of the observations, still speaking of a comet. 8

Il dì 1° di gennajo osservai nella spalla del Toro una stella di 8a grandezza, [...] Dai 10 agli 11 di retrograda divenne diretta ... […] Io ho annunziato questa stella come cometa, ma il non essere essa accompagnata da alcuna nebulosità, e più il suo movimento così lento e piuttosto uniforme, mi ha fatto cadere nell’animo che forse possa essere qualcosa di meglio di una cometa. Questa congettura però mi guarderei bene di avanzarla al pubblico. Quando avrò un maggior numero di osservazioni, tenterò di calcolarne gli elementi. (Piazzi to Oriani, 24 Jan 1801, in Corrispondenza Astronomica …, pp. 48–49). 9 See Bode 1802, p. 2. 10 ... ayant lu dans le Journal de Paris, qu’on avait découvert une comète à Palerme, j’écrivis à Piazzi, pour lui demander ses observations. (Lalande 1803, p. 455).

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Fig. 5.5 Portrait of Jérôme de Lalande (Museo della Specola, INAF–Osservatorio Astronomico di Palermo and Sistema Museale di Ateneo, Università di Palermo)

I had decided not to communicate my observations to anyone before having drawn from them the elements of the comet; but you are the one asking me, I have no more objections: you will find it attached.11

Piazzi is impatient to receive a reply from Oriani, the only one who knows the true discovery; he does not know that his friend has not yet received his letter and writes again to him, asking for his help for the calculation of the orbital parameters of the “comet”: … I sent you some data on the observation of a comet that I discovered on the 1st of January and that I observed continuously until the 11th of February. After that time, I fell critically ill, and I am not yet fully recovered. Since in the past days I received a letter from M. La 11

Je m’étais proposé de ne communiquer mes observations à personne, avant d’en avoir tiré les éléments de la comète; mais c’est vous qui me le demandez, je n’ai plus d’objections: vous le trouverez ci-jointes. (Ibid., p. 455).

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Fig. 5.6 Portrait of Johann E. Bode (Hamburg State and University Library Carl von Ossietzky, via Wikimedia Commons)

Lande, where he urged me to send him the data of the observations, I have sent him those of the comet, as now I am not in a condition to work. The same data I send also to you, but I beg you not to publish them. If you like to make calculations from them, I hope you will communicate to me the results.12

Again, he sends another letter to Bode (Fig. 5.6) with similar content but without the data of the observations. The first letters by Piazzi to Bode and Oriani are received by the end of March and the beginning of April 1801, respectively. Bode immediately recognizes that “the comet” could be the missing planet that they were looking for and writes to von Zach: Through a simple calculation … I found that both the observations of January 1 and 23 as well as the stationary position of January 11, agreed perfectly with the hypothesis that this

12

... vi mandai alcune osservazioni di una cometa da me scoperta il dì 1 gennaio, la quale continuai interrottamente a vedere sino agli 11 di febbrajo. Dopo tal tempo caddi gravemente ammalato, nè sono ancora interamente ristabilito. Come ne’ scorsi giorni ebbi lettera da M. La Lande, che mi sollecita di mandargli delle osservazioni, gli ho inviate quelle della cometa, non essendo io per ora in grado di qualsiasi applicazione. Le medesime mando pure a voi, ma vi prego di non pubblicarle. Se vi prenderà talento di calcolarle, spero che me ne comunicherete i risultati. (Piazzi to Oriani, 11 April 1801, Corrispondenza astronomica …, p. 49).

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He decides to name the new planet Juno, somehow considering himself as having this right, which is usually reserved for the discoverer. Zach, however, had already named the unseen planet Hera–a name that received approval from Laplace and even from Napoleon; later, Lalande goes to the aid of his Italian disciple and, fearing that he could be deprived of this right, assigns to the new object the name of “Piazzi”, according to the French custom to name the celestial bodies with the name of their discoverer (Uranus, for instance, was called “Herschel” in the French astronomical community for many years).

Precautions from a Friend Once he received the letter, Oriani immediately recognizes that Piazzi has discovered the unknown planet. At the same time, he well understands the risks of the misleading announcement given by Piazzi and prudently decides to remedy them by writing to von Zach to circulate the news; he informs Piazzi about his initiative: I rejoice with you for the beautiful discovery of this new star. I don’t believe that others had observed it […] due to its faintness. I assume that you have continued your observations until its immersion in sunlight, and now you are in a condition to establish if it is truly a new planet. I look forward to receiving from you a letter with more precise news in this regard. In the meantime, I have sent an extract of your previous letter to the astronomer in Gotha [von Zach] to be published in its journal …14

In his words, Oriani seems to suggest and kindly encourage Piazzi to speak openly about the new planet: he evidently knows the insecure character of his friend and probably foresees that his hesitant attitude would get him in trouble. Moreover, Oriani is aware of the urgence to circulate the news and conveniently thinks that the publication of the letter in Baron’s Correspondenz would rightfully credit Piazzi as the discoverer of the planet and thus secure his paternity. In his letter to von Zach, Oriani writes: I am right now in possession of a letter by Piazzi from Palermo, which contains a notice that must be taken into serious account by you and all astronomers. He reports having observed a star of magnitude between 8 and 9 on January 1, 1801 in the shoulder of Taurus. [...] He also writes of having initially announced this star as a comet, and only after regularly 13

Bode to von Zach, 14 Apr 1801, in Bode 1802, pp. 3–4 (original text in German). Mi rallegro con voi della bella scoperta di questa nuova stella. Io non credo che altri l’abbiano osservata […] atteso la sua piccolezza. Mi immagino che avrete continuato le vostre osservazioni fino alla sua immersione nei raggi solari, e che sarete a quest’ora in grado di decidere se essa è veramente un pianeta nuovo. Aspetto con impazienza una vostra lettera che mi dia delle nuove più precise in questo proposito. Intanto mandai l’estratto della vostra precedente lettera all’astronomo di Gotha [von Zach] perchè venga pubblicato nel suo giornale… (Oriani to Piazzi, 15 April 1801, in Corrispondenza astronomica …, pp. 49–50).

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observing that it had no nebulosity and very slow motion, had he repeatedly come to the suspicion that it could actually be a planet. Unfortunately, this letter, written on January 24, has been travelling for 71 days; it was therefore difficult to estimate the position of this new moving object, only by those two measurements given by Piazzi. Meanwhile, I tried to take advantage of the fact that on January 10, this object, from being retrograde, resumed its forward motion, and in the hypothesis of it having a circular orbit, I found its distance from the sun to be equal to three semidiameters of the Earth’s orbit; hence, this object could well be a new planet whose orbit would lay between those of Jupiter and Mars. The orbit of this planet, just like that of all others, is likely to be significantly eccentric [...] and therefore my hypothesized circular orbit is likely to be inadequate to determine correctly its motion and its geocentric position after all this time. We must therefore wait for further observations that Piazzi has surely done. [...] In the meantime, I hope you receive this letter early, hopefully before the star gets lost in the sunlight; perhaps, thanks to your finer instruments, you will be fortunate enough to locate it and inform me with more accurate news.15

Baron von Zach (Fig. 5.7) replied: … dear friend, I have been looking for the planet based on the orbital elements you sent me, but unfortunately it is too late and the Object is already immersed into sunlight and in the horizon’s haze. In vain I attempted on several fine nights, and Bode tells me that he was not fortunate either [...] Please send me new orbital elements as soon as you get more accurate ones for it will be difficult to find such a small body at dusk, if its location is not certain and it will be necessary to wait too long to observe it again at the meridian, while I would like to catch to it up as soon as possible.16 15

Ricevo proprio ora una lettera da Palermo di Piazzi contenente una comunicazione che merita la massima attenzione da parte sua e di tutti gli astronomi. Egli scrive di avere osservato il primo gennaio 1801 nella spalla del Toro una stella di grandezza tra 8 e 9. […] Scrive inoltre di avere annunciato inizialmente questa stella come cometa e solo dopo averla osservata costantemente senza nebulosità e con un moto molto lento, era più volte giunto all’idea e al sospetto che potesse essere effettivamente un pianeta.

Sfortunatamente questa lettera, scritta il 24 gennaio, è stata in viaggio per 71 giorni; era perciò difficile stimare la posizione di questo nuovo Astro in movimento unicamente dalle due posizioni date da Piazzi. Nel frattempo ho tentato di sfruttare il fatto che il 10 gennaio questo Astro è passato da moto retrograde a moto diretto e, nell’ipotesi di un’orbita circolare, ho trovato che la sua distanza dal sole dev’essere pari a tre semidiametri dell’orbita terrestre, per cui questo astro potrebbe essere benissimo un nuovo pianeta la cui orbita si troverebbe tra quella di Giove e quella di Marte. È da ritenere che l’orbita di questo pianeta, a differenza degli altri, abbia una notevole eccentricità [...] e che quindi l’ipotesi di un’orbita circolare che io ho fatto sia inadeguata per determinare correttamente dopo tanto tempo il suo movimento e la sua posizione geocentrica. Dobbiamo perciò aspettare le ulteriori osservazioni di Piazzi che egli certamente avrà fatto. [...] Intanto mi auguro che questa lettera le arrivi molto presto e ancora prima che l’astro si perda nella luce del sole; forse Lei, grazie ai suoi strumenti migliori, sarà così fortunato da individuarlo e informarmi con notizie più precise. (Oriani to von Zach, 7 April 1801, in Monatlische Correspondenz … pp. 607–609). 16 … cher ami, j’ai cherché d’après vos élements la planète mais il était déjà trop tard et l’Astre déjà plongé dans les rayons du soleil et dans les vapeurs de l’horizon. Je l’ai cherché inutilement

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Fig. 5.7 Portrait of Franz Xaver von Zach (From Wikimedia Commons)

The Reactions of the International Astronomers’ Community As Oriani fears, Piazzi is soon in trouble. When the news starts to circulate, astronomers expect an official announcement by Piazzi. Why doesn’t he communicate the news? Why doesn’t he provide the data of his observations, so that others could confirm his discovery? Piazzi declares that he is ill. Is it true? It is certainly possible that the stress of the situation affected his health. Nevertheless, suspicions, criticism, and disapproval spread through the international astronomical community. In England, the Astronomer Royal, Nevil Maskelyne, is sarcastic: There is great astronomical news. Mr. Piazzi … discovered a new planet at the beginning of this year, and was so covetous as to keep this delicious morsel to himself for six weeks; when he was punished for his illiberality by a fit of sickness, by which means he lost track of it. […] It will not be so easy to recover […] this having been only a star of the 8 th at first, and now for some months to come not bigger than the 10th or 12th will not be easily distinguished among 40,000 or 50,000 stars of similar appearance as it can be only known by its motion, which cannot be seen immediately but requires observations of the plusieurs belles soirées, Bode me mande qu’il n’avait pas été heureux non plus […] Je vous supplie donc de m’envoyer des élements lorsque vous en aurez de plus correctes car il sera difficile de trouver un si petit astre dans le crépuscule, si sa position n’est pas tant soit peu exacte, et il faudra attendre trop longtemps pour pouvoir l’observer au méridien, je voudrais l’attrapper le plus tôt possible. (Von Zach to Oriani, 29 May 1801, in Foderà and Chinnici 2001, pp. 16–17).

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relative position of several stars among which it is to be looked for. What a deal this imprudent Astronomer has to answer for! It is now publicly proposed in a German publication to all Astronomers in Europe to hunt for it.17

In Germany, von Zach is furious: I cannot but exhale bile against Pazzo (=Crazy). It is truly unpardonable that [he] has made a secret of his discovery for such a long time. If he prevented the astronomers in time, we would know what it is, because we could have observed his planet, his star, his comet, his chimera, all along the months of March and April... All astronomers found his conduct and secrecy very reprehensible, the Parisian astronomers are very angry [including Laplace]. What puerility to keep a secret of his observations until he had calculated an orbit! […] my friend Burckhardt has calculated on the whole of the data of Piazzi’s observations an elliptical orbit of the so-called planet … I have printed as soon as possible a map where the path of the planet is tracked until September. Since, due to injustified jealousy of Piazzi, we have been deprived of the information which would have allowed us to declare the nature of this object, we just have to do a hunt and to field all astronomers and amateur astronomers to chase down, upon its return from the Sun, this pseudoplanet which has the appearance of comet as the toads have appearance of frogs. I regret in advance that I have to waste time searching for it, to tell you the truth, I’m already disgusted [but] we will hunt for this small object, although I’m afraid we will not find anything, it will be nestled, and if indeed this comet or planet will not be found anymore, a shower of reproaches will pour over Mr Pazzo (=Crazy) for doing the mysterious. The most insulting speculations will flow...18

In France, Lalande is doubtful, also due to the attitude of Piazzi, who writes to him: Many astronomers believe that this is a planet; I am still unconvinced.19

17

Maskelyne, June 1801, in House 1989, p. 186. Je ne peux […] [qu’] exhaler mon fiel […] contre Pazzo. Vraiment c’est impardonnable que [celui] ait si longtemps fait un secret de sa découverte. S’il avait averti les astronomes à temps, nous saurions à quoi nous en tenir, car on aurait pu observer sa planète, son astre, sa comète, sa chimère, tout le mois de Mars et d’Avril, et on saurait à présent ce que c’est. Tous les astronomes trouvent sa conduite et ses mystères très répréhensibles, les astronomes parisiens sont bien fachés, et je viens de recevoir une lettre du sénateur Laplace qui pense de même. Quelle puérilité encore de vouloir faire un secret des observations jusqu’à ce qu’il aura calculé une orbite! […] mon ami Burckardt a calculé sur l’ensemble des observations de Piazzi une orbite elliptique de la soi-disant planète […] j’ai fait cito citissime graver une petite carte sur laquelle se trouve la marche future de la planète jusqu’au mois de septembre.

18

Puisque la jalousie malplacée de Piazzi nous a privé des connaissances qui nous auraient faire prononcer sur le nature de cet astre, il nous reste donc que de faire une chasse exacte, et de mettre en campagne tous les astronomes et amateurs pour rattraper sur son retour du soleil cette pseudo planète qui fait visage de comète comme les crapauds font visages de grenouilles. […] Je regrette déjà d’avance le temps que j’irais perdre en [la] cherchant, à dire le vrai, je suis déjà dégouté, […] nous allons donner la chasse à ce petit astre, mais je crains que nous trouverons rien, [elle] aura denichée et si effectivement on retrouve plus cette comète ou planète, le reproche ne manqueront pas de pleuvoir sur signor Pazzo, d’avoir fait le mistérieux. Les conjectures même injurieuses iront leur train… (von Zach to Oriani, 6 July 1801, in Foderà and Chinnici 2001, p. 17). 19 Plusieurs astronomes croient que c’est une planète; j’en doute encore (Lalande 1803, p. 455).

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Fig. 5.8 Portrait of Carl Friedrich Gauss (From Wikimedia Commons)

Piazzi’s Announcement (Too Late) News about the observation of a new planet is circulating, as are the names of Juno and Hera. Piazzi is now anxious to affirm that he is the discoverer. As such, he is the only astronomer entitled to name the new planet, which he rightfully considers “his” planet. In August, Piazzi decided to publish a short report on the new celestial body and to provide the data of the observations. To strengthen the paternity of the discovery, he officially announces the name of the planet: I have hence informed my correspondent astronomers that this new object will be given by me the name of CERES FERDINANDEA.20

Among the correspondents, of course, there is Bode. To stop the discussions about the names and secure his priority, Piazzi writes him a letter in which he clearly states:

20

Ho quindi prevenuti gli Astronomi miei corrispondenti, che sarà da me denominato questo nuovo Astro CERES FERDINANDEA (Piazzi 1801, p. 19).

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I embrace you heartily for having announced the discovery of my new planet, to which I would like to be given the name of CERES FERDINANDEA.21

At this point, it is true that Ceres is lost, immersed in the sunlight, but the data about its observations are now available. Is it possible to try to calculate the orbital parameters to predict its position when it will be visible again? Not exactly. The coordinates provided by Piazzi cover a small arc of the orbit. It is a serious mathematical challenge to try to reconstruct an elliptic orbit with a sufficient degree of precision with so few observations (about twenty). Excellent mathematicians, as Burckhardt, try to do so, but the results are far from being good enough to successfully retrieve the faint new planet among the stars. The situation is discouraging: nobody can confirm the discovery. A tedious, meticulous and time-consuming survey of the sky is necessary. The sarcasm of Maskelyne and the fury of von Zach appear justified.

A “Deus Ex Machina” To solve the complex mathematical problem of calculating an elliptical orbit with few near points is a matter of genius. Hence, a genius comes on stage. Friedrich Gauss (Fig. 5.8), a young and brilliant mathematician, recognizes that this astronomical problem of capital importance can be used to test the application of some mathematical methods he is developing. Nowhere in the annals of astronomy do we meet with so great an opportunity […] than in this crisis and urgent necessity, when all hope of discovering in the heavens this planetary atom, among innumerable small stars after the lapse of nearly a year, rested solely upon a sufficiently approximate knowledge of its orbit to be based upon these very few observations. Could I ever find a more seasonable opportunity to test the practical value of my conceptions, than now in employing them for the determination of the orbit of the planet Ceres, which during these forty-one days had described a geocentric arc of only three degrees, and, after a lapse of a year, must be looked for in a region of the heavens very remote from that in which it was last seen?22

The problem of retrieving Ceres is, therefore, the perfect circumstance for:

21

L’abbraccio di tutto cuore per aver annunciato la scoperta del mio nuovo Pianeta, al quale vorrei veder assegnato il nome di CERES FERDINANDEA. (Piazzi to Bode, 1 Aug 1801, in Bode 1802, p. 35). 22 Nullibi sane in annalibus astronomiae occasionem tam grauem reperimus, […] quam tunc in tanto discrimine vrgenteque necessitate, ubi omnes spes, atomum planetariam post annum fere elapsum in coelis inter innumeras stellulas reinueniendi, vnite pendebat ab orbitae cognition satis approximate, solis illis pauculis obseruationibus superstruenda. Vmquamne opportunius experiri potuissem, ecquid valeant ideolae meae ad vsum practicum, quam si tunc istis ad determinationem orbitae Cereris vterer, qui planeta inter 41 illos dies geocentrice arcum trium tantummodo graduum descripserat, et post annum elapsum in coeli plaga longissime illinc remota indagari debebat? (Gauss 1809 pp. VIII–IX).

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Fig. 5.9 Gauss’orbit (Bode, 1802)

[determining] the orbit of a heavenly body, without any hypothetical assumption, from observations not embracing a great period of time and not allowing a selection, with a view to the application of special methods …23

In October, Gauss offers a set of orbital parameters to the astronomers to retrieve Ceres (Fig. 5.9). Gauss’ orbital parameters are very promising, as they fit Piazzi’s observations better than any other calculated orbit. Von Zach writes to Bode: [These elements] are important because they show that the location of the planet differs 6° to 7° from the orbital elements thus far obtained, as well as from Burckardt’s ellipse. We

23

Determinare orbitam corporis coelestis, absque omni suppositione hypothetica, ex obseruationibus tempus haud magnum complectentibus neque adeo delectum, pro applicatione methodorum specialium, patientibus … (Gauss 1809 pp. VII–VIII).

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just need to expand the exploration area in the sky as eastwards as possible. […] we cannot say other than this ellipse is perfect.24

In France, Lalande is still skeptical; he writes later: In October, Dr. Gauss succeeded in representing all the observations of Mr. Piazzi … on 6 December [von Zach] wrote me that Schroeter, Bode, Olbers and he himself were fruitlessly looking for it … However, I continued to doubt the existence of the planet: the space between the observations was too short; and it seemed to me that a comet eventually perturbed […] by external attractions could describe the observed arc; I could not believe in the existence of a planet which was so small and unnoticed before.25

The promising orbit fulfils the astronomers’ expectations: … the first clear night, in which the planet was searched on the basis of thus deducted calculations, restored the fugitive to observation.26

The first who observes Ceres is von Zach, in December 1801, followed in January 1802 by Bode and Olbers and then in February by French astronomers Méchain and Delambre. Last, Piazzi also reobserves “his” planet (Fig. 5.10): On 23 February, at last there was a very beautiful night, during which I searched for Ceres by using Gauss’ elements, and I soon succeeded in finding it...27 I accept with great pleasure the name of Ceres Ferdinandea [...] You have discovered it in Taurus, and it was reobserved in Virgo, Ceres of the old times. These two constellations are symbols of agriculture. This occurrence is quite unique.28

Consequently, the German astronomer proposes for Ceres an astronomical symbol similar to a sickle. Then, he admits: The name of Juno, or Hera, taken from so a splendid Goddess seems […] quite inappropriate for this small and often invisible Planet.29

24

Von Zach to Bode, 16 Nov 1801 in Bode (1802), p. 58 (here translated from German). Au mois d’octobre, M. le docteur Gauss […] vint à bout de représenter […] toutes les observations de M. Piazzi […] Le 6 décembre [von Zach] m’écrivait que MM. Schroeter, Bode, Olbers et lui cherchaient inutilement […] Cependant je continuais à douter de l’existence de la planète: l’intervalle des observations était trop court; et une comète dérangée, comme celle de 1770, par des attractions étrangères, me semblait pouvoir décrire l’arc observé; je ne pouvais pas croire à une planète si petite, et qui n’avait jamais été remarquée. (Lalande 1802, pp. 456–457). 26 … primaque nox serena, ubi planeta ad normam numerorum inde deductorum quaesitus est, transfugam obseruationibus reddidit. (Gauss 1809, p. IX). 27 Li 23 febbrajo finalmente si ebbe una bellissima notte, nella quale, avendo cercato Cerere cogli elementi di Gauss, mi riesci di subito ritrovarla ... (Piazzi to Oriani, 12 Mar 1802, in Corrispondenza astronomica … p. 62). 28 Accetto con molto piacere il nome di Cerere Ferdinandea [...] Voi l’avete scoperta nel Toro, ed è stata riveduta nella Vergine, la Cerere dell’Antichità. Queste due costellazioni sono il simbolo dell’Agricoltura. L’accidente è molto singolare. (Bode to Piazzi, 26 Jan 1802, in Piazzi 1802, p. 59). 29 Bode 1802, p. 93; original text in German. 25

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Fig. 5.10 First page of Piazzi’s booklet on the discovery of Ceres (Piazzi, 1802)

A Happy Ending: Triumph for Palermo Observatory … and for the German “Hunters”! Piazzi’s honor is now restored, and Palermo Observatory gains scientific reputation: The name of Ceres will remain indissolubly connected to the Sicilian observatory where the discovery occurred (Fig. 5.11). German astronomers of Lilienthal society are also happy: Ceres perfectly fills the gap in the Sun-planets distance, in the expected position indicated by the Titius-Bode law. They were right, in the end. Bode publishes a long and detailed report30 about the discovery and reconstructs the sequence of events (Fig. 5.12). And everyone lives happily ever after. End of story? 30

Bode (1802).

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Fig. 5.11 Engraving reproducing Ceres and the Ramsden Circle, with symbols of the city of Palermo (Piazzi, 1803)

A Sort of Sequel … In March 1802, Olbers discovers another small planet, Pallas. It is very similar to Ceres in size and eccentricity and orbits in the same region of space delimited by the orbits of Mars and Jupiter. These similarities stimulate William Herschel (Fig. 5.13), discoverer of Uranus, to make some considerations. In May, he presents a memoir to the Royal Society of London and argues that we are in front of a new class of celestial bodies, for which he proposes the name of “asteroids”.31 He knows Piazzi, who visited his observatory while staying in London and was in correspondence with him;32 he hence decides to personally inform him about his memoir: … I say in my paper “that the interesting discoveries of Mr. Piazzi and Olbers have introduced to our acquaintance a new species of celestial bodies, with which hitherto we have not been acquainted” … […] From this their asteroidical or starlike appearance I take my name, and call these new celestial bodies Asteroids: so that Planets, Asteroids and Comets will make three distinct species of celestial bodies.33

Herschel hastens to clarify that he does not want to diminish Piazzi’s discovery; on the contrary, he wants to give it more relevance:

31

See Herschel 1802. See Chinnici 2020. 33 Herschel to Piazzi, 22 May 1802 in Corrispondenza astronomica … p. 62. 32

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Fig. 5.12 First page of Bode’s booklet on the discovery of Ceres (Bode, 1802)

To be the first who made us acquainted with a new species of primary bodies is certainly more meritorious than merely to add what, if it were called planet, must stand in a very inferior situation of smallness …34

Piazzi, however, does not take it well; he annotates the letter by Herschel with the words: We’ll soon see Counts, Dukes and Marquises in the heavens too …35 He expresses his disagreement writing to Oriani:

34

Ibid. Presto vedremo dei conti, duchi e marchesi anche in cielo … (Annotation by Piazzi in the letter sent to him by Herschel, ibid.)

35

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Fig. 5.13 Portrait of William Herschel (Museo della Specola, INAF–Osservatorio Astronomico di Palermo & Sistema Museale di Ateneo, Università di Palermo)

Are they wandering stars? If so, let them be called planetoids or competoids, but never asteroids. [...] If an Asteroid Ceres must be called, then so must also be called Uranus...36

Oriani reassures Piazzi: Herschel’s ideas about the two new planets are quite odd. No astronomer finds them acceptable and Zach in his journal has rejected them…37

Nevertheless, the name asteroids will enter into common use in English and, little by little, in other languages: in French, “petites planètes” will be replaced by “astéroïdes” and in Italian, “pianetini” with “asteroidi”. 36

Sono esse stelle erranti? Si chiamino dunque planetoides o cometoides, mai però asteroides […] Se Asteroide deve chiamarsi Cerere, così dovrà pure chiamarsi Urano… (Piazzi to Oriani, 2 July 1802, in Corrispondenza astronomica … p. 62). 37 Le idee di Herschel sui due nuovi pianeti sono bizzarre. Nessun astronomo le trova adottabili e Zach nel suo giornale le ha rigettate… (Oriani to Piazzi, 1 Sept 1802, in Corrispondenza astronomica … p. 63).

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Never say never, however, because in 2006, the International Astronomical Union will classify Ceres as a dwarf planet. Piazzi’s claims are vindicated! On the other hand, for the German astronomers, neither Ceres nor Pallas are large enough to be considered the missing planet: they are rather as fragments of a large planet, called Phaeton, destroyed by some impact or gravitational effects. Consequently, German astronomers continue to “capture” asteroids: in 1804, Harding discovered Juno, and in 1807, Olbers observed Vesta for the first time. After a long fruitless interval of time, the Berlin Academy of Sciences will sponsor the redaction of accurate and updated star charts.38 The survey will restart, and German astronomers will be confirmed to be leaders in asteroid hunting in the nineteenth century.

Piazzi’s Legacy In 1817, Piazzi was called by King Ferdinand to supervise the construction of a new, large observatory in Naples on Capodimonte Hill. He leaves Palermo definitely and lives in Naples in his final years. Nobody else in Palermo will discover new asteroids after him. Starting in the 1860s, the Observatory developed research on solar spectroscopy while planetary astronomy as well as astrometric studies declined for various reasons. Minor contributions from astronomers of Palermo Observatory are the discovery of a comet in 189039 and the first spectroscopic observation of the transit of Venus in 1874, when absorption lines attributed to the planet’s atmosphere are observed.40 Other minor although interesting planetary studies carried out in Palermo deserve further investigation. In contrast, astronomers at the Capodimonte Observatory will work in line with Piazzi’s legacy and largely contribute to extending the list of asteroids in the nineteenth century:41 no less than nine asteroids will be discovered at the Capodimonte Observatory, while over a total of approximately thirty asteroids will be discovered by Italian astronomers in the years 1801–1910 (see Appendix). Notably, asteroids nos. 998, 999 and 1000, discovered in 1923, were called Bodea, Zachia and Piazzia, respectively: the protagonists of the “scientific comedy” of the discovery of Ceres were thus honored in the most appropriate way!

38

See Wolfschmidt in Chinnici 2022b, p. 153. See Chinnici 2015a, pp. 148–149. 40 See Chinnici 2003; Pigatto and Zanini 2001 41 See Gargano and Palma 2020. 39

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Appendix-List of Asteroids Discovered by Italian Astronomers from 1801 to 1910 Name

Year

Discoverer

Observatory

Ceres

1801

G. Piazzi

Palermo

Hygieia

1849

A. De Gasparis

Capodimonte

Parthenope Egeria

1850

A. De Gasparis

Capodimonte

Eunomia Psyche Massalia

1851

A. De Gasparis

Capodimonte

Themis

1853

A. De Gasparis

Capodimonte

Ausonia

1861

A. De Gasparis

Capodimonte

Esperia

1861

G. V. Schiaparelli

Brera (Milan)

Beatrix

1865

A. De Gasparis

Capodimonte

Josephina Unitas

1891

E. Millosevich

Collegio Romano

Tisiphone

1901

L. Carnera & M. Wolf

Potsdam

Argentina Kilia Roma Hedwig Italia Tergeste Caprera Merxia

1901

L. Carnera

Potsdam

Hansa

1902

L. Carnera & M. Wolf

Potsdam

Emita Genua Cremona Venetia Kreusa Comacina

1902

L. Carnera

Potsdam

Interamnia

1910

V. Cerulli

Collurania (Teramo)

References Bode, J. E. (1802). Von dem neuen, zwischen Mars und Jupiter entdecken achten Hauptplaneten des Sonnensystem. Berlin. Chinnici, I. (2003). Transito di Venere 1874: Una spedizione italiana in Bengala. Giornale di Astronomia, 29(4), 45–53.

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Chinnici, I. (2009). The Relationship between the Ramsden Circles at Palermo and Dunsink. Journal for the History of Astronomy, XL, 321–333. Chinnici, I. (2015a). Cerere Ferdinandea. La scoperta del primo asteroide (ora pianeta nano) nelle collezioni storiche dell’Osservatorio di Palermo, INAF-Osservatorio Astronomico di Palermo, Palermo. Chinnici, I. (2015b). Nineteenth-century comets: Studies and observations in Sicily. Journal for the History of Astronomy, 46(2), 130–158. Chinnici, I. (2022a). Una lettera tra gli scaffali: William Herschel a Giuseppe Piazzi. Giornale di Astronomia, 48(3), 45–48. Chinnici, I. (ed.). (2022b). Cosmic Pages. Star Atlases in Italian Astronomical Observatories, Arte’m, Napoli. Chinnici, I., & Foderà, G. (2001). Cerere Ferdinandea, Palerme 1er janvier 1801. L’Astronomie, 115, 2–16. Chinnici, I., Foderà Serio G., & Brenni, P. (2001). The Ramsden’s Circle at the Palermo Astronomical Observatory. Bulletin of the Scientific Instrument Society, 71, 2–10. Coniglio, M., Chinnici, I., & Randazzo, D. (2020). Urania Ferdinandea: la fondazione dell’Osservatorio Astronomico di Palermo. Palermo, INAF-Osservatorio Astronomico di Palermo ISBN: 978–88–87905–09–0 (E-book). Cunningham, C. (2016). Discovery of the first asteroid, Ceres. Historical studies in asteroid research. Springer. D’Andrea, D. (2006). Great Britain and the Mediterranean islands in the Napoleonic Wars—the “insular strategy” of Gould Francis Leckie. Journal of Mediterranean Studies, 16(1/2), 79–90. Foderà Serio, G. (1993). On the history of the Palermo astronomical observatory 2015. In J. Linsky, & S. Serio (Eds.), Physics of solar and stellar coronae (p. 21). Kluwer Academic Publishers. Foderà, G., & Chinnici, I. (2001). Cerere Ferdinandea. Giornale di Astronomia, 28(1), 8–23. Gargano, M., & Palma, P. (2020). Annibale De Gasparis, il giardiniere del cielo di Napoli. Giornale di Astronomia, 46(3), 4–13 Gauss, C. F. (1809). Theoria motus corporum coelestium. Hamburg. Herschel, F. W. (1802). Observations on the two lately discovered celestial bodies. Philosophical Transactions of the Royal Society, 92, 213–232. Howse, D. (1989). Nevil Maskelyne. Cambridge University Press. Invernizzi, L., Manara A., & Sicoli, P. (2001). L’ astronomo valtellinese Giuseppe Piazzi e la scoperta di Cerere. Fondazione Credito Valtellinese no. 11. Lalande, J. (1803). Connoissance des Tems à l’usage des Astronomes et des Navigateurs pour l’an XIII, 1803. Maineri B. E. (1871). L’astronomo Giuseppe Piazzi: notizie biografiche, Milano. Piazzi, G., & Oriani, B. (1874). Corrispondenza Astronomica tra Giuseppe Piazzi e Barnaba Oriani, Pubblicazioni del R. Osservatorio di Brera in Milano, vol. 6, Hoepli. Piazzi, G. (1792). Della Specola Astronomica di Palermo. Palermo. Piazzi, G. (1801). Risultati delle osservazioni della nuova stella scoperta il dì 1. gennajo all’Osservatorio Reale di Palermo. Palermo. Piazzi, G. (1802). Della scoperta del nuovo pianeta Cerere Ferdinandea. Palermo. Piazzi, G. (1803). Praecipuarum Stellarum Positiones Mediae. Palermo. Pigatto, L., & Zanini, V. (2001). Spectroscopic observations of the 1874 Transit of Venus: The Italian party at Muddapur, eastern India. Journal of Astronomical History and Heritage, 4, 43–58. Zach (von). (1801). Monatliche Correspondenz, vol. III-IV. Gotha.

Chapter 6

Catania Observatory and the Italian Contribution to the Measurement of Eros’ Parallax Manuela Coniglio

Abstract Catania Observatory was the only Italian institution participating in the Carte du Ciel project, an international enterprise aimed at producing a photographic map of the sky. In 1900, the photographic plates of the project were used for measuring the parallax of Eros and, consequently, to improve the calculation of the Sun-Earth distance.

The Carte Du Ciel: An International Astronomical Project At the end of the nineteenth century, the French Académie des Sciences promoted an ambitious and demanding astronomical project that was announced on the occasion of the first International Astrophotographic Congress, held in Paris in April 1887 and in which approximately 50 astronomers took part from all over the world. The project, strongly desired and supported by Admiral Ernest Mouchez (1821–1892), astronomer and director of the Paris Astronomical Observatory, was international in scope and aimed at cataloguing and mapping the positions of millions of stars by means of photography. In fact, in those years, the use of photography in astronomy gave excellent results, and it was promising to apply the innovative photographic process on dry plates for the creation of star maps by photographing the sky and measuring the coordinates of the stars on the photographic plates. The new photographic method made it possible to identify stars having higher magnitudes than those visible with telescopic observations and, in principle, to reduce the position errors deriving from usual meridian circle and transit instrument observations. During the Congress, which was attended by the directors of the major observatories, an executive committee and a permanent commission were established to carry out the project, which took the name of Carte du Ciel.1

1

On the origin and development of the project, see Chinnici (2008) and Chinnici (2022).

M. Coniglio (B) INAF-Osservatorio Astronomico di Palermo, Palermo, Italy e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_6

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Fig. 6.1 a The observatories involved in the Carte du Ciel for the astrophotographic catalogue b. The observatories involved in the Carte du Ciel for the sky chart (from a dedicated webpage by D. Randazzo: astropa.inaf.it/carte-du-ciel/)

It intended to be -as indeed it was- the first astronomical cooperative project on a global scale, thanks to the participation of observing stations located all over the world, under the supervision of the Paris Observatory. Approximately twenty observatories joined the enterprise, some of which passed the baton over the years, for a total of 22 participants; each of them was assigned one of the 18 zones of different declinations into which the sky was divided 2 (Fig. 1a, b). To cover the entire celestial vault overall, the observation stations acquired two sets of photographic plates, for a total of approximately 22,000 plates, to obtain a sky chart and an astrophotographic catalogue. The Chart should have included stars up to magnitude 14, the Catalogue should have contained stars up to magnitude 11, sometimes extended up to magnitude 13 according to a precise recommendation given 2

On the participation of various international observatories, see Chinnici (1999).

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Fig. 6.1 (continued)

during the 1889 meeting, intended to favor the search for asteroids.3 A time commitment of approximately six years was estimated. The most complete and accurate astrophotographic chart and catalogue ever created would have been derived from this impressive photographic campaign jointly conducted (Figs. 6.2 and 6.3). To standardize the work of the different observatories and, above all, to obtain homogeneity in the results, it was decided to use the same type of instrument: the astrograph designed in 1880 by the brothers Paul and Prosper Henry, astronomers, opticians, telescope builders at the Paris Observatory and pioneers of astrophotography. The mechanical part of the telescope and the macro micrometer for measuring the plates in the catalogue were made by Paul Gautier.

3

S. V. Débarbat, “Une enterprise internationale d’avant le Service International des Latitudes: la Carte du Ciel”, in Storia del servizio internazionale delle latitudini e delle imprese di cooperazione internazionale (1850–1950) & astronomia e archeoastronomia, a cura di Caledda and E. Proverbio (1999), p. 119.

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Fig. 6.2 Postcard of the Royal Observatory of Catania, with Mount Etna in the background (INAFOsservatorio Astrofisico di Catania, historical archive) Fig. 6.3 Steinheil photographic lens of the Catania Observatory (INAF-Osservatorio Astrofisico di Catania, museum collection)

After taking the photographs, for the Catalogue, the next phase of the work effectively the most demanding of the project consisted of measuring the stellar coordinates on the plates, converting them into equatorial coordinates, reducing them to the year 1900 and publishing the results, whereas for the Chart, it consisted of reproducing by heliogravure the photographic plates on copper plates and then printing them on thick paper. The Carte du Ciel project, born under the best auspices and with the noblest intentions, was actually underestimated in terms of costs, timing and practices: only the Catalogue was in the end achieved, whereas the Sky Chart remained incomplete.

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The International Astronomical Union (IAU), during the 14th General Assembly held in Brighton (United Kingdom) in 1970, declared the partial failure of the project: the President of Commission 23 (Carte du Ciel), Paul Couderc from Paris Observatory, identified multiple causes: for instance, interruptions of the photographic work due to technical problems; lack of human resources to be employed in the required activities; and unsustainable expenses for printing the charts. For these reasons, we must also add the spread of the two world conflicts, which slowed down and, in some cases, definitively blocked the progress of the work. Moreover, the technological and scientific advancement later made its continuation obsolete.4 The Astrophotographic Catalogue, on the other hand, was declared achieved by the IAU in 1964, when the last of the more than 200 volumes containing data on approximately 4.5 million stars was finally published.

The Participation of the Catania Astrophysical Observatory The only Italian institution to take part in the photographic work for the carte du Ciel was the Catania Observatory. The Observatory was established at the end of the 1870s to carry out solar spectroscopic observations on Mount Etna, and its main activity was therefore not linked to astrometry and positional astronomy but to astrophysics.5 In 1876, under the impulse of Pietro Tacchini (1838–1905), adjoint astronomer at Palermo Observatory, an astronomical and meteorological station on Etna was planned, and a few years later, in 1880, the construction operations of the observatory on the southern slope of the Sicilian volcano were completed. The station was equipped with a large Merz refractor having a 33-cm objective lens with an equatorial mounting made by Cavinato in Padua.6 Soon, however, the need to set up a branch in the city emerged, since the difficulties of reaching the station on Etna and the often-prohibitive weather conditions prevented regular observation activity. Therefore, Tacchini proposed to build an observatory downtown in Catania, which was completed in 1885 and located in a former Benedictine monastery, whose spaces were made available by the Municipality. Due to the kind of research that it was conceived for, it took the name of Astrophysical (instead of Astronomical) Observatory, the first in Italy with this denomination. The Observatory on Etna was progressively abandoned: it slowed down its activity until its definitive closure and transformation into a volcanological station. In 1890, not by chance, the first Italian chair of Astrophysics was established in Catania and assigned to Annibale Riccò (1844–1919), who, simultaneously with his teaching assignment, also acquired the position of director of the Catania Observatory. Tacchini, who had taken part in the first Astrographic Congress in Paris, understood the importance of the Carte du Ciel project and supported the involvement of 4

For further information on the Carte du Ciel project, see Lamy (2008). On the history of Catania Observatory, see Chinnici and Blanco (2011). 6 On the telescopes of Catania Observatory, see Orlando (2017). 5

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the Catania Observatory, both for its geographical position and favorable climatic conditions. Moreover, its participation was an excellent opportunity to gain international visibility as well as to acquire new cutting-edge equipment. On the basis of the excellent observational results achieved in the institute’s few years of activity, Tacchini promoted the participation of Catania Observatory in the project and wrote to Mouchez: I would propose to my government to give the Observatory the means necessary to carry out a part of the work. The Catania Observatory is the southernmost one in Europe, and the atmosphere is pure (January 24, 1886).7

The Italian government at first welcomed the proposal to financially support the Catania Observatory, which managed to purchase a photographic equatorial telescope and to build a photographic pavilion. However, the price of the Henry brothers’ telescope, which amounted to 29,000 francs, was considered unacceptable by the Italian government. To contain the costs, the various parts of the instrument were commissioned to different firms: Salmoiraghi in Milan made the equatorial mounting, Audisio in Turin produced the 8-m diameter dome, and the 33-cm aperture objective lens was built by Steinheil in Munich. The telescope was then installed in the pavilion built in the garden near the Benedictine Monastery. The feat was achieved using an astrograph installed in the garden near the Monastery and equipped with a Steinheil lens with an aperture of 33 cm and a Salmoiraghi mount.8

In 1889, on the occasion of the second Astrographic Conference in Paris, Tacchini confirmed the participation of the Catania Observatory, and the sky area between + 6° and +12° of declination was assigned to the Sicilian institution. In the third conference, held in 1891, being director of a participant observatory, Riccò was admitted among the members of the committee by the Bureau du Comité International Permanent pour l’Execution Photographique de la Carte du Ciel. Despite the promises of regular and sufficient funding from the Italian government, however, participation in the project had to deal with the scarcity of funds actually available. The result was a physiological slowness, even in starting the operations, so that Catania’s participation was officially sanctioned only in 1892. Further unexpected events of various kinds contributed to aggravating the situation: before the start of the works, there was a remodulation of the assigned sky zones, and a new zone, between 47° and 54°, was attributed to Catania Observatory: this led to important modifications to the instrument that had been designed according to the initial indications. Furthermore, a defect was found in the telescope objective lens, an 7

De ma part […] je proposerai à mon gouvernement de donner les moyens nécessaires à l’Observatoire de Catane pour qu’on puisse faire une partie du travail […] L’Observatoire de Catane est l’Observatoire plus au sud en Europe et l’atmosphère est si bien pure. Tacchini to Mouchez, Citation contained in Chinnici (1999), p. 453. On the participation of the Catania Observatory to the Carte du Ciel project, see Chinnici (1995). 8 L’impresa è stata realizzata utilizzando un astrografo, installato nel giardino vicino al Monastero e dotato di obiettivo Steinheil con apertura di 33 cm e montatura Salmoiraghi. Favaro (1923), pp. 63–74.

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event that further delayed the beginning of the photographic operations. Nevertheless, Riccò managed to present the first photographs during the Astrographic Congress of 1896, and a few years later, he announced that more than half of the photographic work for the Catalogue (1008 plates in total) had already been done. Other adversities followed one another over the years: constant lack of funds, world conflicts, lack of human resources, the sudden death of key figures in the local management of the project, concurrence of other lines of research to be carried out (meteorological, spectroscopic and geodynamical observations, as well as the editorial work for the publication of the Memorie degli Spettroscopisti Italiani), etc. However, the Catania Observatory tried from time to time to overcome these difficulties and bring to completion the work related to the Catalogue, which required a very demanding process. In Catania, in fact, they worked hard to achieve the initial goal of the project, so onerous that it was abandoned by all the other observatories involved in the Carte du Ciel and completed only by the Catania and Helsinki Observatories: the conversion of the Cartesian coordinates of the star positions measured on the plates into celestial equatorial coordinates. Over time, in Catania, the measurement task was performed by various astronomers, including Azeglio Bemporad (1875–1945), Luigi Taffara (1881–1966) and Eugenio De Caro (1899–1954). In 1942, Catania completed the publication of its section of the Astrophotographic Catalogue in eight volumes, containing the coordinates of more than 300,000 stars. As it was established in Brighton in 1970, the work relating to the section of the Chart was never completed. In the end, participation in the project conditioned the activity of the Sicilian Observatory for approximately half a century, preventing the development of astrophysical research for which it was initially established. This also led to a change in denomination of the Catania chair from “Physical Astronomy” to “Astronomy with elements of Geodesy”.

The International Observing Campaign for Measuring the Eros Parallax A few years after the launch of the Carte du Ciel project, on 13 August 1898, a new celestial body was discovered, the asteroid Eros (433). It was independently identified by astronomers August H. P. Charlois (1864–1910) and Carl Gustav Witt (1866–1946) from the observatories in Nice and Berlin, respectively, and it is the largest asteroid of the Near Earth Asteroid (NEA) family. Although it has an average distance from the Earth equal to that of Mars, Eros can reach a distance much closer to our planet than other celestial objects. This made it particularly interesting because, once its orbit was known and its parallax was measured, it was possible to determine the Sun-Earth distance with sufficient precision by applying Kepler’s second law. The context of the impressive international astrophotographic project was appropriate for exploiting one of the periodic approaches of Eros to the Earth, which had to

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occur under particularly favorable observation conditions. The discovery of Charlois and Witt hence gave the input to a new small-size enterprise within the large enterprise of the Carte du Ciel. The first occasion to measure its parallax occurred during the years 1900–1901, as favorable opposition was expected on 30 October 1900. Therefore, during the International Congress in Paris, the Comité International Permanent pour the Exécution Photographique de La Carte du Ciel elaborated a plan for an observational campaign to determine the Earth-Sun distance by measuring Eros’ parallax. The International Conference for the Photographic Chart of the Sky, held in Paris from 19 to 24 July 1900, had as its object to deal not only with the Photographic Chart of the Sky and related subjects but also with the observations of the new planet Eros.9

As established during its fifth meeting on July 19, a special temporary commission was established to coordinate its work. The first circular was issued in August and invited the main observatories to participate in the new enterprise, asking them to communicate their intentions as soon as possible so that the distribution of the work could be promptly planned. As many as 58 observatories scattered throughout the world gave their support, contributing micrometric, heliometric and photographic measurements. Among these observatories, various Italian observatories also responded positively to the initiative. Given the great interest that for the cognition of the solar parallax has the determination of the greatest possible number of positions of the new planet Eros, all the observatories participating in the work of the Celestial Chart, and others, assumed the commitment to observe, measure or photograph the said planet and the stars near which it would have been found along its trajectory.10

In this circumstance, the Organisation des travaux destinés à la determination de la parallaxe solaire au moyen des observations photographiques et visuelles de la planète Eros dans sa prochaine opposition ascertained that the Observatory of Catania would also have participated by producing photographs of the sky zone crossed by the minor planet. The assignment of the task was positively received by the Sicilian Observatory, which was well aware of the scientific importance of this mission: Giovanni Boccardi (1859–1936), appointed by Riccò to supervise the measurement and calculation works and to study the reduction formulas, argued in fact that the observations of Eros would have rendered the results of the other methods for calculating the solar parallax almost useless. Riccò therefore officially undertook to photograph the sky zone covered by Eros’s trajectory with the cooperation of engineer Antonio Mascari 9

Il Congresso Internazionale per la Carta Fotografica del Cielo si è riunito in Parigi dal 19 al 24 luglio 1900: aveva per iscopo di occuparsi non solo della Carta Fotografica del Cielo ed argomenti affini, ma ancora delle osservazioni del nuovo pianeta Eros. Riccò (1900), p. 68. 10 Stante il grandissimo interesse che per la cognizione della parallasse solare ha la determinazione del maggior numero possibile di posizioni del nuovo pianeta Eros, tutti gli osservatori partecipanti al lavoro della Carta Celeste, ed anche altri, assunsero l’impegno di osservare, misurare, o fotografare, il detto pianeta e le stelle presso le quali si sarebbe trovato lungo la sua traiettoria. Riccò (1901), p. 180.

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Fig. 6.4 List of the number of photographs taken at the Catania Observatory, including those showing Eros’ trajectory (Riccò 1901, p. 184)

(1862–1906), his collaborator in Catania. Of course, the Steinheil-Salmoiraghi photographic equatorial was used to capture the photographs relating to the Eros campaign, which in fact were taken in number 78 in the following autumn and winter 1900– 1901. Of the photographs, the best 48 were sent to the Paris Observatory, which kindly undertook the work of measurement and reduction, which for our limited means would have been too onerous11 (Fig. 6.4). A year later, in the third report about the Carte du Ciel work, Riccò added the information that the 48 best photographs we took of the sky zone covered by the planet Eros have already been measured in Paris and that we have already sent the correction table of the relative grid to that Observatory, which must immediately carry out the reduction of the positions of the stars photographed.12 In 1905, with Circular No. 10 of the Documents relatifs a l’organisation des travaux d’observation de la planète Eros, the publication of the results already obtained started. The circular also contained the news that the Paris Observatory has taken charge of the measurements and the reductions of 48 cliches of the Catania Observatory, where the observations were carried out in the zone positioned symmetrically from one side to the other of the trajectory of the planet, and will soon provide the conclusions as it will do with those of the second part of the work.13 11

[…] che infatti furono eseguite in numero di 78 nel successivo autunno ed inverno 1900–1901; delle dette fotografie le 48 migliori sono state inviate all’Osservatorio di Parigi, che ha cortesemente assunto di fare il lavoro di misura e riduzione, che per i nostri mezzi limitati sarebbe stato troppo gravoso. Ibidem. 12 […] aggiungo l’informazione, che le 48 migliori fotografie da noi fatte della zona di cielo percorsa dal pianeta Eros sono state già misurate a Parigi; e che abbiamo già mandato la tavola di correzione del relativo reticolato a quell’Osservatorio, che deve subito eseguire la riduzione delle posizioni delle stelle fotografate. Riccò (1903), p. 27. 13 L’Observatoire de Paris, ayant pris à sa charge les mesures et les réductions de 48 cliqués de l’Observatyoire de Catane, sera également bientôt en état d’en fournir les conclusions ainci que celles de la seconde partie de ses propres travaux. Académie des sciences—France, Paris (1905a), p. 4.

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In the Bulletin du Comité international permanent pour l’exécution photographique de la Carte du Ciel, Circular No. 11 mentioned the results achieved by the observation campaign for the determination of the solar parallax launched at the Paris Astrographic Conference of 1900. The same circular reported the contribution from Catania Observatory due to the observations of Riccò and Mascari: Photographs relating to the area of the sky covered by Eros were taken every evening when the weather permitted. In this way, 47 clichés were obtained. The Paris Observatory was responsible for measuring the coordinates carried out in the two “orientations” 0° and 180°, for determining the constants of the clichés and for converting them into an equatorial position. The reference stars used for the reduction are distributed over the entire extension of the cliché, but only the coordinates of the stars that are included in a space of 10’ on each side of the trajectory of Eros have been detected. The photographic observations of Catania are provided in the form of 3 tables. Table I provides the average position of the reference stars, the seconds of the right ascensions and declinations adopted, and the comparisons and the numbers of the clichés that contain them. Table II contains the coordinates for 1900.0 of the stars included in a space of 10’ on each side of the trajectory followed by Eros. In the end, Table III provides the positions of the comparison stars extracted from Table II. Until December 13, 1900, the poses were 6 and 3 min; after December 13, the poses were 7 and 5 min14 (Fig. 6.5).

In the rest of Italy, other Observatories were involved in this mission, even if there were also some refusals, as in the case of the Brera Observatory, whose director Giovanni Virginio Schiaparelli (1835–1910) declared that there was a lack of an adequate instrument for this kind of observation and that there was superficial knowledge of the phenomenon to be studied. Padua Observatory was engaged in the campaign from 23 October 1900 to 13 February 1901 by using the Dembowski equatorial telescope (Merz refractor) with micrometric observations made by Antonio Maria Antoniazzi (1872–1925) with the transit method (see Antoniazzi 1990). Elia Millosevich (1848–1919) at the Collegio Romano Observatory studied the orbit of the minor planet and collaborated in drafting its Ephemeris; starting from the analysis of the Carte du Ciel photographic plates taken from 1896, he was able to calculate the orbit of Eros. At Capodimonte, the observations of Eros were carried out with a Repsold Meridian Circle (see Contarine 1903). A contribution to the meridian observations of the stars on the journey of Eros (1900) was also given by the Campidoglio Observatory in Rome. Arcetri contributed observations made with the Amici 14

Les photographies relatives à la zone du ciel parcourue par éros ont été faites tous les soirs où le temps l’a permis; on a ainsi obtenu 47 cliqués. L’Observatoire de Paris s’est chargé de la mesure des coordonnées effectuées dans les deux orientations 0° et 180°, de la détermination des constantes des clichés et de leur conversion en positions équatoriales. Les étoiles de repère utilisées pour la réduction se répartissent dans toute l’étendue du cliché, mais on a seulement relevé les coordonnées des étoiles se trouvant comprises dans un espace de 10’ de chaque côté de la trajectoire d’Eros. Les observations photographiques de Catane sont fournies ci-après dans 3 Tableaux. Le Tableau 1 donne les positions moyennes des étoiles de repère, on y a joint les secondes des ascensions droites et des déclinaisons adoptées, les comparaisons et le nombre des clichés qui les contiennent. Le Tableau II renferme les coordonnées pour 1900,0 des étoiles comprises dans un espace de 10’ de chaque côté de la trajectoire suivie par la planète Eros. Enfin le Tableau III donne les positions des étoiles de comparaison extraites du Tableau II. Jusqu’au 13 décembre 1900 les poses étaient de 6 et 3 min; depuis le 13 décembre, les poses ont été de 7 et 5 min. Académie des sciences—France, Paris (1905b), p. 85.

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Fig. 6.5 Page containing the coordinates for 1900.0 of the stars included in a space of 10’ on each side of the trajectory followed by Eros that were measured at the Catania Observatory. (Académie des sciences, 1905b, Tav. II, p. 111)

equatorial telescope, while the Collurania Observatory of Teramo, established just 10 years earlier, contributed thanks to Vincenzo Cerulli (1859–1927), who carried out 352 measurements of right ascension and 172 of declination with a Cooke equatorial refractor.15 The large international participation and collaboration, which also included the Italian Observatories, was very important since it gave the possibility of combining data from stations located all over the planet. In the period 1900–1901, in fact, approximately 60,000 observations (direct or photographic) were obtained; thanks to these data, astronomers from all over the world were able to establish the value of the solar parallax in 8,800 s of arc, thus reaching a degree of accuracy never previously achieved and which is very close to the currently accepted value of 8.79, equal to 149.5 million km. The final results were published in 1910 by Arthur Robert 15

See «Positions équatoriales de la planète Eros obtenues à la vision directe» (Circular No. 12, ibid.).

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Hinks (1873–1945) from Cambridge Observatory, who elaborated the measurement series provided by numerous observatories. The measurement of Eros’ parallax, originating within the large enterprise of the Carte du Ciel, could give excellent results thanks to the scientific network created by each institution: a circumstance that further confirmed what Descartes said in the seventeenth century: I judged that there was no better remedy […] than to communicate to good minds to contribute to further progress, each according to his inclinations and abilities, by setting up the necessary experiments and communicating to the public all that they have learned, so that one man may begin where another left off; thus, by combining the work of many over time, far more progress would be made by all together than anyone could alone.16

In conclusion, even if the Italian contribution to the photographic work of the Carte du Ciel project was limited to the only Observatory of Catania, other Italian observatories were involved in the measurement and calculation works and contributed to the successful campaign for determining Eros’ parallax.

References Académie des sciences. (1905a). Documents relatifs a l’organisation des travaux d’observation de la planete Eros, Circulaire n.10. In Bulletin du Comité international permanent pour l’exécution photographique de la Carte du Ciel, Tomo quatrième. Académie des sciences. (1905b). Documents relatifs a l’organisation des travaux d’observation de la planete Eros, Circulaire n.11. In Bulletin du Comité international permanent pour l’exécution photographique de la Carte du Ciel, Tomo quatrième. Antoniazzi, A. (1990). Il valore medio della parallasse solare risultante dalle osservazioni dei passaggi del pianeta “Eros” fatte all’equatoriale Dembowski dell’Osservatorio di Padova dal 23 ottobre 1900 al 13 febbraio 1901. Premiate Officine Grafiche di C. Ferrari, Venezia. Caledda, P., Proverbio, E. (1999) Storia del servizio internazionale delle latitudini e delle imprese di cooperazione internazionale (1850–1950) & astronomia e archeoastronomia. Cooperativa Universitaria Editrice Cagliaritana. Chinnici I. (1995). Il contributo dell’Italia all’impresa della Carte du Ciel, Giornale di Astronomia (No. 3, pp. 11–22). Chinnici, I. (1999). La Carte du Ciel. Observatoire de Paris, Paris. Osservatorio Astronomico di Palermo G.S. Vaiana, Palermo. Chinnici I. (2008). La Carte du Ciel: genèse, déroulement et issues. In J. Lamy (Ed.) La Carte du Ciel (pp. 19–43). EDP Science. Chinnici I., Blanco C. (2011). L’Etna e le stelle. La nascita dell’Osservatorio Astrofisico di Catania. Società Italiana degli Storici della Fisica e dell’Astronomia: Proceedings of the 33rd Annual Conference.

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Je jugeois qu’il n’y avoit point de meilleur remède […] que de communiquer les bons esprits à tâcher de passer plus outre, en contribuant, chacun selon son inclination et son pouvoir aux expériences qu’il faudroit faire et communiquant aussi au public toutes les choses qu’ils apprendroient, afin que les derniers, commençant où les précédents auroient achevé, et ainsi joignant les vies et les travaux de plusieurs, nous allassions tous ensemble beaucoup plus loin que chacun en particulier ne sauroit faire. R. Descartes (1637), pp. 193–194.

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Contarine, F. (1903). Osservazioni del Pianeta Eros fatte al Circolo Meridiano del R. Osservatorio di Capodimonte durante l’opposizione 1900–1901. Napoli. Descartes, R. (1637). Discours de la méthode pour bien conduire sa raison et chercher la vérité dans les sciences. Sixième Partie. Favaro, G. A. (1923). Cenno necrologico di Annibale Riccò. Annuario Regia Universita Di Catania, 1922–23, 63–74. Lamy J. (2008). La Carte du ciel. EDP Sciences. Orlando A. (2017). A Merz Telescope on Mount Etna: The Catania Astrophysical Observatory. In I. Chinnici (Ed.), Merz Telescopes. A Global Heritage Worth Preserving (pp. 137–156). Springer. Riccò, A. (1900). Memorie degli Spettroscopisti Italiani. XXIX. Riccò, A. (1901). Lavoro della Stazione Internazionale nell’osservatorio di Catania per la carta fotografica del cielo, Seconda relazione. Memorie degli Spettroscopisti Italiani, 300. Riccò, A. (1903). Lavoro della Stazione Internazionale nell’osservatorio di Catania per la carta fotografica del cielo, Relazione III. Memorie degli Spettroscopisti Italiani, XXXII. Tacchini, P. (1878). Della convenienza ed utilità di erigere sull’Etna una Stazione astronomica e meteorological. Atti dell’Accademia Gioenia, ser. III, 12. Turner, H.H. (2009). The great star map, being a brief general account of the international project known as the astrographic chart. Cornell University Library.

Chapter 7

From Earth to the Main Asteroid Belt: The Path of Turin Astronomers in the Exploration of the Solar System Giuseppe Massone

Abstract Through the two and half centuries of his activity, astronomers at Turin Astronomical Observatory have studied the various bodies of the Solar System: starting from the Earth by the geodetic campaign in the eighteenth century, then, thanks to the celestial mechanics, the Moon orbit in the 19th, and finally in the twentieth century, the minor bodies: asteroids and comets, both investigated for determining their classical astrometric parameters and physical structure—not to mention the discovery of some new members.

The First Historical Period When in 1925 at the Turin Astronomical Observatory a new program of photographic determination of accurate minor planets positions started, the institute was in activity for more than a century and a half (a comprehensive historical sketch can be found in Observing the stars, 2009). The beginning of the story (according to the currently accepted tradition) can be pushed back to the year 1759, when Carlo Emanuele III, King of Piedmont, charged father Giovanni Battista Beccaria to measure a meridian arc in his (quite small by then) kingdom. Geodesy was at that time at the peak of popularity among the scientific community, and several similar operations had been conducted or were in progress throughout Europe. Unfortunately, for father Beccaria, who was neither young nor very much pleased with a task fairly outside of his customary activity as a physics professor at Turin University, the outcome of this survey (Beccaria, 1774) turned out to be in complete disagreement with the results of similar surveys abroad. Indeed, the main reason for this disagreement was not a fault to be ascribed to him but rather due to some external factors not yet well understood at that time; however, the publication of the Gradus Taurinensis started a controversy that could be quenched

G. Massone (B) INAF Osservatorio Astrofisico di Torino, Turin, Italy e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_7

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only when the existence of gravitational anomalies of the terrestrial potential were confirmed and fully enlightened. Apart from the geodetic task that he accomplished, it does not seem that father Beccaria worked much on both observational and theoretical astronomy; the same can be said for the two personalities succeeding him at the head of the observatory: father Valperga di Caluso and Antonio Maria Vassalli-Eandi. They were also charged with several appointments unrelated to astronomy, such as the secretariat of the Turin Academy of Science, consultations and teaching activities, in both public and private institutions; therefore, a short time was left for a rather demanding activity such as the conduction in full of an astronomical observatory. Moreover, the furniture of astronomical instruments was quite modest: in addition to the old Beccaria’s geodetic instruments, during the following 30 years, only a 9-cm Dollond refractor was acquired and very sparsely used at the occurrence of some lunar eclipses and occultations. In the meantime, the observatory changed its status from a university institute to an ancillary institution of the Turin Academy of Science (not without sparkling an administrative querelle on respective properties and expenses), moving from its first location to a new site on the roof of the academy palace. The most continuous activity during the observatory’s early years was the collection of meteorological observations.

Giovanni Plana and the New Observatory Site at Palazzo Madama A decisive step in observatory development came with the arrival of Giovanni Plana in Turin. He was a smart fellow, born in a Piedmont province, still proudly celebrated as the most incisive local astronomical personality, but his appointment had been a kind of intricate process. He returned to Turin from Paris after having earned a degree from “Ecole Polytechnique”, where he could take advantage of lessons on mathematics and celestial mechanics by G. L. Lagrange, to cover the position of mathematics professor at the local “Scuola di Artiglieria” in 1803. His strong wish, however, was to teach astronomy at the university, and he was disappointed when, in 1805, the position was assigned to another personality. It was only in 1811 that, thanks to the advice of Lagrange, he was appointed to the astronomy chair. To further complicate the matter, the direction of the observatory was split into two sections (astronomical and meteorological), each assigned to a different person. He could finally take on the directorship of the astronomy section in 1813 and, after a “supplica” to the king in 1815, the title of “Regio Astronomo” (Royal Astronomer). During the first ten years of his tenure, he did his best using the scanty instrumental provision he found at the observatory, but his effort and abilities, not to mention a good “savoir faire”, were soon amply recognized, and with king support, he could obtain funds for new and modern instruments and a new location to move once again to the observatory. The new site (Fig. 7.1) was right in the city center, on the

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roof of the historical Palazzo Madama, and did not meet universal appreciation from colleagues abroad, as someone suggested a more peripheral place; however, at that time, Turin was still a rather small town, and the teaching task at the university and “Scuola di Artiglieria” did not permit the astronomer in charge to reside much farther away. The adaptation of one of the old towers on the new site was almost complete for 1822, when the recently acquired Reichenbach meridian circle was collocated on his pillars and the observations started. For some years, Plana activity was primarily devoted to positional astronomy, with an extensive campaign to determine the accurate latitude and longitude of the new observatory. Meanwhile, geodesy was not neglected as well; a special campaign—carried out during the years from 1821 to 1823 in collaboration with Brera Observatory in Milan and detachments of Piedmont and Austrian army corps of engineers—was planned and carried out to join the respective geodetic networks with the French one across the impervious Alpine environment. (Carlini & Plana, 1825, 1827) (Fig. 7.2) Among the results secured by this survey, there was a complete revision of the so-much-disputed father Beccaria’s meridian arc measurement; it basically confirmed that the disagreement between astronomical and geodetic latitudes was indeed due to local gravitational anomalies. Afterwards, Plana activity switched towards the field of celestial mechanics, and in this field, he achieved the most significant results for which he is mainly remembered and celebrated today. The “Teorie du movement de la Lune”, first published in 1832 in three volumes, was acknowledged as a master’s work and awarded by the French Academy of Science. Plana was a well-known personality in Turin, then the capital city of the Piedmont kingdom, and among the several awards collected during his long life, he was raised to peerage as “baron Plana” by King Carlo Alberto in 1844.

The Need for a New Site for the Observatory Nevertheless, after half a century of operations, the location on the top of the Palazzo Madama had become unsuitable, as it can be inferred by the complaints that Alessandro Dorna, who was appointed director of the observatory after Plana’s death in 1864, addressed the respective assignments to both the university and the new, after the Italian unification in 1861, Ministry of Education. Moreover, Italian unification was a major derangement for the city of Turin because it was stripped of its status as the capital city of the new Kingdom of Italy in favor of Florence and later, Rome, as soon as the process of Italian unification was completed. As a result, for some years, Turin was plagued with a strong economic crisis due to the loss of ten of thousand working positions of the central state agencies and government departments, which were moved as well. To counteract this crisis, city management promoted extensive industrial development to recover lost working positions. After a few years of this cure, the crisis was over, but the environment, from the astronomical point of view, deteriorated because air and light pollution increasingly plagued the observations. Moreover, the main instrumental acquisition secured by Dorna, i.e., a 30 cm Merz refractor, could not be used to its full potential.

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Fig. 7.1 The Observatory of Turin in the nineteenth century, on the roof of Palazzo Madama in the city center (INAF–Osservatorio Astrofisico di Torino, historical archive)

Fig. 7.2 Plan of Turin in 1820 (Opérations Géodésiques et Astronomiques, Tome I, p. 61; INAF– Osservatorio Astrofisico di Torino, library)

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When Francesco Porro took over the direction in 1886 after Dorna’s sudden death, even the instruments for positional astronomy were ill-placed. The perturbations produced by the new tram with tracks laid down in the same square as Palazzo Madama were enough to disrupt the star transit determination at the transit circle if a vehicle was passing in the meanwhile. The search for a new site for the observatory far from the city center became increasingly pivotal. Porro explored a few locations on the hill chain that borders the city of Turin on the east side and went as far to establish on one of these hills a temporary station with a 15-cm telescope of short focal length that was acquired for; however, in spite of his several efforts, he was not able to achieve his dream of establishing a new observatory.

Giovanni Boccardi and the Final Moving in Pino Torinese The final moving of Turin Observatory to its present location in the town of Pino Torinese was due to the effort of Porro’s successor. In 1902, Porro asked to be transferred to fill the chair of astronomy at Genua University and to hold his former position in Turin was called Giovanni Boccardi. This appointment was surprising for the (small by then) Italian astronomical community: a position of professorship in astronomy with the associated direction of an observatory was usually conferred to a well-known candidate who worked for a convenient period in a subordinate position and showed outstanding scientific capabilities and initiative. Giovanni Boccardi was a kind of outsider in this respect: he was a Catholic priest that, after his ordination, chose to become a missionary and was sent (as mathematics professor) to some communities in the Ottoman Empire. It is difficult to say exactly when the interest in astronomy started to attract him; however, during the missionary commitment, latitude and longitude determinations with portable instruments can be found in his notebooks. He was in his thirties when he decided to become a professional scientist and returned to Italy working as an assistant in the Rome, Vatican and Catania observatories. He obtained the position in Turin after a “concorso” in 1902 (he was 43, rather old aged) but soon displayed an energy almost unbelievable in a younger person. The observatory was then almost abandoned; nonetheless, he started new observational programs with the old instruments. Actually, moving outside the city center was his top priority, but he soon encountered countless difficulties and clashed with his opponents, as we can read in his memories: “Nothing more to free the observatory from that slavery was in my mind. I got the opposition of observatory’s staff, of the Science Faculty, of the central office in Rome and even a portion of citizenship, but I did not stop in my path…” (Boccardi, 1930; original text in Italian). He truly pestered with his requests for almost any city and national agency from which he could obtain financial support, and finally, he could see, at the end of 1907 (Fig. 7.3), the beginning of work with the construction of a new access road to the new site. In December 1911, with the main installations almost completed, he was able to start a new program of systematic latitude determination in the new observatory, located on a hill in Pino Torinese, at a height of approximately 600 m, a

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Fig. 7.3 The new observatory site on the top of a hill at Pino Torinese (INAF–Osservatorio Astrofisico di Torino, historical archive)

favourable astronomical site for that epoch. The already available instruments were also moved, and the 30-cm Merz refractor was installed under a new dome; the hill was indeed like an extended ridge of approximately 300 m in length, therefore providing plenty of space for the old and new instruments. The full list at that time included the 30-cm Merz refractor, the new transit instrument of the first vertical, the 15-cm refractor provided by Porro, the old Reichenbach meridian circle and a new transit circle from Bamberg firm. Boccardi was a very passionate observer; if Plana can be considered the best theoretical astronomer in Turin, for sure Boccardi was the most prolific observer. So much work undermined his health, especially when he lost most of the observatory’s staff because of the enlisting during WWI, and consequently, he was forced to cease almost all practical activities in 1922. Father Giovanni Boccardi was devoted through his whole scientific activity to classical astronomy. In addition to his work on star catalogues, either discussing already published data or producing new data by his own observations, his main legacy is related to the study of latitude variations. This was a key problem in fundamental astronomy at the end of the 19th and the beginning of the twentieth centuries, directly related, as it was, to the very basic problem of the definition of the main reference system of astronomical coordinates. The discovery, at the end of 1800, of the so called “polar motion” disseminated a deep discomfort among those who, within the astronomical community, were working on this subject. An international workshop was soon convened, and the main resolution agreed upon was to establish a network of observing stations around the world to continuously monitor the phenomenon by systematic latitude determinations. However, as in most if not all human activities, unanimity is quite impossible to reach: some personalities expressed criticism of either observational programs or methods adopted by the new international network, precursor of the International Latitude Service. Boccardi was one of those characters and, in the new observatory, at top priority for himself, he devised a program of latitude determinations based on different criteria to supplement and crosscheck the

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official ones. He worked relentlessly on it until his health started to seriously deteriorate to the point that, when he asked for retirement in 1923, some year in advance on normal retirement age, he was almost blind. Although the results he claimed to discover were not confirmed afterwards, his legacy was not lost because the Turin Observatory was to become the central office of the International Latitudes Service (ILS) in 1949, where observations from all over the world related to this service were collected and analysed.

Boccardi’s Last Acquisition: The Photographic Telescope One last merit can be ascribed to Father Boccardi before we go further on with our story. The photographic technique was already well established in astronomy as a powerful tool to replace and extend the limit of the human eye in sky exploration; however, at the beginning of the twentieth century, very few Italian astronomical observatories were equipped with photographic telescopes, whereas in some foreign countries, such as the United States or Germany, the photographic technique was already extensively employed. Father Boccardi, probably thanks to his previous experience in Catania and Vatican observatories, both working on the Carte du Ciel program, leap on the still prevailing prejudices about the new technique (one for all, the leading authority on astrometric star catalogues, German astronomer Arthur Auwers assertively stated that using photography instead of the canonical meridian circle to determine star positions was “against nature”) and decided to acquire a photographic telescope. Such an instrument was so a shocking novelty that even a new name for it was minted by Boccardi: the “Euriscopio”, a name that was derived from the Greek language and can be translated as a “large view instrument” due to its larger than usual field of view. To gather the money for the purchase, a public subscription, managed by the local newspaper “La Stampa”, was announced: the response of the citizens of Turin was so generous that Boccardi was truly touched and wrote them a warm message of thanksgiving. He had, however, almost no opportunity to operate his last acquisition for the observatory: his health was steadily declining, and he asked to be relieved from the directorship, only keeping the university position. The ministry instead decided tout court for a full retirement, and, with some regret, he left his loved observatory forever in December 1923. (Fig. 7.4). The new photographic instrument arrived, after some delay, in 1921 and was installed on a new dome in 1922. An 18-cm telescope was initially planned, but thanks to the successful subscription, it was possible to order a larger telescope from the renowned German Zeiss firm, which delivered a 20-cm diameter (with 1 m focal length) three-lenses photographic objective, with a 13-cm (170 cm focal length) guiding telescope, together assembled on an equatorial mounting, equipped with weight-driven sidereal motion. As the original plate holder was suitable for 18 × 24 cm plates, the field of view that could be covered on a single exposure was quite wide: 10 × 13 degrees. The image quality indeed was not uniform over the whole field: it was quite good within the central zone covering approximately half the field

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Fig. 7.4 The Zeiss astrograph after the restoration of 2015 (author’s personal archive)

but worsened toward the plate edges, showing some amount of astigmatism and field curvature. This blemish on Zeiss outcome, however, seems not to have hampered the effort of Turin astronomers for several decades: it had been only after about forty years of use that they decide for a change and ordered, from Zeiss again, a new four-lenses objective, with the same aperture and a slightly longer focal distance of 114 cm, almost matching on the plate the scale of the BD (Bonner Durchmusterung) atlas.

Minor Planet or Asteroid? When in 1925 Luigi Volta was appointed astronomy professor at the University of Turin and took over the associated directorship of the observatory, in almost all Italian astronomical observatories, cometary and minor planet positions were obtained by visual observations. The observer was working in the dome of an equatorial telescope, with a suitable micrometer attached to it. Micrometers were available in different forms and types, from the “filar” micrometer so ubiquitous among double star observers to “bar” and “ring” micrometers, especially designed for observations of faint objects, when the treads of the filar type are almost invisible due to the very low illumination required to see both the celestial object and the reference star

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within the eyepiece field. The position of the target was derived by comparison to (at least one, but sometimes two or more) positions of reference stars taken from the best available catalogues: in right ascension by the differential transit time over the eyepiece’s reference with the telescope sidereal motion stopped; then, the difference in declination was measured with the micrometer screw. The positions were good for orbital computation; however, the limiting magnitude was dictated by the telescope aperture and observer’s visual acuity, and the faintest objects were accessible only to a few observers with the largest instruments. The introduction of photography opened up new possibilities: now, the combination of plate sensitivity, telescope aperture and focal distance (asteroids are moving targets; therefore, their image is not point-like as for stars) all play a role in fixing the magnitude limit. The advantage over visual is high; moreover, as photographic telescopes have a much larger field of view, more than one target can be captured on a single exposition, thus increasing efficiency. (Fig. 7.5). It is perhaps worthwhile here to spend a few words about the astronomical nomenclature of objects within the Solar System: the matter was once more revised by resolution 5 and 6 adopted by IAU general assembly in 2006, which had the effect, among others, to strip Pluto of his rank of planet. Historically, the words “asteroid” and “minor planet” were used interchangeably, at least from 1850 onwards, although “asteroid” was rejected by Giuseppe Piazzi, the discoverer of the first of them, as you may read in another chapter of this book. He proposed instead, in a letter to his friend Barnaba Oriani (Cacciatore and Schiaparelli, 1874), to name them “planetoides” or “cometoides” based on apparent motion similarity. Currently, according

Fig. 7.5 The old 30-cm Merz refractor in 1982 (author’s personal archive)

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to the IAU resolutions, those objects orbiting the Sun for which the categories of “Planet”, “Dwarf Planet” or “Satellite” are not applied shall be collectively referred to as “Small Solar System Bodies”. However, the current situation is fairly more intricate than the past, as we have several classes of these objects, such as “Centaurus” and “Trans-Neptunian”. All the minor planets’ observations are collected at the “Minor Planet Center” (MPC), an institution founded in 1947 under the auspices of the International Astronomical Union (IAU); it operates (from 1978 onwards) at the Smithsonian Astrophysical Observatory, which is part of the Center for Astrophysics along with the Harvard College Observatory. Here, the orbits are calculated, and the information is distributed monthly by the Minor Planet Circulars. The same center also runs an extensive database with several freely available tools to help asteroid and comet observers. As even within the MPC database, the customary synonymy between “minor planet” and “asteroid” is currently retained, we will adhere to it within this chapter as well. When a “new” minor planet is observed for the first time, it receives a provisional name consisting of the year of discovery, followed by a two-letter code. The first letter indicates the half-month of the object’s discovery within that year and runs from A to Y (I is not used to avoid confusion with 1); the second letter indicates the order of discovery within that half month. The final designation, consisting of a numeral and optionally, but not always, a name, is then assigned when a good orbit has been computed. This usually happens after the object has been observed for three or four oppositions. Exceptions may be dangerous or unusual objects, for which the final naming can come after two oppositions only. For example, the object discovered on the night of January 28, 1989, at the Osservatorio San Vittore in Bologna received the provisional name 1989 BF and the final name (4062) Schiaparelli, after the famous Italian astronomer.

Volta’s Photographic Program From the archive records of Volta’s directorship and from reports sent for publication, it appears that observations of comets and minor planets took on a larger share in Turin Observatory than in previous years. For sure it was due to some external factors, in addition to the availability of the new photographic telescope: for instance, once normal postwar conditions were reestablished, the enlisted staff could return at work and two young astronomers were hired: Antonio Ferrero and later Alfonso Fresa. It also appears that Volta, despite his director position, participated with a major role in an activity that was usually committed to subordinates: namely, using the visual technique of observation with the 30-cm Merz refractor and, from 1925 onwards, with the Zeiss astrograph. The reduction of star positions on photographic plates requires its own procedure: this has become a trivial task today as we have plenty of facilities for image analysis and computation, even for free exploiting the web resources, but it was a major problem at that epoch, when everything was to be done manually. Much theoretical and practical experience had already been accumulated after the ongoing undertaking of the Astrographic Catalogue, the international

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enterprise organized by Paris Observatory at the end of the nineteenth century to coordinate eighteen observatories worldwide to catalogue and map the whole sky: nevertheless, the procedures for deriving the position of several stars from the same plate, such as the “plate constant” method proposed by H. H. Turner, were not convenient when just one single object was on aim, and to spare as much computational effort as possible, different approaches had to be considered. One practical solution, the so-called “dependence” method, was proposed by F. Schlesinger at Yale observatory (Schlesinger, 1911, 1926) for the reduction of parallax plates; starting from this method, several adaptations were devised (Volta, 1933; Bemporad, 1935). (Fig. 7.6)The basis of the method was to select on the plate at least three reference stars (four or more were possible, at the cost of increased computation time) surrounding the target; the optimal configuration was with the target close to the barycenter of the triangle having three reference stars as vertices. Then, if a twoscrew measuring machine was available, the simplest option was to measure both x and y coordinates of all four (or more) images; from these measurements, the mutual distances of all images could be computed. If a single screw machine was at hand, the mutual distances between two images could be measured directly, as these were the only data required for computing an object’s unknown position. On plates taken with a short-focus telescope, such as the Zeiss astrograph, a good set of reference stars could usually be found within a small distance –ten to twenty millimetres from the target–therefore requiring a rather short measuring machine screw. From these measures and from the knowledge of what the “guiding star” was (i.e., the star located on the so-called tangent point, namely, the point where the ideally prolonged telescope axis intercepts the celestial sphere), the standard coordinates and then the spherical right ascension and declination of the target could be derived. Photographic observations with the Zeiss astrograph started in 1925. For this task, at least four to five people actively collaborated in the various tasks of preparing the observation program, taking the exposures at the telescope, measuring the plates and performing all the required computations to obtain the final minor planet position. In addition to the director, Luigi Volta, engineer Paolo Vocca, who was a staff astronomer for a long time, and the new entries Ferrero and Fresa, with some contribution from G. B. Lacchini, shared the burden. The starting up was not very rushed: for the first year, only four plates were secured, the first on Aug. 12. Most likely, several details of the novel photographic technique had to be probed to gain some experience, such as selecting a suitable plate supply, choosing the optimum chemicals for development and fixer treatments and then implementing and verifying the whole reduction procedure. After the first two years of training and practice, a more continuous operation went on, as shown in Table 7.1. The method that was adopted for the plate exposure was quite simple: after the sky region to be imaged had been selected (it is unclear on the basis of which criterion the selection was made–whether trying to maximize the number of objects per plate or aiming at targets in more urgent need of observations), a suitable “guiding star” to be placed on the plate center was chosen as well; the same star should have been seen at the eyepiece of the coaligned visual telescope to be used for “guiding”, i.e., to adjust for the residual irregularities of the sidereal motion. Based on my personal

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Fig. 7.6 The Orion belt on a typical photographic plate taken with the Zeiss astrograph in 1936 (INAF–Osservatorio Astrofisico di Torino, plate archive: Zeiss plate taken on January 18, 1936) Table 7.1 Number of photographs taken per year with the Zeiss astrograph during the first 8 years of operations

Year

Plates

1925

4

1926

3

1927

30

1928

37

1929

43

1930

58

1931

61

1932

67

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experience, having used the same telescope during the last fifteen years of the past century, almost all BD stars were accessible to the visual guiding telescope for this task. Just one single plate was obtained during one observing night, but with a very long exposure time, usually ranging from two to three hours, unless some worsening of weather conditions compelled the shutter to be closed. The sensitivity of the plate used was probably not high, as the sky background is generally low. With such a long exposure, a minor planet, due to his orbital motion, was not fixed within the star field: a typical main belt asteroid at the opposition (the most favorable observation’s epoch, as it was at the maximum brightness as well), has a sky motion rate ranging from 0'' .5/min to 1'' /min, therefore leaving on the plate, considering the 1 m focal length of our telescope, a trail of 0.3 up 0.6 mm, whereas the image size, for a nonoverexposed star in the area around plate center, was approximately 0.1 mm (this was one of the reasons that lead to the replacement of the old objective with a new one, which yields star images a factor 2 to 3 smaller) The magnitude limit was approximately 13.0–13.5, quite good for that time, when just commercial photographic plates were available. Once the plate was developed and fixed, all the minor planets were searched for and measured along with their respective comparison stars. As the field covered was quite large, several objects, in some cases up to ten, could usually be found and measured on a single exposure. The data for each minor planet positional computation were noted on a series of notebooks still existing within the observatory archive. The very neat handwriting from 1925 to 1929 is always the same and can surely be ascribed, based on several other existing samples, to Volta. From the end of 1929 onwards, we found more than one hand, and we cannot propose a sure identification for the others. The period well covered by existing notebooks is from 1925 to 1934. Afterwards, there are several gaps up to 1940, when Italy entered WWII. During the war period, there are only very sparse observations (for several months, the observatory site, being in an elevated position in the neighbourhoods of Turin, was taken over by a German army command post), not much more than a handful. The positions, at the beginning, were obtained rounded to 1 s of time in right ascension and 0' .1 in declination, but in a few years, they switched to the required standard of 0.1 s in RA and 1'' in Dec and communicated to the Central Bureau for Astronomical Telegram, at that time (and until 1965) hosted at the Copenhagen University Observatory. From time to time, regular lists containing both photographic and visual observations were sent for publication to some astronomical journals, mainly Astronomische Nachrichten and sometimes Journal des Observateurs.

New Minor Planets Apparently, no special program intended for discovering new objects was undertaken by Volta; however, either positively searched for or serendipitously found on plates aimed at “normal” programs for asteroid studies, a handful of new minor planets were caught as prey in the game bag of our observers. The first came out on the night of Dec. 13, 1928, and some excitement seems to have shaken director Volta and his staff;

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in fact, after a kind of a regretting note on the notebook reporting the observations of the night of November 18, where the position of 1928 WA is done, stating “.. (nuovo)?.. ma scoperto anche a Nizza la notte precedente” (new?.. but discovered also at Nice yesterday night) (ASOAT), we found, after the provisional name 1928 XC, the words, in red ink: (nuovo)–scoperto a Pino–(I osservazione) (ibid.) On the same plate, several other objects were measured as well, including 77 Friggia, 303 Josephina, and 477 Italia. (Fig. 7.7) After less than four months, a second catch occurred: on one plate taken on the night of March 30, 1929, another previously unknown solar system pilgrim left his trail, this time with only two companions: 386 Siegena and 438 Zeuxo. The notebook page marking the discovery tough still bearing some highlight compared to the normal sequence is not as flashing as the one dedicated to the first discovery: our hunters were getting acquainted with their prey. The third minor planet discovery came out on Feb. 11, 1931, and the dedicated notebook page looks now pretty normal: everyday life took over. The full list of discoveries that occurred in this first period of operation of the new Zeiss astrograph is reported in Table 7.2. According to the IAU rules for new object naming, in the case of a new minor planet, the discovery is assigned to the astronomer whose observations allow the computation of an orbit; he also has the right to propose a definitive name once the body has received the final numbering. Since these discoveries were all assigned, according to the MPC database, to Volta, we must assume that the final names listed in Table II had been proposed by him. Some kind of compliance and even flattery might be expected from a civil servant who is in charge of a scientific institution toward the central government personalities that hold the decisional power about money distribution, and indeed, we have here some clear clue of that. The first minor planet discovered was named after the royal house of the Italian king Vittorio Emanuele III, i.e., the house of Savoy, and two more names celebrated the emblem of the party and the person who was in charge of power in that period: the fascist party and his head (and then dictator) Benito Mussolini. Only for the last one, 1332 Marconia, was a different approach adopted, as it was not dedicated to a political association or figure but to one of the greatest Italian scientists of the twentieth century: Guglielmo Marconi. Another remarkable exception is 1191 Alfaterna, but we positively know that Volta left this asteroid unnamed. The proposal for its name was made in 1957 (accordingly to Min. Plan. Circ. N. 2882) by Alfonso Fresa: the name “Alfaterna” is after “Nuceria Alfaterna”, the Latin name of an old town founded approximately 1000 BC by the historic people of “Oschi” and located between Pompei and Salerno. It is now almost completely buried under the present town of Nocera Superiore that was, not by chance, Fresa’s home town.

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Fig. 7.7 Notebook page reporting the computation results of the position of the first minor planet discovered at Pino Torinese (INAF–Osservatorio Astrofisico di Torino, box 46, folder I, notebook n. 3) Table 7.2 Minor planets discovered at Turin Observatory by Luigi Volta

Final name

Discovery date

Provisional name

1107 Lictoria

March 30, 1929

1929 FB

1115 Sabauda

December 13, 1928

1928 XC

1191 Alfaterna

February 11, 1931

1931 CA

1238 Predappia

February 4, 1932

1932 CA

1332 Marconia

January 9, 1934

1934 AA

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After WWII, Some Changes Occurred The first period of systematic photographic and visual determination of minor planet and comet positions came to an end shortly after WWII. In the archive of Turin Observatory, approximately 620 photographic plates taken with the Zeiss astrograph from 1925 to 1942 are stored, most of them reproducing Solar System objects and a few tens with different targets, as a sort of occasional experiment. The war put much strain on astronomy personnel, mainly after the armistice of September 8, 1943, when the German occupation of most of the Italian territory was in place. The continuation of the scientific activity was very difficult or impossible at all due to the war condition, which implied the shortage of almost all provisions, both scientific and for everyday life. Moreover, in 1942, Volta asked for the transfer to Brera Observatory in Milan, and Gino Cecchini was appointed as his successor. He was already well acquainted with the problem of polar motion and latitude variations: after his graduation, his first employment as a young astronomer, from 1920 to 1927, was the assistant position first and then acting director at Carloforte, the Italian station of the International Latitude Service network. Of course, as soon as he arrived in Pino Torinese, he took care of all observatory activities, spending much effort to reactivate it to its full functionality after the war, although his main interest was in the aforesaid field. The central office of the ILS was in that period hosted at the Capodimonte Observatory in Naples, but his head, Luigi Carrera, was struggling with many difficulties. A general agreement was then reached between the Italian astronomers and the international committee managing the service to move the ILS central office from Capodimonte to Pino Torinese starting from January 1, 1949. Cecchini took charge of this hard and strenuous task until 1962, when the service was renamed International Polar Motion Service (IPMS) and the central office moved from Pino Torinese to Mizusawa in Japan. He did not spare any effort to improve the service, upgrading the observational program and discussing again all the previous observations to reach the greatest possible homogeneity of the results. During his directorship, however, almost all the existing instruments (except for the obsolete Reichenbach meridian circle, which was placed in a museum) were upgraded and provided with new observational devices (for instance, a photoelectric photometer was applied to the Merz refractor), but no new acquisition was performed. The tradition of observing and studying minor planets was at any rate well established and it was not lost, although almost interrupted after 1953: it enjoyed a remarkable resurgence with Cecchini’s successor, Mario G. Fracastoro.

Big Restart: New Telescopes and Astronomers In 1966, when Fracastoro took over the direction of the Turin Observatory, the research carried out at this institute was entirely related to the field of fundamental astronomy and astrometry. His scientific background, on the contrary, was much

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more based on astrophysics. Fracastoro made a bold decision challenging himself: do not change the observatory tradition but improve and enlarge the astrometric studies that were more oriented to the production of fundamental parameters such as stellar masses and distances. Solar system objects were not to be neglected, of course, but the well-established tradition in this field underwent modernization. The first step was to update and enlarge the observational arsenal: the small Zeiss astrograph was still good for observing bright minor planets, but although equipped with new objective lenses of much better performance, it was absolutely inadequate to obtain accurate stellar positions. (Fig. 7.8) A new reflecting telescope of 1-m diameter was thus ordered at the REOSC company in Paris. The chosen optical scheme was the so-called “astrometric”, such as the one that had been recently installed at the Flagstaff station of the US Naval Observatory (Strand, 1971). Due to a long-focus parabolic primary and a flat secondary mirror, it was optimized for obtaining very accurate star positions. The actual aperture of the finished telescope was 1050 mm with a focal length of 9942 mm. Completed in 1973 and covered by a new dome 10 m in diameter, it was intended for a program of photographic stellar parallaxes and double star measurements. At the same time, it was decided to acquire a second new astrometric telescope: a photographic refractor with a 380 mm aperture and 6875 mm focal length. The construction of the objective lens was commissioned to the Italian company Officine Galileo, whereas its design was committed to the wellknown optical engineer Cesare Morais (Boggio et al., 1972). This telescope was to be installed on a new mounting under the dome of the old 30-cm Merz refractor, which was retained and assembled in parallel as a guiding telescope. The new refractor provided good image performance over a larger field than the astrometric reflector: it could be used with plates of 20 × 20 cm, filling a gap between the Zeiss astrograph and the astrometric reflector. Moreover, another telescope was planned for photometric observations: a 450-mm aperture Cassegrain from the Italian optician Marcon, to be installed in an already existing dome. However, the telescopes, albeit new and powerful, were not enough: to do a good job you need a team of scientists, possibly young and industrious, who operate them. Consequently, the next step was to hire the astronomers. Indeed, providing the staff was even more difficult than providing the instruments, but thanks to both the teaching abilities of the new director and the lucky occurrence that the central government endorsed a substantial increase in observatory staff, it could be quite well fulfilled. The greatly enhanced human and instrumental provision soon sped up a blooming of results. From 1969 onwards, the rate of production of accurate minor planets’ positions markedly increased. Moreover, several collaborations with groups working in the same field in different institutions, both in Italy and abroad, were established. As a result, the Turin astronomers and technicians had the opportunity to conduct observational campaigns with telescopes located at sites better located than Pino Torinese, whose sky conditions were steadily deteriorating due to the massive development of the nearby city of Turin in the 1960s and 1970s. In 1982, an even more remarkable step (though, thanks to the aforesaid collaborations, some opportunities were also previously available) was the Italian membership in ESO, the European Southern Observatory, which brought the possibility of systematic observations of the southern sky from an outstanding

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location. The availability of more powerful telescopes yields a significant increase in the counting of new minor planets ascribed to Turin astronomers, up to approximately 40, all done with plates taken outside their home observatory. However, all the observational material was processed at home from plate inspection, measurement and computation of final positions. At the same time, a new branch of minor planets’ investigation was carried on, and in this field, some Turin astronomers became internationally acknowledged authorities: the photometric study of light variation. The combination of accurate light curves–obtained by photoelectric photometry - and spectroscopic data allowed the foundation of the physical study of these bodies, which were no longer considered just point-like masses for which to compute an orbit around the Sun. Fig. 7.8 The 1-m astrometric reflector used to observe faint minor planets and comets (author’s personal archive)

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The Last One For the Halley comet’s return, expected in 1986, a worldwide observational campaign, named International Halley Watch, was planned with the aim of organizing, collecting and analysing all kinds of data. The Turin Observatory was eager to participate, contributing both in astrometry (to improve the orbit’s determination) and photometry. The astrometric task was taken over by the author of this chapter, which at that time introduced and tested some new procedures for the measurement and reduction of photographic plates. Since the more extended in time the observed orbital arc of the body is, the more accurate the orbital parameters are, several observatories tried to obtain comet images well in advance of the perihelion passage. With this in mind, we were using the 1-m astrometric telescope, the most powerful available in our observatory, to take long-exposure images of the sky region overlapping the comet’s trajectory as dictated by its ephemeris. The comet was still too faint for our means: a long-focus telescope does not have a convenient optical layout for that purpose; however, by inspecting a plate taken on the night of December 28, 1983, a faint trail was seen. Better than nothing, it was undoubtedly a minor planet: the trail’s position was measured, and the information was sent to the MCP. We soon got the answer that no known asteroid matched those coordinates: this strongly suggested that it was a new one. We tried to gather additional observations to secure at least very preliminary orbital data, as asteroids observed only once are very likely lost. Due to the faintness of the object (just above the limit of our telescope) and the unfavorable sky conditions, we succeeded only on the nights of January 10 and 11. Anyway, this was enough to assign the discovery to us, with the provisional name 1983 YK for the new object. Not a very special one indeed, just a common main belt specimen. After a few years, enough observations have been collected (by others), and the final numbering assigned is 30768. This is the last minor planet discovered by the telescopes of Turin Observatory, and it is still waiting for a name.

References Beccaria GB (1774) Gradus Taurinensis. Turin, ex Typographia Regia. Bemporad G (1935) Sulla deduzione di posizioni fotografiche per mezzo di stelle di riferimento in numero sovrabbondante. Mem. SAIt, 8, 335–350. Boccardi, G. (1930) “Memorie della Mia Vita”, manuscript preserved at the Historical Archive of the Congregation of the Mission (Lazarists) in Turin (partial transcription provided by Amilcare De Leo and Marina Orio) Boggio, M., Fracastoro, M. G., Francese, G., Morais, C. (1972). Il rifrattore fotografico dell’Osservatorio Astronomico di Torino. Atti Fondazione Giorgio Ronchi, XXVII, 179–196. Cacciatore, G., Schiaparelli, G. V. (Eds.) (1874). Corrispondenza astronomica fra Giuseppe Piazzi e Barnaba Oriani. Publ. Oss. Astron. Di Brera n. 6. Carlini, F., & Plana, G. (1825). Opérations Géodésiques et Astronomiques pour la mesure d’un arc du parallèle moyen. Tome I. Carlini, F., & Plana, G. (1827). Opérations Géodésiques et Astronomiques pour la mesure d’un arc du parallèle moyen. Tome II.

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Schlesinger, F. (1911). Photographic determinations of stellar parallax made with the Yerkes refractor II. Astrophysical Journal, 33, 8–27. Schlesinger, F. (1926). A short method for deriving positions of asteroids, comets, etc., from photographs. Astrophysical Journal, 37, 77–84. Courir A. (ed.) (2009) Observing the Stars, 250 Years of Astronomy in Turin, Silvana Editoriale. Strand, K., Aa. (1971). The 61-inch astrometric reflector system. Publ. US Naval Obs., vol. XX Part I. Volta, L. (1933). Sulla deduzione delle posizioni fotografiche per mezzo di tre stelle di riferimento. Memorie della Società Astronomia Italiana, 7, 169–178.

Chapter 8

From the Biela’s Comet to Pluto’s Orbit: The Paduan Contributions Simone Zaggia and Valeria Zanini

Abstract Padua Astronomical Observatory had a long tradition in the calculation of orbital elements; ephemerides calculated by Giovanni Santini were by far considered the most reliable in the nineteenth century, including the contribution to the computation of Pluto’s orbit from Giovanni Silva and his staff in the 1930s.

The Astronomical Observatory of Padua: A Long Tradition in Mathematical Astronomy The Astronomical Observatory of Padua had a long tradition in the calculation of planetary orbital elements. This fame was acquired in the mid-nineteenth century, thanks to the third director of the Specola, Giovanni Santini (1787–1877). Santini was born in Caprese Michelangelo, in the province of Arezzo, Tuscany, and he was the third of eleven brothers. He studied law and attended free courses in mathematics and physics at the University of Pisa, but he did not graduate. The mathematical skills of the young student were particularly appreciated by the Tuscan statesman Vittorio Fossombroni (1754–1844) so much that in 1805, he patronaged his coming to the Astronomical Observatory of Brera in Milan. This study trip was a considerable economic effort for his family but allowed Santini to train himself in astronomical practice and to probe his mathematical skills with the guidance of Barnaba Oriani (1752–1832) and Francesco Carlini (1783–1862), among the best astronomers working at that time in Italy. Oriani was one of the most famous astronomers in Italy in that epoch (Tucci, 2013); he had provided an important contribution to the study of Uranus, discovered by William Herschel (1738–1822) on March 13, 1781, being among the first to

S. Zaggia · V. Zanini (B) INAF–Padua Astronomical Observatory, Padova PD, Italy e-mail: [email protected] S. Zaggia e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 I. Chinnici (ed.), Italian Contributions to Planetary Astronomy, Historical & Cultural Astronomy, https://doi.org/10.1007/978-3-031-48389-9_8

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calculate the new planet’s orbit and publish its tables. Another significant astronomical result achieved by Oriani was the theory of the orbital perturbations exerted by Jupiter on other celestial bodies with significantly inclined orbits. He was stimulated in this research by Pierre-Simon de Laplace (1749–1827), whom he met in Paris, and by the discovery of 1 Ceres, the first minor planet, at the beginning of 1801. Oriani, together with Bode, was the first to directly receive the news via private communication from the discoverer Giuseppe Piazzi (1746–1826), and he also immediately tried to calculate the orbit of the new object. Carlini (Giacobbe, 1977), instead, was in charge of the Astronomical Ephemeris of Milan, which were among the best available astronomical almanacs of the time together with the Berliner Jahrbuch and the Nautical Almanac. Although just a few years older than Santini, Carlini was his teacher, but he also became a dear friend to him. Thanks to his mentors, in 1806, Santini was appointed assistant astronomer at the Astronomical Observatory of Padua,1 which was headed by Vincenzo Chiminello (1741–1815), whom he later succeeded. Santini was director of the Paduan Observatory for sixty years, from 1817 to his death in 1877, and his direction totally coincided with the period of Austrian domination of the Venetian territories2 : a long period of stability and continuous development for Padua University, during which the Observatory was enriched with new and modern instruments, increasing its national and international prestige. During his long life, Santini held numerous positions within Padua University: he was Rector in the academic years 1824–1825 and 1856–1857, acting dean of the Philosophical Faculty in 1845–1846, and provisional dean of the Mathematical Faculty from 1845 to 1872. However, he obtained the title of “Doctor of Philosophy” only in 1824 to comply with Austrian university regulations, which required holding a university degree to obtain the chair. He was also awarded an honorary degree in mathematics by Padua University on March 21, 1851, when he was 64 years old. During his scientific career, Santini was mainly interested in studies of positional astronomy and celestial mechanics. In the first field, he carried out the five Paduan Catalogues, also known as Santini’s Catalogues, which are based on 30 years of positional observations of approximately 10,000 stars, up to the 10th magnitude, made with the great meridian circle purchased from the Imperial-Royal Polytechnic Institute of Wien—the present-day Technische Universität Wien—in 1837 (Di Giacomo et al., 2023; Zanini & Zaggia, 2017). Concerning celestial mechanics, Santini specialized in the calculation of cometary orbits: his study on the comet of Biela (official designation 3D/Biela), a short-period comet whose orbit was subject to strong perturbations by Jupiter, became particularly famous. 1

At that time Padua and Milan were part of the Kingdom of Italy (1805–1814), a kingdom in Northern Italy in personal union with France under Napoleon I. 2 The so-called “Lombardo-Venetian Kingdom”, was a crown land of the Austrian Empire from 1815 to 1866. It was created after the Congress of Vienna in recognition of the Austrian House of Habsburg-Lorraine’s rights to the former Duchy of Milan and the former Republic of Venice. The kingdom was ruled by the emperor himself and lasted for 50 years until the territory of Venice was formally transferred from Austria to France, and then handed over to Italy on 19 October 1866. A formal plebiscite marked the Italian annexation of Venice on 21–22 October 1866.

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This comet was discovered by the Austrian military officer and amateur astronomer Wilhelm von Biela (1782–1856) on February 27, 1826 (Biela, 1826) and was recognized to have a possible period of 6.75 years, connecting it to two previous comet appearances in 1772 and 1805. Santini immediately calculated the preliminary orbit, also considering the perturbations caused by the major planets, confirming an orbital period between six and seven years. His results were crucial to find the wandering celestial body during its 1832 transit. John Frederick William Herschel (1792–1871), who was in close contact with the Paduan astronomer, requested Santini’s ephemeris to detect the comet with his powerful 20-feet reflector in September 1832 (Fig. 8.1). He “directed that instrument, with a newly–polished mirror, to a point of the heavens determined by taking a mean of the right ascensions and declinations, calculated by M. Santini from his own and from Damoiseau’s elements” (Herschel, 1832, p. 117). The Paduan astronomer reviewed, corrected, and improved his calculations for the following appearance, expected to be in 1839, but unfortunately, this return of Biela’s comet happened under unfavorable conditions. Indeed, the comet reached its nearest distance from the Sun when the Earth was very distant from the comet itself: they were separated by a distance of approximately the diameter of the Earth’s orbit, i.e., approximately 300 million km. In this condition, the comet was invisible even by the most powerful telescopes of the time. Despite the lack of observational data for 1839, which could have helped to improve the orbital parameters, the 1846 return of Biela’s comet was predicted by Santini with extraordinary accuracy, as confirmed by the international press: In 1843, Santini published the result of his computations, in which he not only predicted the day and hour at which the comet, in 1846, would reach its shortest distance from the sun but also gave a detailed account of its path among the fixed stars during the months of December 1845 and January, February, March, April, and part of May 1846, the interval of time during which the comet would remain visible from the earth. (Mitchel, 1846, p. 5).

Since the early days of the comet’s return, when it was visible with the most powerful refracting telescopes, it appeared to be in the exact places, among the fixed stars, which had been predicted by the Italian astronomer more than three years before its return. At the end of 1845, it was first observed by Johann Gottfried Galle (1812– 1910) from the Berlin Observatory on the evening of November 28, very near the place predicted by Santini, and it looked like an extremely faint nebula. A few days later, it was also observed by James Challis (1802–1882) in Cambridge, England, and by Francesco De Vico (1805–1848), director of the Collegio Romano Observatory in Rome: Santini had predicted the comet’s route among the fixed stars with astonishing accuracy, not just about the day predicted but even within a few hours of the exact time. The most surprising and spectacular event, however, was observed for the first time on the night of January 12, 1846, by Matthew Fontaine Maury (1806–1873), in charge of the U. S. Naval Observatory in Washington, and immediately after confirmed by all the most important astronomers of the time, from James Challis to John Herschel himself. Maury discovered that what had hitherto appeared as a single comet was actually composed of two distinct and separate celestial bodies, sweeping through space side by side, in the very track that Santini’s predictions had pointed out for Biela’s comet. (Fig. 8.2).

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Fig. 8.1 First page of the letter by John Herschel to Santini, in which the English astronomer thanks the Italian colleague for the ephemerides, that helped him to a very early observation of the Biela’s comet (Historical Archive of the Astronomical Observatory of Padua (HAAOPd), Fondo Santini, Correspondence, v. IV, Letter by Herschel, 1832)

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Fig. 8.2 The Biela’s comet, as observed in February 1846, soon after split into two pieces (Guillemin, 1875, p. 230)

In the subsequent passage of 1852, following the 1846 break-up, the two cometary fragments were first detected by Father Angelo Secchi (1818–1878) in Rome, and they were so distant that they appeared as two distinct objects, each with its own orbit. In 1859, astronomers waited in vain and searched for a long time, but the comet remained invisible; thus, astronomers thought the two components were immersed in the light of the sun. The international community was again expecting new ephemeris from Santini, who was now regarded as the best comet’s computer, to search for it again in the following passages: May the illustrious astronomer of Padua yet live to witness many returns of this comet, which he has followed with so much ability and success for more than thirty years, and with whose history his own name is so intimately associated (Hubbard, 1860, p. 112).

In the meantime, the comet had disintegrated into smaller splinters due to the gravitational attraction of the Sun. During the expected 1872 return, instead of the comet, astronomers observed one of the most beautiful and spectacular visions of shooting stars. During the night of November 27, starting from sunset for more than 6 hours all over Europe, the sky was filled with an incredible meteor shower, with more than a thousand meteors per hour. Among the many reports from different observers, Francesco Denza (1834–1894) from Brera counted 33,400 meters in 6 hours, a number far less than the real one since it was impossible to count them all. The coincidence between this event and the passage of the Earth on the descending node of the orbit of the Biela’s comet just a few hours before was recognized.

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The phenomenon of shooting stars and meteor showers was inexplicable until a few years earlier; the Milanese astronomer Virginio Schiaparelli (1835–1910) offered a first report on the evidence of a connection between meteors and comets in 1866 (Schiaparelli, 1866), and the 1872 event confirmed his hypothesis, proving that shooting stars were caused by contact with the Earth’s atmosphere, which ignites the cometary fragments released by the remains of Biela’s comet (Schiaparelli & Denza, 1872).

The Astronomical Observatory of Padua in the Twentieth Century The calculation of the Biela comet’s ephemeris accredited the Paduan school of Santini as one of the best in the world in the field of mathematical astronomy. This fame was confirmed in the following decades, as shown, for example, by the contribution of the Padua Observatory to the solar parallax determination campaign in 1900. In 1898, a new asteroid, 433 Eros, was discovered. It was the first near-Earth object available for the Astronomical Unit determination, and in 1900, the opposition of October 30 would have brought it very near the Earth. The Comité International Permanent pour l’Exécution Photographique de La Carte du Ciel (Permanent International Committee for Photographic Execution of Sky-map) established a special temporary Commission for coordinating micrometric, heliometric, and photographic observations from different places on Earth, intending to determine solar parallax, from which the Astronomical Unit is derived. Fifty-one astronomical observatories, including Padua, took part in the project with visual and photographic observations. Antonio Maria Antoniazzi (1872–1925), assistant astronomer in Padua, observed the new planet from October 1900 to February 1901. Even if Antoniazzi worked under unfavorable conditions–he used a small diameter telescope3 located a few meters high on the ground, close to a river, with a damp atmosphere lighted by the new electric street lamps–his 122 observations were part of the data selected for the parallax calculations by Arthur R. Hinks (1873–1945) at the Cambridge Observatory because they turned out to be of the same quality as the observations obtained with much more powerful telescopes (Pigatto & Zanini, 2002). In 1913, Antoniazzi was appointed Director of the Padua Observatory, but only two years later, the outbreak of the First World War stopped all scientific activity. At the end of the war, the Paduan Observatory had obsolete equipment, partly damaged, and without consistent funding for a quick restart. Furthermore, Antoniazzi died prematurely in 1925, leaving the Observatory without leadership until 1926, when 3

It was the so-called ‘Dembowski’ telescope, a ’second-hand’ used instrument. It belonged to the amateur astronomer Ercole Dembowski (1812–1881) and was acquired by the Paduan Observatory after his death. The objective-glass of this telescope, made by Merz in 1862, had 187-mm aperture and 3,200-mm focal length (Pigatto, 2014; Zanini, 2017).

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Giovanni Silva (1882–1957), born in Legnago, in the province of Verona, Veneto, was entrusted with the direction. After completing his secondary studies in Verona, Silva attended the mathematics faculty at Padua University, following the courses of Giuseppe Lorenzoni (1843– 1914), the fourth director of the Observatory (Zanini, 2015), and those of Antoniazzi, and graduated in 1904 under the supervision of the famous mathematician Tullio Levi Civita (1873–1941). From 1905 to 1908, he worked as an assistant to Giuseppe Ciscato (1860–1908) at the Astronomical Station of Carloforte in Sardinia, which was involved in the international latitude service for studying the variation in latitudes caused by polar motion. On his return to Padua, Silva became assistant at the Geodesy Cabinet, housed at the Astronomical Observatory and directed by the same Antoniazzi. After the untimely death of Antoniazzi, he was asked to replace him, thus abandoning the direction of the Turin Astronomical Observatory that he had assumed in 1922. The scientific career of Silva, due also to the scarce resources available at the Observatory, was focused on geodesy and gravimetry and on classical astronomy. In the first field, he carried out several gravimetric campaigns in Italy for the Italian Geodetic Commission and the National Research Council, of which he was a member. In the field of classical astronomy, he devoted himself mainly to the study of celestial mechanical problems, developing original and effective calculation methods that allowed him and his collaborators to be among the first to accurately determine the orbit of the new planet Pluto, a few weeks after the discovery announcement.

1930: “Discovered Another World in Heaven” On March 13, 1930, the day on which Percival Lowell would have turned 75 and just 149 years after the discovery of Uranus, astronomers from all over the world received, by telegraph, the announcement of the discovery—desired and coveted for over twenty years—of a new celestial object, belonging to the Solar System but more distant than Neptune from the Sun. Circular no. 255 of the Central Office of the International Astronomical Union read: OBSERVATOIRE DE COPENHAGUE - TRANSNEPTUNIAN PLANET? We received from Prof. Shapley the following telegram: “Lowell observatory telegraphs systematic search begun years ago supplementing Lowell’s investigations for transneptunian planet has revealed object which for seven weeks has in rate of motion and path consistently conformed to transneptunian body at approximate distance he assigned fifteenth magnitude position march twelve three hours G.M.T. was seven seconds of time west from delta geminorum agreeing with Lowell’s predicted longitude. Shapley.”4

Soon, the news was reported all over the front pages of major international newspapers, especially in the USA. Coconino Sun, the local newspaper in Flagstaff, the town 4

See: http://www.cbat.eps.harvard.edu/iauc/00200/00255.html

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Fig. 8.3 Front page of the American newspaper Chicago daily tribune announcing the discovery of the new planet

of Arizona that hosts the Lowell Observatory, was titled “Achievement of Century”. The Chicago Daily Tribune headlined in capital letters: “See another world in sky”; more soberly, the New York Times read: “Ninth planet discovered on edge of solar system” (Fig. 8.3). The first news leaked from academic circles and fed to the press suggested that the planet was much larger than Earth, or even than Jupiter, and located at 45 Astronomical Units (AU) from the Earth.5 Between the discovery of Uranus in 1781 and that of Neptune, made by Johann Gottfried Galle (1812–1910) in 1846, 65 years had passed. Astronomers had spent an additional 84 years trying to locate traces of the presence of another planet in the depths of the solar system. The existence of a ninth planet has been hypothesized since the discovery of the last gas giant: in the orbital motions of Neptune and Uranus, some irregularities could not be explained by their mutual attraction or by the gravitational pull acting on them by the more massive planet Jupiter. They were explainable only through the presence of a “dark” perturbator. The American astronomers William Henry Pickering (1858–1938) and Percival Lowell (1855–1916) were among the main and most aggressive “hunters” of the new unknown celestial object. Lowell became famous for enthusiastically supporting the artificial nature of the “channels” observed by Schiaparelli on Mars and attributing them to an alien civilization (Lowell, 1911). He devoted himself entirely to the 5

The Knickerbocker Press, Albany, New York, March 14, 1930, in: www.rarenewspapers.com

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study of the planets, his main scientific interest, leading him to even build a new astronomical observatory in Arizona (Lowell, 1894) in 1894, where he spent the last ten years of his life searching for the mysterious ninth planet, which he nicknamed Planet X. Lowell began a systematic sky survey based on his theoretical research that provided dynamic evidence for the existence of a planet beyond Neptune (Lowell, 1915). This proof consisted of the analytical study of the residuals between the places of Uranus, observed from 1709 to 1910, and the theoretical positions of planet X, calculated according to the theory developed by Urbain Le Verrier (1811–1877) in 1873 and its subsequent improvement made by Jean Baptiste A. Gaillot (1834–1921). The residuals obtained from Gaillot’s theory were all kept below 2.5'' except for the year 1752, which amounted to 4.45'' , and at first sight, the alternations of the sign ruled out the perturbative effect of an unknown planet. Lowell, however, assumed the existence of an external perturbing body placed around the heliocentric longitude of 84° or 263°, and by rigorously applying the least squares method, he deduced that the sum of the squares of the residuals would decrease by 71%. The former position, at 84°, gave the smallest remnants, but astronomers in northern latitudes systematically observed this area of the sky, finding no trace of new celestial bodies. On the other hand, the second position was extremely low on the horizon for the main European and North American Observatories’ latitudes, so it was hitherto largely overlooked by the astronomers of the northern hemisphere. It was, therefore, the ideal candidate to go and look for the unknown planet. Lowell’s calculation provided an eccentricity of approximately 0.2 and an inclination of the orbit on the ecliptic plane of approximately 10°, making the planet even more difficult to find. Lowell had inadequate equipment at his disposal and could not reach any results. His survey was taken up again much more effectively only a few years after Lowell’s passing by his collaborators and successors: Vesto Melvin Slipher (1875–1969), who became director of the Lowell Observatory after the death of its founder, Carl Otto Lampland (1873–1951), and Clyde Tombaugh (1906–1997). The new campaign that led to the discovery of Pluto was performed thanks to the successful commissioning in 1929 of the new “Lawrence Lowell”6 telescope, which was specially designed to continue the hunt for the hidden planet. The telescope design was an “astrograph” in which large photographic plates, size 14 × 17 inches (35 × 42.5 cm) covering a field of 12 × 15 degrees, were exposed in approximately one hour of exposure. The negatives were then analysed by using a Zeiss blink comparator.7 In this way, Tombaugh revealed the presence of the new object on the plates of January 21, 23, and 29, 1930. After February 19, the new celestial body was then regularly photographed by Lampland with a 42-inch reflector and visually observed by Slipher and his brother Earl Charles (1883–1964) through the large Clark refractor, which had belonged to 6

The telescope was named in honor of Abbott Lawrence Lowell, Percival’s younger brother, who became president of Harvard University, and had funded it. See: https://lowell.edu/history/the-plutotelescope/ 7 The blink comparator was a device for highlighting the differences between two photographs of the same sky area taken at different times. It allowed you to quickly switch from one image to another, ‘blinking’ between the two, so it was easier to spot objects that changed position.

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Lowell himself. Finally, its retrogradation was detected, thus ensuring its planetary nature. It was only at this point that the official news was issued (Slipher, 1930). The new object was soon named Pluto to satisfy the tradition of assigning mythological names to the wandering stars and in honor of Percival Lowell. Pluto, indeed, was the name of the Roman divinity who ruled the kingdom of the dead; at the same time, its acronym, PL, coincided precisely with the initials of the astronomer who had hypothesized its existence with greater conviction.

Two and a Half Days of Calcoletti (Little Calculations) In Padua, Giovanni Silva began to engage with the new celestial body in early April 1930. Given his training and the astronomical practice exercised in the early years of his scientific career, he was particularly inclined toward the mathematical treatment of geodetic, gravimetric, and astronomical problems. He was, therefore, immediately intrigued and fascinated by the difficulty in calculating the new object’s orbit, also considering the numerous doubts advanced after its identification as a new planet. The surprising faintness of Pluto compared to the predictions generated the suspicion that it could have been a distant comet instead of a planet. The first calculations of the orbit gave parabolic or hyperbolic solutions, contributing to the doubts. It was, therefore, a priority to determine the actual path of Pluto as soon as possible, starting from the available observations to confirm the theoretical predictions. Silva did not have adequate instruments to carry out the positional observations of the new object from Padua. Following the first announcement on March 13, he had to wait for public data released from properly equipped observatories, including the Astrophysical Observatory of Catania and the Astronomical Observatory of Merate (near Milan), before engaging with the complex calculations. As soon as 14 daily positions (between March 16 and April 1) were available, Silva calculated his first Pluto’s orbit, which immediately turned out to be one of the most accurate and reliable among those in circulation. He dealt with the problem starting on Monday, April 7th, 1930, and over “two and a half days of calculations that I had put on last Monday for simple amateurism”,8 he immediately came to a positive solution, as he wrote two days later to his friend and colleague Emilio Bianchi (1875–1941), director of the Astronomical Observatory of Brera (in Milan). It is interesting to see how Silva came to this solution. First, he reported the observations available to him on graph paper, appropriately interpolating them at intervals of four equidistant dates: March 17.0, 22.0, 27.0 and 32.0 (Fig. 8.4). He immediately noticed that the classical methods of Gauss or Laplace, which allow obtaining all six parameters of a planetary orbit from just three observations using a highly complex mathematical apparatus, were of little applicability in this case. 8

“Due giorni e mezzo di calcoletti ai quali m’ero messo lunedì scorso per semplice dilettantismo” (Historical Archive of the Astronomical Observatory of Padua (HAAOPd), Fondo Silva, Correspondence, b. 1, Draft by G. Silva to E. Bianchi, April 14, 1930).

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Fig. 8.4 The first interpolations of Pluto’s observational data, performed on graph paper by Silva on April 7, 1930

The computational difficulties were given by the very short stretch of orbit travelled by the object (approximately 15 days on an orbit of 248 years, namely, less than 0.0166%!), and by its high orbital inclination with respect to the ecliptic. These two conditions led those who used the classical method to find the wrong solutions, parabolic or hyperbolic, as it was for Ernest Clare Bower (1890–1964) and Fred Lawrence Whipple (1906–2004) from Berkeley University. In their paper, they wrote: “These results clearly indicate that a distinctly trans-Neptunian orbit satisfies the positions thus far received. On the other hand, it is striking that the observations are satisfied by parabolas and that other differential corrections tend toward a high eccentricity” (Bower & Whipple, 1930, p. 190). At the end of the same month, Pickering still claimed: “I feel as if there could now be no doubt, based in part also on my own computations of possible planetary orbits, but that this object is simply a comet” (Pickering, 1930, p. 341). Silva, being a skilled mathematician, changed his approach to the problem in a rationally simple way, using the observational peculiarities of Pluto. He assumed that in the short observational period, the planet’s motion had been rectilinear and uniform, according to the tangent of the orbit, and therefore imposed that the three orbit segments, travelled in equal time intervals, had the same size. Thanks to a simple analytical development, he was, therefore, able to immediately derive the distance of Pluto, the inclination of the orbital plane, and the longitude of the heliocentric node. On April 9, Silva confirmed that the newly discovered celestial body corresponded just to the “object predicted by Lowell”. The next day, he immediately sent the communication of his calculations directly to Slipher in Flagstaff, to Hermann A. Kobold (1858–1942), director of the Astronomische Nachrichten, to Bengt G. D. Strömgren (1908–1987), director of the University Observatory of Copenhagen and seat of the “Central Bureau for Astronomical Telegrams”, and to Tadeusz Banachiewicz (1882–1954), director of the Krakow Observatory, a world eminence in the field of celestial mechanics and among the first to attempt calculations relating to the new object. Last but not least, Silva also sent his results to his friend Bianchi at Brera, asking him for a copy of Lowell’s Memoires, with the

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calculations of the predictions, since the Observatory of Padua did not have a copy because it was not on the Flagstaff mailing list.9 Once he read Lowell’s article, Silva could confirm that the first three orbital elements just calculated were in excellent agreement with the predictions of the American astronomer, indicating that his work process looked promising. Silva started calculating a second orbit in April using the radial velocity deduced from Lowell’s solutions. He presented his new results at the Galilean Academy of Padua and published them in early May in the Astronomische Nachrichten (Silva, 1930). His solution turned out to be the closest to the actual Pluto orbital elements ever published, while a near parabolic solution was still inexplicably obtained at the Lowell Observatory. It’s interesting to read Silva and Bianchi discussing why the Flagstaff Observatory had supported this wrong orbital solution so distant from Lowell’s solutions. Silva attempted to justify Americans for their use of classical methods, “by which you take the risk to achieve the eccentricity and the main axis from fractions very close to zero divided by zero, that is, the uncertainty”.10 On the other hand, Bianchi abruptly argued that “the calculation itself had to tell how convoluted they were. It is always the urge to arrive first, even when it is impossible”11 (FIG. 8.5). In the same issue of the Astronomische Nachrichten in which Silva published his paper, Eugène Joseph Delporte (1882–1955) from the Uccle Observatory, Belgium, published a position of Pluto found on a plate taken in 1927. Given the concordance with the position of the Uccle plate, Silva, spurred once again by Bianchi,12 faced a third calculation with the help of his assistants Francesco Zagar (1900–1976) and Ettore Leonida Martin (1890–1966). Other Observatories around the world found Pluto in their archival photographic plates. In addition to Uccle, for example, there were findings from 1921 and 1927 plates at Yerkes and 1919 at Mount Wilson Observatories. The simplified approach to calculating the orbit, which had allowed Silva to obtain a solid result, could now easily be generalized to exploit both these findings and the new observations that started to be gradually published. At the end of May 1930, while Silva was busy with teaching duties, Zagar carried out the task entrusted to him by the director to generalize the procedure, also taking into account the perturbations of the various planets. In this case, the process was 9

Silva complained about this in the April 10 letter sent to V.M. Slipher, presenting his first research results (HAAOPd, Ancient Archive, b. XXXI, f. 2). 10 “Si corre il rischio di avere l’eccentricità e l’asse maggiore da frazioni molto prossime al valore zero diviso zero, che corrisponde all’indeterminazione” (HAAOPd, Fondo Silva, Correspondence, b. 1, Draft by G. Silva to E. Bianchi, May 11, 1930). 11 “Il calcolo stesso doveva dire loro quanto fossero cervellotici. È sempre la mania di voler arrivare primo, anche quando farlo è impossibile” (HAAOPd, Fondo Silva, Correspondence, b. 1, Letter by E. Bianchi to G. Silva, May 14, 1930). 12 Bianchi urged Silva with these words: “As for the orbital elements, it will be very interesting to know what results you will bring; we hope that a communiqué will come from Padua stating, as I have no doubt, that astronomy is a school there. I will be infinitely glad” (“Quanto agli elementi orbitali sarà molto interessante sapere i risultati ai quali arriverai; speriamo che da Padova venga un comunicato che affermi, come non ne dubito, [che] l’astronomia è scuola di costà. Ne sarò infinitamente lieto”; HAAOPd, Fondo Silva, Correspondence, b. 1, Letter by E. Bianchi to G. Silva, May 6, 1930).

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Fig. 8.5 First page of the letter by Emilio Bianchi to Silva, dated May 14, 1930 (HAAOPd, Fondo Silva, Correspondence, b. 1, Letter by E. Bianchi to Silva, 1930)

different from the usual one: Zagar demonstrated that the overall perturbative action of the Sun and the first six planets up to Saturn, towards Pluto, could be seen as concentrated in the center of gravity of the seven bodies, greatly simplifying the calculation; therefore, it was necessary to use the classical perturbative method only for Uranus and Neptune. Then, proceeding through the method of least squares

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by successive approximations, Zagar obtained a new solution in November 1930, which turned out to be exceptionally precise (Zagar, 1930): this was confirmed, a posteriori, by the comparison with a position of Pluto found on a 1914 Heidelberg plate, which coincided within 1 arcsec with the Zagar solution, while the difference was more than 10 arcsec with the orbital solution proposed at the same epoch by Mount Wilson astronomers Seth Barnes Nicholson (1891–1963) and Nicholas Ulrich Mayall (1906–1993) and published in 1931 in the Astrophysical Journal. The two American astronomers received Zagar’s paper, mentioning it in their footnotes, but they neglected to highlight the best outcome of the Italian colleague compared to their work (Nicholson & Mayall, 1931). At the end of 1930, the Paduan astronomers Silva and Zagar considered the task of demonstrating the coincidence of Pluto with the Lowell object fulfilled. It was time to disseminate the results to the astronomical community and the general audience. To this end, on January 1, 1931, Silva published the results of the tiring and exciting work on Pluto in the first issue of the new magazine Coelum as the main article and most important topic (Silva, 1931). Guido Horn D’Arturo (1879–1967), director of the Bologna Observatory and creator of this first Italian magazine for the dissemination of astronomical knowledge, apologized to Silva for not being able to include his work as an opening article after having asked for it with very much insistence. Horn unfortunately granted this honor to Filippo Angelitti (1856–1931), director of the Palermo Observatory, due to the delivery times priority of his much more tedious article on “Probable Dante’s chronology based on data relating to the life of Jesus Christ and the life of Adam”. Silva instead published a mathematically exhaustive compendium in the Reports of the Mathematical and Physical Seminary of Milan in 1931.

Pluto is Well Worth a New Observatory After 1932, once Pluto’s orbit had been definitively established from a mathematical point of view, the astronomers of the Padua Observatory did not deal with Pluto for a long time because they were unable to use modern instrumentation. The Observatory did not have any updated equipment for contributing even minimally to contemporary observational astronomy. Silva complained several times to his friend Bianchi in this respect and about the impossibility of performing astronomical observations due to a lack of competitive instrumentation. In the 1930s, the largest Paduan instrument was a very obsolete telescope, the so-called “Dembowski”, equipped with a modest 19 cm achromatic doublet.13 Silva, therefore, needed to contact by telegraph his colleagues at Catania Observatory, which was involved with the “Carte du Ciel” enterprise (Lamy, 2021), to obtain new observations of Pluto. In July 1930, when the Paduan calculations on Pluto were still in full swing, Silva wrote a memorandum to the competent Ministry, exposing the “serious deficiencies” 13

See note 3.

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of the Specola in Padua, and echoing the ancient request of his predecessors to equip the Paduan observatory with an instrument up to the times and the prestige of the institution he directed.14 However, it was necessary to wait until the end of 1932 and the election of the new rector of the University of Padua, Carlo Anti (1889–1961), so that Silva could finally count on a powerful ally able to help him to find the necessary resources for the realization of a modern Astrophysical Observatory. Less than ten years later, Silva and Anti were able to inaugurate, side by side, the 122 cm “Galileo” reflecting telescope on the plateau of Asiago (located on the mountains 100 km northwest of Padua, at 1000 m altitude), at the time one of the greatest Italian masterpieces built as a symbol of the fascist autarchy. The telescope worked excellently, especially from the 1950s onwards, when it was equipped with a powerful spectrograph and the observations were supported by a Schmidt telescope for the discovery and study of new objects, in particular supernovae and variable stars. The availability of a new updated and modern astrophysical facility finally shifted the scientific interests of the Paduan astronomers towards more astrophysical matters, abandoning positional astronomy and orbit calculations which had characterised the activities of the Paduan Observatory for more than a century. The “Galileo” telescopie is still functioning and in good working order today after many update services. However, the relationship between Pluto and Padua did not stop in 1930 but was revived a few decades later, just after the end of the Second World War, and in more recent years. Pluto was repeatedly observed during the first operational nights of the Asiago “Galileo” telescope, but only after the construction of the 67/92cm Schmidt telescope15 in 1967, Leonida Rosino (1915–1997) and Cesare Barbieri (1942-) established a systematic program of astrometric observations, then continued with the largest Italian telescope, the “Copernico” 1.82 m16 at Cima Ekar (Barbieri et al., 1972, 1975 and 1979). This long survey covered more than 10% of the planet’s orbit, confirming that the Paduan astronomers never lost their interest in Pluto.

14

HAAOPd, Astrophysical Observatory of Asiago, b.1, f. 6. In 1961 Leonido Rosino, director of both the Padua astronomical observatory and the Asiago astrophysical one, spent two months at the Lick Observatory, where he was favorably impressed by the work carried out with an astrograph of 50 cm for discovering and surveying galaxy clusters. Therefore, he decided to equip the Asiago Observatory with a large Schmidt-type telescope, one of the main instruments of its kind in Europe. Thanks to this instrument, Paduan astronomers started consistently searching supernovae and flare variables and developed new studies for the census of galaxy clusters, quasars, RR Lyra, and Wolf-Rayet. The Schmidt 92/67 telescope was inaugurated in 1967, in the bicentenary of the Astronomical Observatory of Padua occurrence, although the telescope had already started working and had taken over a thousand photographs in the sky. See: https://www.oapd.inaf.it/sede-di-asiago/telescopes-and-instrumentations/schmidt-6792. 16 The Copernico 1.82 m telescope and its instruments are managed by the INAF Astronomical Observatory of Padua, on top of Mount Ekar (Asiago). It is the largest optical telescope in Italy. Dedicated to Nicolas Copernicus, it has been in operation since 1973 for optical imaging, low to medium–high resolution spectroscopy, and polarimetry using two main instruments: AFOSC (Asiago Faint Objects Spectrograph and Camera) and Echelle spectrograph. See: https://www. oapd.inaf.it/sede-di-asiago/telescopes-and-instrumentations/copernico-182 cm-telescope. 15

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