Table of contents : Preface Acknowledgments Contents 1 Youth in Oegstgeest and Leiden 1.1 Franeker 1.2 Oegstgeest 1.3 `Hoogere Burgerschool' in Leiden 2 Kapteyn and Galactic Astronomy Around 1920 2.1 Jacobus Cornelius Kapteyn 2.2 The Kapteyn System 3 Student at the University of Groningen 3.1 Student Life in Groningen 3.2 Kapteyn's Lectures 3.3 Astronomical Research 4 Via Yale to Leiden 4.1 Leiden Observatory (Sterrewacht Leiden) 4.2 The IAU in Rome 4.3 To America 4.4 Yale Observatory 4.5 Life in New Haven 4.6 To Leiden 5 Rotation and Dynamics of the Milky Way Galaxy 5.1 Absolute Declinations 5.2 PhD in Groningen 5.3 Johanna Maria Graadt van Roggen 5.4 The Rotation of the Galaxy 5.5 Harvard, Columbia or Leiden? 6 The Structure of Our and Other Galaxies 6.1 The Oort Limit 6.2 Perkins Observatory 6.3 The Succession of de Sitter 6.4 An Expedition to Kenya 6.5 General Secretary of the IAU 6.6 Absorption and the Structure of the Galaxy 6.7 The McDonald Inauguration 6.8 Mount Wilson 7 The Watershed: World War II 7.1 First Years of the War 7.2 Personal Matters and Scientific Research up to 1942 7.3 Nova Persei 1901 and the Crab Nebula 7.4 Astronomers Conferences 7.5 The Potbrummel at Hulshorst 7.6 Interstellar Medium 8 Breaking New Ground 8.1 Director of Sterrewacht Leiden 8.2 Recovery of the IAU 8.3 The Interstellar Medium 8.4 Yerkes, McDonald and Palomar 8.5 Kenya and South-Africa 8.6 The Oort Cloud 8.7 The Oort Family 9 From Kootwijk to Dwingeloo 9.1 The Discovery of the 21-cm Line 9.2 Spiral Structure of the Galaxy 9.3 Pasadena, Princeton and Gas Clouds 9.4 Back to the Crab 9.5 President of the IAU 9.6 The Dwingeloo Radio Telescope 10 The Structure of Our Galaxy and Dwingeloo 10.1 Administrative Work 10.2 Stellar Populations at the Vatican 10.3 South-Africa and Chile 10.4 More Dynamics 10.5 Research in Dwingeloo 11 Westerbork and Retirement 11.1 Personal Matters 11.2 Honors, Golden Quill and Vetlesen Prize 11.3 The Westerbork Synthesis Radio Telescope 11.4 Retirement 11.5 Westerbork and Nearby Galaxies 11.6 More Astronomical Research 11.7 Pocket Diaries and End-of-Year Highlights 12 The Last Horizon 12.1 Superclusters 12.2 Return of Halley 12.3 Balzan and Kyoto Prizes 12.4 Personal Matters 12.5 The End A Astronomical Background A.1 Kepler and the Orbit of Mars A.2 Positional Astronomy A.3 Properties of Stars A.4 Stellar Evolution B Honors and Genealogy B.1 Awards, Prizes and Honorary Doctorates B.2 Academic Genealogy C Literature References Index