Since the first French edition of the book emphasized rather the solid facts of Cosmology than the detailed discussions of controversial results, relatively few revisions were necessary for the English edition. They were made early in 1979 and affected about 5% of the text. The main revisions referred to the distance scale, the dlstribution of galaxies, the X-ray observations of clusters, the cosmic time evolution of quasars and radiogalaxies and the 3 K radiation. A new short bibliography presents the recent articles and the latest proceedings of Symposia; from these the reader can easily trace a more complete list of refer ences. I am happy to thank Professor Beiglbock for suggestions he made to improve Part lIon Spaces of Constant Curvature, and Drs. S. and J. Mitton for translating the manuscript into English. I also thank with pleasure Marie-Ange Sevin for correcting the final version. J. Heidmann March 1980, Meudon, France Preface The aim of this book is to present the fundamentals of cosmology. Its subject is the study of the universe on a grand scale: - on a grand distance scale, since from the start, we shall be escaping the con fines of our own Galaxy to explore space as far as the limits of the observable universe, some ten thousand million light years away; - and on a grand time scale, as we shall look back into the past to the very first moments of the initial expansion, about twelve thousand million years ago."

Symposium No. 73 of the International Astronomical Union was devoted to the obser vational and theoretical aspects of close binary stars. Just over 100 participants attended. The Local Organizing Committee would like to thank the following: IAU for travel grants. IBM United Kingdom Ltd for very generous support in the form of travel grants. The Royal Society for the provision of travel grants to participants from Eastern Europe. We also thank the Director of the Institute of Astronomy, and our colleagues and research students for their moral support and assistance. Finally we thank Pauline Haughey for assisting with the editorial work. PETER EGGLETON SIMON MITTON JOHN WHELAN SCIENTIFIC ORGANIZING COMMITTEE M. Plavec (Chairman), T. Herczeg, E. P. J. van den Heuvel, J. B. Hutchings, G. Larsson-Leander, L. B. Lucy, L. Mestel, B. Paczynski, J. Sahade, B. Warner, R. E. Wilson. LOCAL ORGANIZING COMMITTEE J. A. J. Whelan (Chairman), P. P. Eggleton, S. A. Mitton LIST OF PARTICIPANTS Baldwin, B. W., Victoria, Canada Icke, V., Cambridge, England Bateson, F. M., Tauranga, New Zealand Koumsiachvilli, M., Moscow, U.S.S.R Bath, G. T., Oxford, England Krzeminski, W. A., Warsaw, Poland Batten, A. H., Victoria, Canada Larsson-Leander, G., Lund, Sweden Berthier, E. J., Paris, France Leung, K.-C., Nebraska, U.S.A."

Symposium No. 73 of the International Astronomical Union was devoted to the obser vational and theoretical aspects of close binary stars. Just over 100 participants attended. The Local Organizing Committee would like to thank the following: IAU for travel grants. IBM United Kingdom Ltd for very generous support in the form of travel grants. The Royal Society for the provision of travel grants to participants from Eastern Europe. We also thank the Director of the Institute of Astronomy, and our colleagues and research students for their moral support and assistance. Finally we thank Pauline Haughey for assisting with the editorial work. PETER EGGLETON SIMON MITTON JOHN WHELAN SCIENTIFIC ORGANIZING COMMITTEE M. Plavec (Chairman), T. Herczeg, E. P. J. van den Heuvel, J. B. Hutchings, G. Larsson-Leander, L. B. Lucy, L. Mestel, B. Paczynski, J. Sahade, B. Warner, R. E. Wilson. LOCAL ORGANIZING COMMITTEE J. A. J. Whelan (Chairman), P. P. Eggleton, S. A. Mitton LIST OF PARTICIPANTS Baldwin, B. W., Victoria, Canada Icke, V., Cambridge, England Bateson, F. M., Tauranga, New Zealand Koumsiachvilli, M., Moscow, U.S.S.R Bath, G. T., Oxford, England Krzeminski, W. A., Warsaw, Poland Batten, A. H., Victoria, Canada Larsson-Leander, G., Lund, Sweden Berthier, E. J., Paris, France Leung, K.-C., Nebraska, U.S.A."

Die Erforschung des Universums muss als eine der grossen intellektuellen Leistungen unserer Zivilisation betrachtet werden. Astronomen koennen uns heute mittels grosser, empfindlicher Teleskope in eine fruhe Epoche in der Entwicklung des Universums zu- ruckversetzen. Unser Wissen von den Massen des Kosmos und von seinen Ursprungen stammt groesstenteils von Beobachtungen von Objekten jenseits der Milchstrasse. Zu diesen Himmelskoerpern gehoeren Quasare, Radiogalaxien und aktive Galaxien genauso tlie die normalen Spiral- und elliptischen Galaxien. Unser Verstandnis vom extraga- Universum ist stark gewachsen, seitdem Radio-, Infrarot- und Roentgenmes- laktischen sungen ziemlich leicht gemacht werden koennen. Die Erschliessung dieser unsichtbaren Teile des Spektrums fuhrte zu einem explosionsartigen Anwachsen der Forschungstatig- keit an extragalaktischen Objekten. In diesem Buch habe ich versucht, in nichttechnischer Sprache die grundlegenden Eigenschaften von Galaxien und die Hauptstroemungen gegenwartiger Forschung zu er- lautern. Die zweite Halfte des Buches befasst sich mit einer Darstellung der haupt- sachlichen Probleme extragalaktischer Forschung, denen sich der Berufsastronom ge- genubergestellt sieht. Viele Kollegen unterstutzten mich, als ich dieses Buch schrieb. Im besonderen danke ich Donald Lynden-Bell, Jacqueline Mitton, Patrick Moore, Martin Rees, John Shakeshaft und Peter Stubbs fur ihr Interesse und ihren Ansporn, sowie den vielen Leuten, die Illustrationen bereitstellten. Eine ungeheure Menge an Schreibarbeit wurde fachkundig von Gertrude Pardoe bewaltigt. Institute of Astronomy, Cambridge, England Simon Mitton im Mai 1975 Vorwort der UEbersetzer Die deutsche Fassung dieses Buches stellt eine wortgetreue ubersetzung des englischen Originaltextes dar. Lediglich in Detailfragen wurde sie uberarbeitet oder korrigiert, insbesondere wenn neuere Ergebnisse der Forschung dies notwendig erscheinen liessen.