This book collects together a selection of the best papers presented at the Third International Bioastronomy Symposium held in 1990. The subject is bioastronomy, the search for life in the universe, andthe book is devided according to the five main stages of life as recognized by this new branch of science: cosmic organic, prebiotic, primitive biological, and advanced. Thereader will find here the most recent results obtained by top specialists from all over the world on hot topics such as the formation and discovery of planets, organic chemistry in meteorites and comets, prebiotic chemistry in the atmosphere of Titan, the search for primitive life in the permafrost of Mars, and, SETI itself, the search for extraterrestrial intelligence. Complemented by live discussions each presentation forms a review of the state-of-the-art treatment of a particular area and also looks toward those developments in bioastronomywhich will surely be realized in the next few years.

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."

"Halten Sie es flir moglich, daB es auf anderen Himmelskorpern Leben gibt?" ist eine der haufigsten Fragen, welche Laien dem Fach astronomen steUen. Es ist in der Tat aufregend, sich vorzusteUen, wie auf anderen Planeten Pflanzen und Tiere gedeihen, Lebewesen, die vielleicht noch in einem Stadium sind, das dem Leben auf un serem Planeten vor Millionen Jahren ahnelt oder dem unseren in seiner Entwicklung weit voraus ist. Die Literatur bemachtigte sich des Stoffes. Kontakt zwischen verschiedenen Zivilisationen un seres MilchstraBensystems ist eines der haufigsten Themen der Science Fiction-Literatur. Niemand weiB bis heute, wie sich das Leben auf der Erde gebildet hat, wie aus unbelebter Materie lebende ZeUen wurden. Obwohl es keinen Grund gibt anzunehmen, daB immer, wenn die Bedingungen so sind, wie sie in der Erdgeschichte waren, auch wirklich Leben entsteht, kann man sich dem folgenden Gedan kengang nicht verschlieBen: Wir leben auf einem Planeten, der von einem Stern, urn den er kreist, warm gehalten wird. Bei der Bildung der Sonne entstand eine sie umstromende Gas- und Staubscheibe, in der die Planetenkorper auskondensierten. In unserem MilchstraBensystem gibt es mehr als hundert Milliarden Sterne, bei vielen muB es ahnlich zugegangen sein. SoUte sich da nicht auch Leben gebildet haben? Neuerdings hat man Staubscheiben urn andere Sterne entdeckt, vermutlich entstehen auch in ihnen Planeten. Wenn sich urn jeden Stern in Scheiben Planeten bilden, dann ist es auch denkbar, daB dort Prozesse ablaufen, die den erdgeschichtlichen Vorgangen glei chen. Die chemischen Elemente, auf denen das Leben basiert, sind liberaU vorhanden."

The immensity of the cosmos, the richness of the Universe, the limits of space and time: these are the themes of Cosmic Odyssey, which takes the reader on imaginary journeys through the past, present and future of our universe.

The extragalactic universe, the immense world of a billion galaxies lying beyond out own, is the subject of this book. Our Sun is but a tiny star among a hundred billion other in our Galaxy, the Milky Way, which appears as a luminous veil trailing across the clear night sky. Beyond the Milky Way we will soar into space amid galaxies, clusters of galaxies, radio galaxies and quasars of enormous energy, out to the cosmological horizon which arrests our flight like an intangible barrier. Why do galaxies seem to fly from us? Is space so strongly curved that by going straight ahead we come up behind ourselves? Did it all begin with an enormous explosion, the famous Big Bang, which decided our fate in the first quarter of an hour? These are the questions which this rigourous and enthusiastic scientist tries to answer with complete honesty and non-technical clarity.