Leo Goldberg Kitt Peak National Observatory Tucson, Arizona 85726, U. S. A. Of all the reasons for exploring the Universe, none is more com­ pelling than the possibility of discovering intelligent life elsewhere in the Universe. Still the quest for extraterrestrial life has been near the bottom of the astronomers' list of priorities, not because the number of extraterrestrial civilizations is conjectured to be van­ ishingly small, but because our powers of detection were thought to be far too weak. About ten years ago, however, the growing reach of ra­ dio telescopes on the ground and of optical and infrared telescopes in space persuaded a number of thoughtful astronomers that the time for a more serious search had arrived. Accordingly, a joint Soviet-American conference on the problems of Communication with Extraterrestrial In­ telligence was convened at the Byurakan Astrophysical Observatory of the Armenian Academy of Sciences during September 5-11, 1971 and was soon followed by a number of other important meetings, notably a series of NASA-sponsored workshops in the USA held between January, 1975 and May, 1976. Since SETI is fundamentally an international undertaking and as­ tronomical methods and techniques are required for its pursuit, it is natural for the International Astronomical Union to lend its support by sponsoring conferences and otherwise facilitating cooperation among countries. The active involvement of the I. A. U.

Inhalt

Highlights.- Highlights of the Proceedings.- I. The Number N of Advanced Civilizations in Our Galaxy and the Question of Galactic Colonization.- N is Very Small.- N is Neither Very Small nor Very Large.- Galactic-Scale Civilization.- The Number N of Galactic Civilizations must be Either Very Large or Very Small.- Uncertainty in Estimates of the Number of Extraterrestrial Civilizations.- A New Approach to the Number N of Advanced Civilizations in the Galaxy.- II. Strategies for SETI Through Radio Waves.- Microwave Searches in the U.S.A. and Canada.- A Bimodal Search Strategy for SETI.- III. The Search for Planets and Early Life in Other Solar Systems.- The Astrometric Search for Neighboring Planetary Systems.- Search for Planets by Spectroscopic Methods.- The Search for Planets in Other Solar Systems Through Use of the Space Telescope.- A Comparison of Alternative Methods for Detecting Other Planetary Systems.- The Search for Early Forms of Life in Other Planetary Systems: Future Possibilities Afforded by Spectroscopic Techniques.- IV. Manifestations of Advanced Cosmic Civilizations.- Starships and their Detectability.- Radio Leakage and Eavesdropping.- Conclusions.- Conclusions and Recommendations from the Joint Session.