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...