rlier this April, NASA's Compton Gamma Ray Observatory, completed its fifth successful year in orbit, exploring the gamma ray sky. Pictured is astronaut Jay Apt perched in the shuttle payload bay below the massive observatory. Compton is the largest civilian instrument ever flown - the whole observatory is roughly the size of a school bus. Apt and colleague Jerry Ross rescued the spacecraft from an unexpected problem by successfully freeing the stuck high gain antenna in an unplanned space walk. The second of NASA's planned Great Observatories for Space Astrophysics, the first being the Hubble Space Telescope, the Compton Gamma Ray Observatory has exceeded expectations of scientific discovery. Compton continues to search the depths of the universe for such high energy phenomena as gamma-ray bursts, blazars, and pulsars. Compton is still monitoring a new source it discovered just last December - the spectacular "bursting pulsar" near the center of our Galaxy. Information: The Scale of the Universe Debate in April 1996