THE COMPTON-GAMMA-RAY-OBSERVATORY

The Arthur Holly Compton Gamma Ray Observatory (Compton) is the second in NASA's series of Great Observatories. Launched on 1991 April 5, Co mpton represents a dramatic increase in capability over previous gamma -ray missions. The spacecraft and scientific instruments are all in go od health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of ea rly discoveries by Compton are enumerated, including the discovery tha t gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacti c gamma-ray sources, the gamma-ray AGNs; the discovery of emission fro m SN 1987A in the nuclear line of Co-57; and the mapping of emission f rom Al-26 in the ISM near the Galactic center. Future observations wil l include deep surveys of selected regions of the sky, long-term studi es of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for sm all anisotropies. After completion of the all-sky survey, a Guest Inve stigator program is in progress with guest observers' time share incre asing from 30% upward for the later mission phases.