The Coma Cluster is the nearest massive cluster of galaxies, also known as Abell 1656; it is roughly spherical, about 20 million light-years in diameter, contains more than 3,000 galaxies, and lies about 280 million light-years away in the constellation Coma Berenices. Its location close to the north galactic pole makes it ideally placed for observation free from the effects of galactic obscuration.
As is usual for clusters of this richness, the largest member galaxies are overwhelmingly elliptical or lenticular, with only a few spirals (most of these probably near the outskirts of the cluster). The central region is dominated by two giant galaxies: NGC 4889 (an elliptical) and NGC 4874 (an S0 type). The Coma Cluster contains hot intra-cluster gas that is an extended source of X-rays, about 0.5° across, known as Coma X-1.