A rich cluster of galaxies identified in the Abell Catalog of Rich Clusters of Galaxies, which was the first comprehensive catalogue of clusters of galaxies and, in its extended form, is still the largest. The Abell Catalog was first published in 1958 by the American astronomer George Abell (1927-1983), a graduate student at the time, and contained 2,712 clusters of galaxies north of declination -27° identified by Abell from his analysis of the Palomar Observatory Sky Survey photographs.