(A, ACO) A catalogue of 2712 rich clusters of galaxies produced by George Abell in 1958 from careful examination of the Palomar Sky Survey plates. It was extended in 1989 by George Abell, Harold Corwin and Ron Olowin to include an extra 1364 rich clusters in the far southern hemisphere not covered by the original Palomar Sky Survey. It contains most of the richest clusters of galaxies within 3 billion light years.

The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift z = 0.2. This catalog supplements a revision of George Ogden Abell’s original “Northern Survey” of 1958, which had only 2,712 clusters, with a further 1,361 clusters – the “Southern Survey” of 1989 – from those parts of the south celestial hemisphere that had been omitted from the earlier survey.