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Loading contentTwo catalogues compiled by George Abell. The 1958 catalogue of rich clusters of galaxies — later extended southward — became the standard reference for galaxy clusters, listing thousands of the densest concentrations in the Universe. Separately, Abell catalogued 86 large, faint planetary nebulae. Objects carry an 'Abell' number in both.
Facts on this topic will be cited from these primary and reference sources.
Official naming, definitions, constellation boundaries, and astronomical nomenclature.