An Etymological Dictionary of Astronomy and Astrophysics
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The property of being very abundant.

→ rich; → -ness.

A classification of → galaxy clusters into six groups (0 to 5), as in the → Abell catalog. It depends on the number of galaxies in a given cluster that lie within a → magnitude range m₃ to m₃₊₂, where m₃ is the magnitude of the 3rd brightest member of the cluster. The first group contains 30-49 galaxies and the last group more than 299 galaxies.

→ richness; → group.