Regular Clusters
Regular clusters are spherically symmetric, with the galaxies concentrated toward the center of the cluster. They usually contain at least 1,000 galaxies which are brighter than an absolute magnitude of -16.
Regular Cluster - A cluster of galaxies that has roughly spherical symmetry
Regular Satellites - Regularly spaced satellites with nearly circular orbits that form miniature "solar systems" about their parent planets ...
An irregular cluster of about 2500 galaxies (z = 0.004), including the giant elliptical M87 (the galaxy of greatest known mass).
Virgo Infall ...
A diffuse, irregular cluster of about 500 galaxies (z = 0.0183) (richness class 2) dominated by and centered on the Seyfert galaxy NGC 1275 (Perseus A). Mass required to bind the cluster, greater than 1015 M; mass of cluster, about 2 × 1015 M. [H76] ...
It is a poor, irregular cluster with some 20 certain members including the Milky Way Galaxy, the Andromeda Galaxy, the Triangulum, four irregular galaxies, and about 13 intermediate or dwarf ellipticals.
Regular clusters are huge spherical groupings of galaxies with large numbers of galaxies concentrated in their centers. They tend to contain thousands of galaxies and to have many bright elliptical and S0 type galaxies.
Irregular Galaxy Cluster: Clusters of galaxies that are not too centrally condensed, with a somewhat nonspherical overall shape, containing a few galaxies up to hundreds of galaxies. Our local group is an example of an irregular cluster of galaxies.
Coma (about 5 times the Virgo distance) is the nearest rich, regular cluster and a useful standard of comparison.
 See also: Universe, Galaxy, Galaxies, Cluster, Mass
  
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