Clusters 'n Clusters - Abell Richness

Abell Richness is named both for the astronomer George
Abell and for the richness of galaxies in galaxy clusters.

A scale has been developed to study galaxy clusters and is
called the "Abell Richness Classes". This is a scale of six
categories of richness into which clusters of galaxies are
classified, and is based upon the number of galaxies
observed in the cluster that are not more than 2 magnitudes
fainter than the third-brightest member.

The higher the class number, the richer the cluster...

http://tinyurl.com/otndc

http://en.wikipedia.org/wiki/George_Abell

happy days and...
starry starry nights!

--
Indelibly yours,
Paine
http://www.painellsworth.net
http://www.savethechildren.org