ar X iv : 0 81 1 . 35 35 v 1 [ as tr o - ph ] 2 1 N ov 2 00 8 Galaxy systems in the optical and infrared

1 . 1. Identification. – Historical identifications of clusters of nebulæ date back to the late years of the XVIII century [1]. The first modern method of galaxy clusters identification and classification was implemented by Abell [2] in 1958. Abell worked out apparent overdensities of galaxies in the sky by eye inspection of photographic plates of the Palomar Observatory Sky Survey. He used the apparent magnitudes of galaxies to determine approximate cluster distances which he then used to convert apparent sizes to physical sizes. Abell characterized clusters by their richness, i.e. the number of galaxies in the 2 mag range m3 to m3 + 2( ) in a circle of radius 2.1 Mpc(), corrected for the