At the center of this picture, is our Local group of galaxies. A group of galaxies is a small cluster. True clusters of galaxies have thousands of galaxies like the Milky Way. We will look a bit more closely at a few of the more notable clusters. The closest cluster of galaxies is the VIRGO cluster. The scale of this image to the right is several HUNDRED million light years in diameter.

The Virgo Cluster, is about 60 Mly away and contains >2000 galaxies! It is the closest MAJOR cluster. We (the Milky Way and Local Group) are currently falling into Virgo at a rate of several 100 km/s. Galaxies at the center move with velocities up to 1500 km/s, due to the central gravity. It's clear to see that within galaxy clusters, collisions routinely occur between galaxies.