Complex sentence: Abell 2065 is a highly concentrated galaxy cluster containing more than 400 members, the brightest of which are 16th magnitude; the cluster is more than one billion light-years from Earth.
Split into simpler sentences: Abell 2065 is a highly concentrated galaxy cluster containing over 400 members, the brightest of which are 16th magnitude. The cluster is more than one billion light-years from Earth.