Open star clusters are widely distributed in our galaxy and represent a loose collection of stars which number from a few dozen to a few hundred stars and are weakly-held gravitationally. Perhaps the three most famous such open clusters are the Pleiades (M45) in Taurus, the Beehive (M44) in Cancer and the double cluster in Perseus. They are all characterized with a handful of hot and white prominent stars and nebular material surrounding these stars.

Note: Open cluster M26 depicted below is a bright but low-density cluster comprised of 70 member stars with a handful of mag 10 and predominantly mag 11.9+ stars. As illustrated by the image below, the cluster lies in the heart of the Milky Way and within the rich and dense Scutum cloud. The cluster spans 22 light-years across and lies at a distance of 5,200 light-years away while it has been dated to be relatively young at about 89 million years of age. A frequent observation made in relation to M26 is the fact the central portion of the cluster is relatively less dense than the rest of the cluster and which is believed to be due to intergalactic dust. M26 was discovered by Charles Messier on June 20th, 1764.