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: The open cluster NGC 663 illustrated below lies in a rich portion of the sky and which includes various other open clusters including M103 and NGC 457. The cluster is estimated to be 9 million years old and to contain the most Be stars of any open cluster. Comprised of over 100 bright member stars measuring at least 8.5 magnitude, this cluster is not only bright but is large and quite well detached from the background sky. NGC 663 is best observed during fall and winter when it is furthest north of the celestial pole after the end of astronomical twilight.