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 double cluster in Perseus comprised of the two constituent open clusters NGC 869 and NGC 884 is a spectacular sight through a low-power eyepiece. These clusters had been observed in antiquity based on the references by Hipparcus (130 BC). Both NGC 869 and 884 were first discovered by Pierre Mechain in 1781. The two member clusters are quite young in age (3.2 and 5.6 million years old) and are about 7,000 light-years away. The cluster is very easy to locate since it lies within a degree of δ-Cassiopeiae (Ruchbach, mag 2.65) and is best observed during late summer and early fall when it is directly overhead around midnight.

Note: The result below is a two-part mosaic involving NGC 869 and NGC 884.