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 6939 in Cepheus is weakly detached from the background sky and as indicated by the image below. It is comprised of approximately 150 stars mostly between 12th and 13th magnitude in a triangular formation and covering an area of approximately seven arc-minutes while lying less than 0.7° away from the Fireworks Galaxy (NGC 6946). NGC 6939 has been estimated to lie 3,865 light-years away and to be intermediate-aged at about 2.21 billion years old. The cluster is best observed using midpower magnifications (100-200x) during late fall and winter. NGC 6939 was discovered by William Herschel in 1798.