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: As indicated by the image below, NGC 2168 (M35) lies in a rich field comprised of many stars. With an apparent diameter of 28 arc-minutes, just slightly less than that of the full moon, this cluster has been estimated to be approximately 100 million years of age and to span 24 million light-years in diameter. The cluster is comprised of several hundred member stars including over 100 stars with a magnitude of 13 or brighter and includes several post-main sequence yellow and orange giants which are also evident in the image below. The cluster is best observed during winter using low magnifications (50-100x) and is located a few degrees due east of the double-star system Propus (η-Gem, mag 3.35). Although independently discovered by both Philippe Loys de Cheseaux (1745-1746) and John Bevis (1750), Messier's inclusion was based on the reference and observation by Bevis whom he acknowledged as his source.