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 NGC 1912 (M38) depicted below is one of three well-recognized clusters in the constellation of Auriga all lying within a few degrees of each other (the other two being NGC 1960 (M36) and NGC 2099 (M37)). The cluster lies at the midpoint of the imaginary line joining ι- and θ-Aur and is the northernmost of these three clusters. The cluster is quite large and covers an area of approximately 21'x21' and with a diameter of approximately 25 light-years across. The distance to this intermediate aged cluster (220 million years old) has been estimated at around 4200 light-years. As indicated by the image below and in spite of its intermediate age, NGC 1912 is quite rich in young stars ranging from 8th to 10th magnitude.

The cluster was discovered by Giovanni Batista Hodierna in 1654 and independently rediscovered in 1749 by Le Gentil. Charles Messier catalogued the cluster in September, 1764 as the thirty-eighth entry in his catalog of deep sky oblects. The cluster lies in nearly a vertical line with the other two primary clusters in Auriga (M36 and M37) being the middle cluster of the set. All three clusters are best observed using low magnifications during fall and winter where they are placed directly overhead when looking due east.