m37 ngc 2099 open cluster in auriga

Messier 37 (also known as M37 or NGC 2099) is the richest open cluster in the constellation Auriga. It was discovered by Hodirena before 1654.

Messier 37 is the brightest of the three open clusters in Auriga. M37 was missed by Le Gentil when he rediscovered M36 and M38 in 1749. Charles Messier independently rediscovered M37 in September of 1764 but all three clusters were recorded by Hodierna before 1654.

M37 is roughly 300 million years old and contains over 500 stars with roughly 150 stars brighter than magnitude 12.5. M37 also contains at least a dozen red giants with the hottest main sequence star of spectral type B9V. Its distance is between 3,600 to 4,700 light years and the apparent diameter of 24' corresponds to a linear extension of about 20 to 25 light years. It is classified as Trumpler type I,1,r or I,2,r.