M 37

Although M37 is the brightest of the 3 open clusters in southern Auriga, this cluster was misseds by Le Gentil when he rediscovered M36 and M38 in 1749, so that it was to Charles Messier to find this one independently on September 2, 1764 (generally unknown until 1984, all three clusters had been previously recorded by Hodierna).

M37 is the also the richest of the 3, containing about 150 stars brighter than mag 12.5, and perhaps a total of over 500 stars. As indicated by the fact that it has a considerable number (at least a dozen) of red giants, and that the hottest main sequence star is of spectral type B9V, this cluster is a more evolved group with an estimated age of about 300 million light years. At its distance of 4,700 light years, its apparent angular diameter of 25' corresponds to a linear extension of about 25 light years.

Right ascension	05 : 49.0 (hours : minutes)
Declination	+32 : 33 (degrees : minutes)
Distance	4600.0 (light-years*10^3)
Visual magnitude	6.2