Quoted from SEDS:
Discovered by Giovanni Batista Hodierna before 1654.
Although Messier 37 (M37, NGC 2099) is the brightest of the 3 open
clusters in southern Auriga, this cluster was missed 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 before 1654.
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 years. Its distance is given
discordantly: Kenneth Glyn Jones gives 3,600 light years, the Sky
Catalog 2000 has 4,400 while Götz gives about 4,100, Mallas 4,600, and
Burnham 4,700 light years. Its apparent diameter of 24' corresponds to a
linear extension of about 20 to 25 light years, according to which
distance is taken. It was classified as of Trumpler type I,1,r or I,2,r. |