Degree of difficulty 2 (of 5)

Minimum aperture Naked eye

Designation NGC 2099

Type Open cluster

Class I2r

Distance 4510 ly (K2005) 6720 ly (2004) 4510 ly (proper motion, 2002) 6660 ly (CMD, 2001)

Size 33 ly

Constellation Auriga

R.A. 5h 52,5min

Decl. +32° 33′

Magnitude 5.6

Surface brightness –

Apparent diameter 25′

Discoverer Hodierna, 1654

History M 37 was discovered before 1654 by Giovanni Batista Hodierna, who saw a “nebulous patch.” Unaware of Hodierna's observation, Messier made an independent discovery of M 37 on the 2nd of September 1764, and described a “cluster of faint stars, at little distance from the previous [M 36]; the stars are very faint, close, and contain some nebulosity.”

Around 1830, Smyth noted enthusiastically: “The whole field being strewed as it were with sparkling gold-dust; and the group is resolvable into about 500 stars, from the 10th to the 14th magnitudes, besides the outliers.” John Herschel, too, saw a “very fine large cluster, all resolved into stars of 10th to 13th magnitude. It fills 1½ fields, but the straggling stars extend very far. There may be 500 stars.” Heinrich d'Arrest even believed he saw “wonderful loops and curved star patterns,” while Mädler remarked: “no particular compression can be noticed toward the middle.”

Leo Brenner described M 37 in detail in his observing guide for amateur astronomers, about 100 years ago: “A splendid object for small scopes. Visible already in small finder scopes as a nebulous star, 24′ diameter. The larger the telescope, the more splendid the view. With a 27-inch telescope, I estimated the number of visible stars 10th to 14th magnitude to about 600, but also in a 7-inch we see about 550, and a 4-inch at 120× magnification still shows nearly 500. Stars are more crowded towards the middle.”