M37 is the brightest, largest and richest of the three Messier open clusters located in the constellation of Auriga (the other two are M36 and M38). It's an impressive cluster that shines at magnitude +6.0 and is visible to the naked eye from dark sites. M37 is often referred to as one of the finest open clusters in the northern section of the sky. It's best seen from the Northern Hemisphere during the months of December, January and February.
The Italian astronomer Giovanni Battista Hodierna discovered M37 sometime before 1654. French astronomer Guillaume Le Gentil rediscovered M36 and M38 in 1749, but surprisingly failed to spot the brighter M37. It was left to Charles Messier to independently rediscover M37, which he did so on September 2, 1764.
As with M36 and M38, M37 is not difficult to find once you're familiar with the northern constellation of Auriga, the Charioteer. Auriga is a medium size constellation with an area of 657 square degrees and ranks as 21st largest of the 88 constellations in the sky. It's positioned northeast of Taurus and northwest of Gemini. As well as home to a number of bright open clusters, it contains the brilliant spectroscopic binary star Capella, which at mag. +0.08 is the 6th brightest star in the night sky. Auriga is a polygon shaped constellation, with Capella located at the northern point. Located 7.5 degrees to the east of Capella is Menkalinan (β Aur - mag. +1.9) and 8 degrees due south of Menkalinan is θ Aur (mag. +2.65). From θ Aur, draw an imaginary line in a southwesterly direction for 11 degrees until you reach another bright star. This star is El Nath (β Tau - mag. +1.65), which straddles the border between Auriga and Taurus. Located just east of the mid-point of the line connecting θ Aur and El Nath is M37. Unlike M36 and M38, M37 is located on the outside of the main Auriga polygon.
Of the three Messier clusters in Auriga, M37 along with M36 can be spotted with the naked eye from dark sites, appearing as faint patches of light. M38 shines about a magnitude fainter and is beyond naked eye visibility. Together with M36 and M38, all three are easily seen with good binoculars. A pair of 10x50s depicts M37 as a large hazy, almost nebula like patch of light.
When viewed through larger 20x80 binoculars, M37 appears as a very compact cluster. The brightest stars are just about resolvable, especially when using averted vision. A small 100mm (4-inch) telescope reveals about a dozen or so tenth magnitude stars concentrated towards the centre of the cluster. With averted vision, tens of more stars are visible with the cluster taking on a mottled appearance. The stars appear faint and surrounded by a misty cloak of haze, giving the impression of a sprinkling of diamonds or stardust! A bright orange star towards the center of the cluster is apparent.
At about 100x magnification through a 200 mm (8-inch) scope, M37 fills a good proportion of the field of view with hundreds of stars visible. The cluster appears wedged, triangular or even oblong shaped and covers 24 arc minutes of sky. It's believed the cluster contains at least 150 stars brighter than 12th magnitude and probably more than 500 stars in total. Larger telescopes resolve M37 further, showing hundreds of mostly white stars, but also bluish-white stars, orange-red stars and even some yellow ones. The cluster is a sensational sight in all types of optical instruments.
M37 is a superb open cluster located in the constellation of Auriga. It's brighter and much richer than neighbouring M36 and M38 and faintly visible to the naked eye. Even a small 80mm (3.1-inch) telescope will start to resolve some of the stars, with hundreds more visible in larger scopes. M37 is located 4,400 light-years from Earth, which corresponds to a spatial diameter of about 30 light-years. It is estimated to be 300 million years old.
M37 Data Table
|Object Type||Open Cluster|
|RA (J2000)||05h 52m 18s|
|DEC (J2000)||+32d 33m 11s|
|Apparent Size (arc mins)||24 x 24|
|Age (years)||300 Million|
|Number of Stars||>150|
|Other Name||Collinder 75|