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M 36
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M 36

February 18, 2005
Open Cluster M36 (NGC 1960), type 'f', in Auriga

Right Ascension: 05 : 36.1 (h:m)
Declination: +34 : 08 (deg:m)
Distance: 4.1 (kly)
Visual Brightness: 6.3 (mag)
Apparent Dimension: 12.0 (arc min)

Discovered by Giovanni Batista Hodierna before 1654.

This is the first of three bright open clusters in the southern part of constellation Auriga, included in Messier's catalog (the other two are M37 and M38). All 3 have been first recorded by Giovanni Batista Hodierna before 1654, as pointed out by Kenneth Glyn Jones; however these discoveries came to light as late as 1984, so that Le Gentil has independently rediscovered it. Charles Messier included it in his catalog on September 2, 1764.

M36 is about 4,100 light years distant (only Kenneth Glyn Jones disagrees and has 3,700), so that its angular diameter of 12' corresponds to about 14 light years (Wallenquist gives an apparent diameter of 19', corresponding to over 20 light years). It has about 60 proven members, the brightest of which are of apparent mag 9 and spectral type B2; the luminosity of the brightest member is about 360 times that of the Sun. Many of these bright stars are rapidly rotating, as shown by their broadened spectral lines, an effect which is also found for the bright type B members of the Pleiades (M45). If it were at the same distance (i.e., 10 times closer), this cluster would look as conspicuous as and very similar to the Pleiades.

As it is quite young (about 25 million years), it contains no red giants, in contrast to its neighbors M37 and M38, which lie roughly at the same distance. M36 was classified as of Trumpler type I,3,m (Sky Catalog 2000) or I,3,r (Götz).