Degree of difficulty 2 (of 5)

Minimum aperture Naked eye

Designation NGC 1912

Type Open cluster

Class II2r1

Distance 3500 ly (K2005)

Size 15 ly

Constellation Auriga

R.A. 5h 28.7min

Decl. +35° 51′

Magnitude 6.4

Surface brightness –

Apparent diameter 15′

Discoverer Hodierna, 1654

History M 38 was, as the other two Auriga clusters, discovered by Giovanni Batista Hodierna, before 1654, and was described by him as “nebulous patch.” Le Gentil, unaware of Hodierna's observations, made an independent discovery in 1749 and recognized M 38 as a star cluster. On the 25th of September 1764, Messier noted: “Cluster of faint stars, at small distance from the two previous clusters [M 36 and M 37], this one is of a squared shape and does not contain nebulosity, if examined with care in a good instrument. Its extent is about 15′.

Admiral Smyth saw “an oblique cross, with a pair of large stars in each arm, and a conspicuous single one at the center,” while John Herschel noticed the “irregular figure” and wrote: “large and small stars, very rich.” Leo Brenner's description comes astonishingly close to that of Messier: “In one field of view with NGC 1907, 15′ diameter, of irregular, rather squared shape, with bright central star, very large and rich, consists of many bright and fainter stars.”

Astrophysics Until recently, it was assumed that M 38 would have a distance of 4200 light-years, like M 36, and be its close neighbor in space, only 150 light-years away. While the interstellar extinction for both clusters is indeed about the same, around 1 magnitude, recent studies have nevertheless corrected the distance of M 38 downwards to 3500 light-years. The true diameter then becomes 15 light-years.

The brightest cluster star (magnitude 7.9) is a G0 giant with 900 times the solar luminosity.