Messier 38 is an open cluster

Open cluster

An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...

 in the Auriga constellation.

It was discovered by Giovanni Batista Hodierna before 1654 and independently found by Le Gentil in 1749. M36

Messier 36

Open Cluster M36 is an open cluster in the Auriga constellation. It was discovered by Giovanni Batista Hodierna before 1654. M36 is at a distance of about 4,100 light years away from Earth and is about 14 light years across. There are at least sixty members in the cluster...

 and M37

Messier 37

Messier 37 is the richest open cluster in the constellation Auriga. It was discovered by Hodierna before 1654....

, also discovered by Hodierna, are grouped together with M38 at a distance of about 3,420 light years away from Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

.

The cluster's brightest stars form a pattern resembling the Greek letter Pi

Pi (letter)

Pi is the sixteenth letter of the Greek alphabet, representing . In the system of Greek numerals it has a value of 80. Letters that arose from pi include Cyrillic Pe , Coptic pi , and Gothic pairthra .The upper-case letter Π is used as a symbol for:...

 or, according to Webb, an "oblique cross." At its distance of 4,200 light years, its angular diameter of about 20' corresponds to about 25 light years, similar to that of its more distant neighbor M37

Messier 37

Messier 37 is the richest open cluster in the constellation Auriga. It was discovered by Hodierna before 1654....

. It is of intermediate age (about 220 million years, according to Sky Catalog 2000) and features a yellow giant of apparent magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 +7.9 and spectral type G0 as its brightest member. This corresponds to an absolute magnitude

Absolute magnitude

Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...

 of -1.5, or a luminosity of 900 suns. For comparison, the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 would appear as a faint magnitude +15.3 star from the distance of M38.

Walter Scott Houston

Walter Scott Houston

Walter Scott Houston was an American popularizer of amateur astronomy. He wrote the "Deep-Sky Wonders" column in Sky and Telescope magazine from 1946 to 1993.-Biography:...

 described its appearance as follows:

Photographs usually show a departure from circularity, a feature quite evident to visual observers. Older reports almost always mention a cross shape, which seems more pronounced with small instruments. A view with a 24-inch reflector on a fine Arizona night showed the cluster as irregular, and the host of stars made fruitless any effort to find a geometrical figure.

Components

NAME	Right ascension Right ascension Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...	Declination Declination In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...	Spectral type
HD 35519 HD 35519 HD 35519 is a star in star clusters NGC 1912 and NGC 1907.-References:* *...	05h 26m 54.3176s	+35° 27' 26.181	K2
NGC 1912 HOAG 2			B5II-III
NGC 1912 HOAG 3
NGC 1912 HOAG 4	05h 28m 35.39s	+35° 52' 51.2	A0V
NGC 1912 HOAG 5	05h 28m 50.73s	+35° 46' 47.2	A0Vn
NGC 1912 HOAG 6	05h 28m 10.46s	+35° 55' 26.0	A0:V
NGC 1912 HOAG 7	05h 28m 34.25s	+35° 53' 29.7	A2V
NGC 1912 HOAG 11
NGC 1912 HOAG 19			K2IIIb
NGC 1912 HOAG 104			G5III
NGC 1912 SS G2
NGC 1912 HOAG 128			K0III
NGC 1912 SS G4			A5:V
NGC 1912 HOAG 153			K0V
NGC 1912 SS G3			A3V
NGC 1912 HOAG 160			K1IV
NGC 1912 HOAG 161			G5V
NGC 1912 HOAG 171			G7IV
NGC 1912 HOAG 172