Messier 81

Messier 81 (also known as NGC 3031 ) is a 7.0 like bright spiral galaxy of Hubble type Sb in the constellation Ursa Major. M81 is the galaxy in the northern sky, which appears to us after the Andromeda Galaxy and the Triangulum Galaxy largest and brightest. The number of stars of the system is estimated at 250 billion, which is a slightly smaller value compared to the Milky Way. M81 is sometimes in honor of its discoverer also known as Bode's Galaxy, since it was discovered on 31 December 1774 by Johann Elert Bode.

The apparent area of M81 does 26.9 ' 14.1 times ' from ( the moon has an apparent diameter of about 30') for about three percent of the area of the Andromeda nebula. With 12 million light-years, M81 is well four times as much as this galaxy away and thus appears noticeably smaller. The distance was determined as part of the H0 Key Projects in 1993 very accurate and is significantly larger than the values ​​of about 7 million light- years, which are often found in older literature.

From Earth, we cant see the galaxy that has relatively loose spiral arms, but many stars have in the city center. In the Hubble sequence M81 is of type Sb The structure of the galaxy can be seen better in the UV and IR spectral range.

IR absorption by SST, at 3.6 microns ( blue), 8 microns ( green) and 24 microns ( red)

In the far infrared absorbed by the Herschel space telescope

Amateur recording of M81 and M82

M81 is equipped with a brightness of 7.0 mag in the binoculars already clearly visible. In its vicinity there is the slightly fainter spiral galaxy M82. These two galaxies are at the core of the M81 group of galaxies that form a real physical group is the one of the nearest neighbors of our Local Group. This group includes, among others, yet NGC 2403, NGC 3077 and NGC 2976. In addition, Messier 81 has a small satellite galaxy, irregular galaxy UGC 5336 ( Holmberg IX).