Messier 81 - Bode's Galaxy
Messier 81 is a beautiful spiral galaxy in the constellation "Big Dipper", discovered on New Year's Eve 1774 by the German astronomer "Johann Elert Bode"
and sometimes called "Bode's Galaxy" in his honor. The galaxy has a visual magnitude of 7.0mag and an apparent size of 24.9'x11.5' - so it is almost as large
as the crescent moon.
Together with 33 other galaxies "Bode's Galaxy" belongs to the "M81- Group", which also includes Messier 82 and NGC 3077. All three mentioned galaxies
interact with each other and are even connected by gas filaments. Some of these filaments fall into the centers of M82 and NGC 3077 and cause there a
strongly increased star formation (star burst).
With a diameter of about 96,000 light-years, Messier 81 is only slightly smaller than our Milky Way and belongs to the group of Hubble-type "SAb" spiral
galaxies. It is home to 200 billion stars and countless HII regions, which are mainly found in the spiral arms. The center is dominated by an enormous
black hole with a mass of 70 million solar masses, a so-called SMBH (Supermassive Black Hole). The galaxy is surrounded by a halo of more than 200
globular clusters. So far only one supernova has been observed in M81, namely "SN 1993J" with a maximum brightness of 10.7mag.
Right next to Messier 81 is a small irregular dwarf galaxy called "Holmberg IX", which has an apparent magnitude of 14.5mag and is only 2.5'x2' in size.
The true diameter is about 9,000 light-years. Since 20% of all stars were formed within the last 200 million years, "Holmberg IX" is one of the youngest
galaxies in the near vicinity.
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With my 20" telescope Messier 81 offers a stunning sight under very dark skies. At a magnification of 120x the narrow and filigree spiral arms are wonderful
to see and even reveal some structures like brighter spots. The eastern spiral arm (left) appears brighter than the western one.
By increasing the magnification to 270x you can search for HII regions in the spiral arms - I could find 8 of them. The three HII- regions in the south of Messier
81 (bottom) were the easiest to see and not very difficult with indirect vision. The HII regions in the northern part were much more difficult.
Not on the drawing is "Holmberg IX", a small dwarf galaxy, which appears with indirect vision as a pale, homogeneous light spot.
