M81 - Spiral Galaxy in Ursa Major


M81 (with NGC3077 bottom left) - Spiral Galaxy in Ursa Major
Mag 6.9 RA 9:55.6 Dec +69 04 21x10 arcminutes


Discovered by Johann Elert Bode in 1774.

M81 is one of the easiest and most rewarding galaxies to observe for the amateur astronomer on the northern hemisphere, because with its total visual brightness of about 6.8 magnitudes it can be found with small instruments.

The pronounced grand-design spiral galaxy M81 forms a most conspicuous physical pair with its neighbor, M82, and is the brightest and probably dominant galaxy of a nearby group called M81 group. A few tens of million years ago, which is semi-recently on the cosmic time scale, a close encounter occurred between the galaxies M81 and M82. During this event, larger and more massive M81 has dramatically deformed M82 by gravitational interaction. The encounter has also left traces in the spiral pattern of the brighter and larger galaxy M81, first making it overall more pronounced, and second in the form of the dark linear feature in the lower left of the nuclear region. The galaxies are still close together, their centers separated by a linear distance of only about 150,000 light years.

M81 is the first of the four objects originally discovered by Johann Elert Bode, who found it, together with its neighbor M82, on December 31, 1774. Bode described it as a "nebulous patch", about 0.75 deg away from M82, which "appears mostly round and has a dense nucleus in the middle," and included it as No. 17 in his list. Pierre Méchain independently rediscovered both galaxies as nebulous patches in August 1779 and reported them to Charles Messier, who added them to his catalog after his position measurement on February 9, 1781.

ST-10XME and CFW8a Astrodon LRGB
Takahashi FS102 with focal reducer for F/5.9
Self-guided on AP900 QMD
Luminance 18 x 2 min
RGB 3 x 2 min (I lost most of my colour data)
All images aligned and combined in Maxim using Russ Croman's sigma reject plug-in
Colour combines, Levels and Curves in PS CS2
Luminance layered in at 50% twice with saturation boost.
Image is cropped slightly from the full frame.

Click on the image to see a larger version.

Flesherton, Ontario
March 03 2006