M81 or Bode's galaxy is a large bright spiral galaxy located 11.8 million light-years from Earth in the constellation of Ursa Major. With an apparent magnitude of +6.9 it's easily visible with binoculars, a fine target for small telescope owners and a wonderful sight in larger scopes. The galaxy is a striking example of a grand design spiral; a galaxy that exhibits prominent near perfect and well defined spiral arms.
In the same binocular and low magnification telescope field of view as M81 is M82, another prominent galaxy. At mag. +8.4, M82 is fainter (and smaller) than M81 and a very different type of galaxy. It's a starburst galaxy in which stars are forming at exceptionally high rates. Also known as the "Cigar" galaxy, M82 is the prototype object of its type and provides a striking compliment to the near perfect spiral shape of M81. Together the pair forms a popular visual and imaging target for amateur astronomers.
Both M81 and M82 were discovered by Johann Elert Bode on December 31, 1774. Pierre Mechain then independently rediscovered both galaxies in August 1779. He reported his observations to Charles Messier who added them to his catalogue on February 9, 1781.
Finding M81 is not particularly difficult as the famous "Plough" asterism of Ursa Major can be used as the starting point. First focus on Dubhe (α UMa - mag. +1.8) the northwest corner star of the bowl of the Plough. The M81 / M82 pair is located 10 degrees northwest of this star with M82 positioned 38 arc minutes directly north of M81.
M81 appears a faint patch of light in 7x50 or 10x50 binoculars. There are rare reports that some eagle-eyed stargazers have managed, under exceptional conditions, to see M81 with the naked eye but this is sensational viewing by all accounts. It would mean M81 being by far the most distant permanent object that can be viewed without a telescope. However, M33 is commonly regarded as the holder of this record.
A small 80mm (3-inch) scope at low power reveals M81 as a bright oval haze without detail. Also visible and in the same field of view is M82, which appears as a slim grey needle of uniform light. A 150mm (6-inch) scope at high power reveals M81 as a huge low surface brightness halo of nebulosity surrounding a bright core. In larger scopes more subtle details can be seen. The small unbarred spiral galaxy NGC 2976 lies 1.5 degrees southwest of M81 and can be seen without detail through a 200mm telescope.
M81 has an apparent size of 27 x 14 arc minutes, which corresponds to a spatial diameter of 90,000 light-years. It's estimated to contain more than 250 billion stars and is the largest member of the Ursa Major or M81 group of galaxies that contains at least 34 members. M82 is also a member of this group, which is one of the closest groups of galaxies beyond our own Local Group. The galaxies are best seen from the Northern Hemisphere during the months of March, April and May. They are circumpolar and hence never set from locations north of 21 degrees north.
Only one supernova, SN 1993J, has been detected in M81. It was discovered by F. Garcia in Spain on March 28, 1993 and peaked at apparent magnitude +10.8, making it the brightest supernova in the northern part of the sky since 1954.
M81 Data Table
|Object Type||Spiral galaxy|
|RA (J2000)||09h 55m 33s|
|DEC (J2000)||69d 03m 55s|
|Apparent Size (arc mins)||26.9 x 14.1|
|Number of Stars||>250 Billion|
|Notable Feature||Largest member of the M81 Group of galaxies|