M82 is a superb irregular galaxy of high surface brightness that's visible with binoculars and located in the constellation of Ursa Major. It has an apparent magnitude of +8.4 and is separated by only 38 arc minutes from M81 an even brighter and equally - if not more - stunning galaxy. However, these two fine galaxies are very different objects indeed. M81 (mag. +6.9) when viewed from Earth appears almost face-on and is of the grand spiral deign; a galaxy that exhibits prominent near perfect and well defined spiral arms. On the other hand, M82 (mag. +8.4) is edge on, appearing long and thin and as a result is often referred to as the "Cigar" galaxy. Unlike the perfectly formed spiral shape of M81, M82 is irregular and classified as the prototype starburst galaxy in which stars are forming at exceptionally high rates.
These two objects are the largest members of the Ursa Major or M81 group of galaxies, which at a distance of 11.7 million light years is one of the closest groups of galaxies beyond our own Local Group. In space M81 and M82 are physically close, separated by only about 150,000 light years and when seen through binoculars and telescopes at low magnifications they form a striking pair that appear in the same optical field of view.
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 M82 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 directly north of M81.
M82 appears as a faint thin rod of light in binoculars with M81 visible as a large diffuse hazy patch. It's noticeable the different sizes and shapes of these two great galaxies. A small 80mm (3.1-inch) telescope at low power shows M82 as a slim gray needle of uniform light whereas at high magnifications, a 150mm (6-inch) or 200mm (8-inch) instrument reveals dusty patches that cross the sharp surface of M82. The centre region appears brighter that the edges.
In total M82 covers 11.2 x 4.3 arc minutes of apparent sky. At a distance of 11.5 million light-years, this corresponds to an actual diameter of 38,000 light-years; less than half the 90,000 light-years of M81. Together the pair forms a popular visual and imaging target for amateur astronomers that 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.
M82 is believed to contain at least 30 billion stars. On January 21, 2014, a bright Type 1a supernova (SN 2014J) was discovered in M82 by Stephen J. Fossey and his students at the University College London (UCL) observatory in London.
M82 Data Table
|Object Type||Starburst galaxy|
|RA (J2000)||09h 55m 51s|
|DEC (J2000)||69d 40m 43s|
|Apparent Size (arc mins)||11.2 x 4.3|
|Number of Stars||>30 Billion|
|Notable Features||Prototype starburst galaxy. Member of the M81 Group of galaxies|