M108 is a nice edge on barred spiral galaxy located in Ursa Major that was discovered by Pierre Méchain on February 19, 1781. It's not one of the objects included by Messier in his final published catalogue but was added much later by Owen Gingerich in 1953. This was based on analysis of notes written by Messier and Méchain, suggesting that it was intended for inclusion in a later version. William Herschel independently rediscovered the galaxy on April 17, 1789.
Locating M108 is easy as it's positioned 1.5 degrees southeast of bright Merak (β UMa - mag. +2.3). This star marks the southwestern corner of the bowl of the Plough or Big Dipper asterism of Ursa Major. Located 50 arc minutes southeast of M108 is planetary nebula M97 (Owl Nebula) and both items fit easily in the same telescopic wide field of view.
M108 is best seen from Northern Hemisphere latitudes during the months of March, April and May. For observes located at latitudes greater than 35N, it's circumpolar and therefore never sets.
The galaxy shines at apparent magnitude +10.2 and since it's almost edge-on from our perspective it has a high surface brightness. M108 can be spotted with small 80mm (3.1-inch) refractors, appearing as a faint strongly elongated streak of light with a slightly brighter core. Larger 200mm (8-inch) reflectors reveal a well-defined thin needle structure with a mottled dusty complexion and subtle variations in brightness. M108 is a galaxy that can take high magnifications well and is somewhat similar in appearance to M82.
In total, M108 spans 8.6 x 2.4 arc minutes of apparent sky and is located 45 million light-years from Earth. This corresponds to an actual diameter of 110,000 light-years. It's estimated to contain 400 billion stars and is believed to be an isolated member of the Ursa Major Cluster of galaxies.
A type II supernova (1969B) was observed in M108 on January 23, 1969. It peaked at magnitude +13.9.
M108 Data Table
|Object Type||Barred Spiral galaxy|
|Distance (light-years)||45 Million|
|RA (J2000)||11h 11m 31s|
|DEC (J2000)||+55d 40m 24s|
|Apparent Size (arc mins)||8.6 x 2.4|
|Number of Stars||400 Billion|