M106, mag. +8.5, is a large spiral galaxy located in Canes Venatici that was discovered by Pierre Méchain in July 1781. He described it in little detail, referring to nothing more than a nebula close to star 3 Canum Venaticorum. It was rediscovered by William Herschel on March 9, 1788. Since Herschel was using a better telescope, he was able to see much more detail and noted it as "very brilliant with a bright nucleus and faint milky branches north preceding and south following." Although not one of Messier's final catalogue entries, this galaxy was included by Helen Sawyer Hogg in 1947 along with M105 and M107. It's reasonable to assume that all three were intended for addition by Méchain and Messier.
M106 is one of the brightest examples of a Seyfert type II galaxy and is therefore a strong X-ray emitter with unusual emission lines, which are believed to result from sections of the galaxy falling into the central supermassive black hole. American astronomer Carl Seyfert first identified this class of object in 1943.
This galaxy is located towards the northwestern corner of Canes Venatici, a faint constellation with only one reasonably bright star, Cor Caroli (α CVn - mag. +2.9). However, locating M106 is not difficult as the Plough or Big Dipper asterism of Ursa Major acts as a useful starting point. Focus on Megrez (δ UMa - mag. +3.2) the faintest star of the Plough and then move 5.5 degrees south and slightly east to reach 5 Canum Venaticorum (mag. +4.8). M106 is located just over 4 degrees south of 5 Canum Venaticorum with star 3 Canum Venaticorum (mag. +5.3) positioned halfway between them.
M106 is best seen from the Northern Hemisphere during the months of March, April and May. From southern temperate latitudes, it's a difficult object that never rises particularly high above the northern horizon.
M106 covers 19 x 7 arc minutes of apparent sky. Despite being spread over such a large area it has a remarkably high surface brightness and therefore within binocular range, appearing as a faint smudge. An 80mm (3.1-inch) refractor reveals a diffuse streak of light with a slightly brighter core, which looks like a galaxy. Larger 200mm (8-inch) reflectors enhance the view with more subtle details visible including dusty markings and a faint outer halo of nebulosity. Even larger amateur scopes reveal the galaxy's spiral shape.
Located at a distance of 25 million light-years from Earth, M106 is intrinsically large with a diameter of 135,000 light-years. It contains at least 400 billion stars. In August 1981, a 16th magnitude supernova (1981K) was observed in the galaxy.
M106 Data Table
|Object Type||Spiral galaxy|
|Distance (light-years)||25 Million|
|RA (J2000)||12h 18m 57s|
|DEC (J2000)||+47d 18m 15s|
|Apparent Size (arc mins)||18.6 x 7.2|
|Number of Stars||>400 Billion|
|Notable Feature||Seyfert II galaxy|