M106, mag. +8.5, is a large spiral galaxy located in Canes Venatici that was discovered by Pierre Méchain in July 1781. He described the galaxy in little detail; referring to it only as a nebula close to star 3 CVn. William Herschel then rediscovered it on March 9, 1788. Since Herschel was using a better telescope than Méchain 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 Messiers original catalogue entries, M106 was included, along with M105 and M107 in 1947 by Helen Sawyer Hogg. It seemed reasonable to assume that Méchain had already intended to add these objects to a future edition.
M106 is one of the brightest examples of a Seyfert type II galaxy and is therefore strong in X-rays and unusual emission lines, which are believed to result from sections of the galaxy falling into the supermassive black hole located at the centre. American astronomer Carl Seyfert first identified this class of object in 1943.
The galaxy is located towards the northwestern corner of Canes Venatici; a faint constellation with only one star Cor Caroli (α CVn - mag. +2.9) that's brighter than magnitude +4.0. However, locating M106 is not difficult as the Plough or Big Dipper asterism of Ursa Major is positioned just to the north and can be used as a starting point. Once found, focus on Megrez (δ UMa - mag. +3.2) the faintest star of the Plough. Positioned 5.5 degrees south and slightly east of Megrez is 5 CVn (mag. +4.8). M106 is located just over 4 degrees south of 5 CVn with star 3 CVn (mag. +5.3) positioned along the line connecting the two.
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 as it never rises very 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 a relatively easy binocular target, appearing as a faint smudge. A 80mm (3.1-inch) telescope reveals it as a diffuse streak of light with a slightly brighter core that looks like a galaxy. A larger 200mm (8-inch) scope enhances the view with more subtle details visible including dusty markings and a faint outer halo of nebulosity. The largest of 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.
M106 Data Table
|Object Type||Spiral galaxy|
|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|