M110 is a dwarf elliptical galaxy located in the constellation of Andromeda. It's one of many satellite galaxies orbiting M31, the famous and spectacular Andromeda galaxy. Of these, at least 14 are dwarf galaxies with M110 being the second brightest of them (after M32). The galaxy is classified as Hubble type E5 and designated as "peculiar" due to unusual dark structures that are probably due to dust clouds.
At magnitude +8.7, M110 is a very challenging binocular object. Although quite large - it covers 22 x 11 arc minutes of apparent sky - it suffers from a low surface brightness and hence even a small amount of light pollution can render it a difficult object to spot with small telescopes.
Surprisingly, Charles Messier never included M110 in his famous list. However he depicted it, together with M32 on a drawing of the Andromeda galaxy he made on the August 10, 1773. Caroline Herschel independently discovered the galaxy on August 27, 1783 and much later in 1967, Kenneth Glyn Jones suggested assigning the galaxy a Messier number. Although now commonly known as M110, it's still often referred to in many texts and charts by its New General Catalogue number, NGC 205.
To find M110, first locate the Andromeda Galaxy, which is positioned northeast of the famous "Great Square of Pegasus". Of the four stars of the square, only three of them actually belong to Pegasus. The northeast corner star and brightest of the four at magnitude 2.1, Alpheratz (α And) is part of neighbouring Andromeda. Located 7 degrees to the northeast of Alpheratz is δ And (mag. 3.3) and a further 8 degrees to the northeast of δ And is mag. 2.1, Mirach (β And). The Andromeda galaxy is a further 8 degrees to the northwest of Mirach at the end of a line connecting Mirach with μ And and ν And. M110 is located 36 arc minutes northwest of the centre of M31.
The galaxies are best seen from the Northern Hemisphere during the months of September, October and November.
In a 80mm (3.1 inch) telescope M110 appears very dim and diffuse. It has a soft, low luminosity without a bright point core (unlike M31 and M32). In a 200mm (8-inch) scope, M110 appears as a large oval nebulosity that's slightly brighter towards the centre. The edges are diffuse.
M110 is located 2.69 million light-years from Earth, which is about 150 million light-years further from us than M31. Its actual diameter is 17,000 light-years and the galaxy is estimated to contain 10 billion stars. Surrounding M110 are at least 8 globular clusters, the brightest of them (G73) is of 15th magnitude which is visible in very large amateur telescopes. In 1999, R. Johnson and M. Modjaz of the University of California at Berkeley on behalf of the Lick Observatory Supernova search discovered a nova in M110 at magnitude +18.
M110 Deep Sky Data Table
|Object Type||Dwarf elliptical galaxy|
|RA (J2000)||00h 40m 22s|
|DEC (J2000)||41d 41m 26s|
|Apparent Size (arc mins)||21.9 x 11.0|
|Number of Stars||10 Billion|
|Notable Feature||Satellite galaxy of M31|