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 (after M32). The galaxy is classified as Hubble type E5 and designated as peculiar, due to unusual dark structures that are probably caused by dust clouds.
At magnitude +8.7, M110 is a challenging binocular object. It covers 22 x 11 arc minutes but suffers from low surface brightness and therefore even a small amount of light pollution can render it invisible. Surprisingly, Charles Messier never included it in his famous list. However he depicted it, together with M32, on a drawing of the Andromeda galaxy that he made on August 10, 1773. Caroline Herschel independently rediscovered the galaxy on August 27, 1783. Much later in 1967, Kenneth Glyn Jones suggested assigning 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 designation, NGC 205.
To find M110, first locate the Andromeda Galaxy, which is positioned northeast of the Great Square of Pegasus. Of the four stars of the square only three of them actually belong to Pegasus. The northeast corner star, Alpheratz (α And - mag. +2.1), is part of neighbouring Andromeda. Located 7 degrees northeast of Alpheratz is δ Andromedae (mag. +3.3) and a further 8 degrees to the northeast is Mirach (β And - mag. +2.1). The Andromeda galaxy is another 8 degrees northwest of Mirach at the end of a line connecting μ Andromedae with ν Andromedae. M110 is positioned 36 arc minutes northwest of the centre of M31.
The galaxies are best seen from the Northern Hemisphere locations during the months of September, October and November.
Through 80mm (3.1-inch) refractors, M110 appears dim and diffuse. It has a soft, low luminosity without a bright core (unlike M31 and M32). With 200mm (8-inch) reflectors, it 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 away, which is about 150,000 light-years further from us than M31. Its actual diameter is 17,000 light-years and it's estimated to contain 10 billion stars. Surrounding M110 are at least 8 globular clusters, the brightest of which (G73) is of 15th magnitude and visible in very large amateur reflectors. In 1999, R. Johnson and M. Modjaz of the University of California at Berkeley discovered a nova in M110, which peaked at magnitude +18.
M110 Deep Sky Data Table
|Object Type||Dwarf elliptical galaxy|
|Distance (light-years)||2.69 Million|
|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|