Messier 110, or M110, also known as NGC 205, is a dwarf elliptical galaxy that is a satellite of the Andromeda Galaxy. Although Charles Messier never included the galaxy in his list, it was depicted by him, together with M32, on a drawing of the Andromeda Galaxy; a label on the drawing indicates that Messier first observed NGC 205 on August 10, 1773. The galaxy was independently discovered by Caroline Herschel on August 27, 1783; her brother William Herschel described her discovery in 1785. The suggestion to assign the galaxy a Messier number was made by Kenneth Glyn Jones in 1967, making it the last member of the Messier List. This galaxy has a morphological classification of pec dE5, indicating a dwarf elliptical galaxy with a flattening of 50%. M110 is designated peculiar because there are patches of dust and young blue stars located near the center. This is unusual for dwarf elliptical galaxiesin general, and the reason for this peculiarity is unclear. Unlike M32, NGC 205 does not show evidence for a supermassive black hole at its center. The interstellar dust in M110 has a mass of with a temperature of, and the interstellar gas has. The inner regions of M110 show a deficiency in the interstellar medium materials, which most likely were ejected by supernova explosions. Tidal interactions with M31 may have stripped away a significant fraction of the expelled gas and dust, leaving the galaxy as a whole deficient in its IM density. A few novae have been detected in this galaxy, including one discovered in 1999, and another detected in 2002. The latter, designated EQ J004015.8+414420, had also been captured in images taken by the Sloan Digital Sky Survey in October, 2002. About half of the Andromeda's satellite galaxies are orbiting the host galaxy along a highly flattened plane, with 14 out of 16 following the same sense of rotation. One theory proposes that these objects once belonged to a subhalo surrounding NGC 205, then the group was broken up by tidal forces during a close encounter with Andromeda.
