Messier 110 — Galaxy in Andromeda

M110 (NGC 205) is a dwarf elliptical galaxy in the constellation Andromeda, located approximately 2.69 million light-years from Earth. It is one of the two prominent satellite galaxies of the great Andromeda Galaxy (M31), the other being M32. M110 is noticeably larger and more diffuse than the compact M32, spanning about 17,000 light-years across. Classified as a dwarf spheroidal galaxy (type E5 pec), M110 is unusual among elliptical galaxies because it contains dark dust clouds and shows evidence of recent star formation — features normally associated with spiral and irregular galaxies. Populations of young blue stars have been detected in its central regions, along with dark dust patches visible in deep images. M110 lies about 35 arcminutes northwest of M31's nucleus and is clearly visible as a separate object in photographs of the Andromeda Galaxy. Despite being gravitationally bound to M31, M110 has retained a modest globular cluster population of about eight clusters.

Located about 35 arcminutes northwest of the nucleus of the Andromeda Galaxy (M31). M110 is visible in binoculars as a faint, elongated smudge on the opposite side of M31 from M32. While M32 appears as a compact bright spot, M110 has a much lower surface brightness and appears as a diffuse, soft glow. A 4-inch telescope at 60-80x shows M110 as a large, oval haze oriented roughly north-south. An 8-inch telescope reveals its gradual brightening toward the center, with no sharp nucleus — a marked contrast to M32's stellar-like core. Dark dust lanes require 12 inches or more under excellent conditions. When observing M31, always take time to study both satellites and note their very different characters. Best observed from September through January.

M110 holds a unique distinction in the history of the Messier catalog: it was the very last object added, not being formally included until 1966 when Kenneth Glyn Jones proposed its addition. Charles Messier himself had observed and depicted the object — he clearly drew it on his illustration of M31 published in 1807 — but never assigned it a catalog number. The galaxy was independently discovered by Caroline Herschel on August 27, 1783, making it one of her significant contributions to deep-sky astronomy. The designation NGC 205 comes from John Dreyer's 1888 catalog. In modern times, M110 has been a key object for studying the puzzling phenomenon of recent star formation in elliptical galaxies, challenging the traditional view that ellipticals are 'dead' systems composed entirely of old red stars.