M31 - ANDROMEDA GALAXY

The Andromeda Galaxy (M31) is the nearest major galaxy to the Milky Way and the most distant object visible to the naked eye, located approximately 2.54 million light-years from Earth in the constellation Andromeda. It is a massive barred spiral galaxy containing an estimated one trillion stars and spanning about 220,000 light-years in diameter, making it the largest galaxy in the Local Group, which also includes the Milky Way and about 80 smaller galaxies. M31 has been known since antiquity and was described by the Persian astronomer Abd al-Rahman al-Sufi in 964 AD as a "small cloud." It was first telescopically observed by Simon Marius in 1612, and later cataloged by Messier in 1764. The Andromeda Galaxy played a pivotal role in the history of astronomy when Edwin Hubble identified Cepheid variable stars within it in 1924, definitively proving that it lay far beyond the boundaries of our own Milky Way and establishing the existence of other galaxies in the universe. M31 is approaching the Milky Way at about 110 kilometers per second, and the two galaxies are expected to collide and merge in approximately 4.5 billion years, eventually forming a single giant elliptical galaxy sometimes called "Milkomeda." The galaxy is accompanied by several satellite galaxies, including M32 and M110, which are visible in the same telescopic field. For observers, M31 is visible to the naked eye as an elongated smudge of magnitude 3.4 spanning over 3 degrees of sky. Binoculars reveal its bright nucleus and extended disk, while telescopes show dust lanes, star-forming regions, and the satellite galaxies.

Contains approximately one trillion stars spanning 220,000 light-years in diameter at a distance of 2.54 million light-years, the largest Local Group galaxy.