From Wikipedia, the free encyclopedia
Jump to navigationJump to search
"Galaxy M31" redirects here. For the smartphone, see Samsung Galaxy M31.Andromeda Galaxy
The Andromeda Galaxy with satellite galaxiesM32 (center left above the galactic nucleus) and M110 (center left below the galaxy)Observation data (J2000epoch)Pronunciation/ænˈdrɒmɪdə/ConstellationAndromedaRight ascension00h 42m 44.3s[1]Declination+41° 16′ 9″[1]Redshiftz = −0.001004 (minus sign indicates blueshift)[1]Helio radial velocity−301 ± 1 km/s[2]Distance765 kpc (2.50 Mly)[3]Apparent magnitude (V)3.44[4][5]Absolute magnitude (V)−21.5[a][6]CharacteristicsTypeSA(s)b[1]Mass(1.5±0.5)×1012[7]M☉Number of stars~1 trillion (1012)[10]Size46.56 kpc (152 kly)
(diameter; 25.0 mag/arcsec2 B-band isophote)[1][8][b]Apparent size (V)3.167° × 1°[1]Other designationsM31, NGC 224, UGC 454, PGC 2557, 2C 56 (Core),[1] CGCG 535-17, MCG +07-02-016, IRAS 00400+4059, 2MASX J00424433+4116074, GC 116, h 50, Bode 3, Flamsteed 58, Hevelius 32, Ha 3.3, IRC +40013The Andromeda Galaxy (IPA: /ænˈdrɒmɪdə/), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula, is a barred spiral galaxy with diameter of about 46.56 kiloparsecs (152,000 light-years)[8] approximately 2.5 million light-years (765 kiloparsecs) from Earth and the nearest large galaxy to the Milky Way. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at 1 trillionsolar masses (2.0×1042 kilograms). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%. This has been called into question by a 2018 study that cited a lower estimate on the mass of the Andromeda Galaxy,[11] combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way.[12][13] The Andromeda Galaxy has a diameter of about 46.56 kpc (152,000 ly), making it the largest member of the Local Group in terms of extension.The Milky Way and Andromeda galaxies are expected to collide in around 4–5 billion years,[14] merging to potentially form a giant elliptical galaxy[15] or a large lenticular galaxy.[16] With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects,[17] and is visible to the naked eye from Earth on moonless nights,[18] even when viewed from areas with moderate light pollution.