m31 Andromeda galaxy

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Andromeda Galaxy

The Andromeda Galaxy

Observation data (J2000 epoch)
Pronunciation /


Constellation Andromeda
Right ascension 00h 42m 44.3s[1]
Declination +41° 16′ 9″[1]
Redshift z = −0.001
(minus sign
indicates blueshift)
Helio radial velocity −301 ± 1 km/s[2]
Distance 2.54 ± 0.06 Mly(778 ± 17 kpc)[3][2][4][5][6][a]
Type SA(s)b[1]
Number of stars 1 trillion (1012) [7]
Apparent dimensions (V) 190′ × 60′[1]
Apparent magnitude (V) 3.44[8][9]
Other designations
M31, NGC 224, UGC 454, PGC 2557, 2C 56 (Core),[1] LEDA 2557
See also: Galaxy, List of galaxies

The Andromeda Galaxy (/ænˈdrɒmədə/) is a spiral galaxy approximately 2.6 million light-years (2.5×1019 km) from Earth[4] in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. The Andromeda galaxy is the nearest spiral galaxy to our galaxy (Milky Way), but not the closest galaxy overall. It gets its name from the area of the sky in which it appears, the Andromeda constellation, which was named after the mythological princess Andromeda. M31 is the largest galaxy of the Local Group, which also contains our galaxy (Milky Way), the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, the Andromeda galaxy may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and could be the most massive in the grouping.[10] The 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars:[7] at least twice the number of stars in our own galaxy, which is estimated to be 200–400 billion.[11]