Andromeda Galaxy

Andromeda_Nebula_-_Isaac_Roberts,_29_December_1888

Andromeda_constellation_map

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Milky_Way_and_Andromeda_in_space,_to_scale

Hubble_Finds_Giant_Halo_Around_the_Andromeda_Galaxy

File:A Swift Tour of M31.ogv

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Spiral galaxy in the constellation Andromeda

{{Infobox | above = Andromeda Galaxy | image = {{#if:Andromeda Galaxy (with h-alpha).jpg|[[File:Andromeda Galaxy (with h-alpha).jpg|image=Andromeda Galaxy (with h-alpha).jpg|upright=1.3|alt=|suppressplaceholder=yes}} | caption = The Andromeda Galaxy | abovestyle = background: #ddd; | headerstyle = background: #ddd; | belowstyle = background: #ddd; | labelstyle = background: inherit;

|header1 = Observation data (J2000 epoch) | label2 = Pronunciation | data2 =

| label3 = Constellation | data3 = | label4 = Right ascension | data4 = 00h 42m 44.3s | label5 = Declination | data5 = +41° 16′ 9″

| label6 = Redshift | data6 = -0.001001 | label7 = Heliocentric radial velocity | data7 = | label8 = Galactocentric velocity | data8 = | label10 = Distance | data10 = 2.537 million | label11 = Group or cluster | data11 = | label12 = Apparent magnitude (V) | data12 = 3.44 | label13 = Apparent magnitude (B) | data13 = | label14 = Absolute magnitude (V) | data14 = | label15 = Absolute magnitude (B) | data15 = | label16 = Surface brightness | data16 = | label17 = magnitude (J) | data17 = | label18 = magnitude (H) | data18 = | label19 = magnitude (K) | data19 =

|header20 = Characteristics | label21 = Type | data21 = SA(s)b | label22 = Mass | data22 = | label23 = Mass/Light ratio | data23 = | label24 = Number of stars | data24 = | label25 = Size | data25 = | label26 = Apparent size (V) | data26 = 3.167° × 1° | label27 = Half-light radius (physical) | data27 = | label28 = Half-light radius (apparent) | data28 = | label29 = H I scale length (physical) | data29 = | label30 = H I scale length (apparent) | data30 = | label31 = X-ray radius (physical) | data31 = | label32 = X-ray radius (apparent) | data32 =

| label35 = Notable features | data35 = Nearest spiral galaxy to the Milky Way

| data38 =

|header40 = Other designations | data41 = M31, NGC 224, UGC 454, PGC 2557

| data43 =

| belowclass = noprint }}

The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 2.537 million light-years from Earth. It is the nearest spiral galaxy to the Milky Way and the largest galaxy in the Local Group, which also contains the Milky Way, the Triangulum Galaxy (M33), and about 54 other smaller galaxies.

Discovery and Observation

The Andromeda Galaxy is named after the constellation of Andromeda, where it appears. It is visible to the naked eye from Earth on clear nights, appearing as a faint, diffuse smudge of light. The galaxy was first cataloged by the Persian astronomer Abd al-Rahman al-Sufi in 964 AD in his Book of Fixed Stars. It was later observed by Simon Marius in 1612 and described as a "small cloud."

Structure and Composition

The Andromeda Galaxy is a barred spiral galaxy with a diameter of about 220,000 light-years, making it the largest galaxy in the Local Group. It contains approximately one trillion stars, more than twice the number of stars in the Milky Way. The galaxy has a prominent central bulge and a well-defined spiral structure with several spiral arms.

Nucleus

The nucleus of the Andromeda Galaxy contains a supermassive black hole with a mass estimated to be around 100 million times that of the Sun. The central region is densely packed with stars, and it exhibits significant star formation activity.

Halo

The galaxy has a large halo of hot gas and dark matter, extending several hundred thousand light-years from its center. This halo contains numerous globular clusters and satellite galaxies, including M32 and M110.

Interaction with the Milky Way

The Andromeda Galaxy is on a collision course with the Milky Way, with a predicted merger occurring in about 4.5 billion years. This event will likely result in the formation of a new galaxy, sometimes referred to as "Milkomeda" or "Milkdromeda."

Related Pages

• Milky Way
• Triangulum Galaxy
• Local Group
• Spiral galaxy
• List of nearest galaxies

See Also

• List of Messier objects
• List of galaxies

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