Andromeda Galaxy

AndromedaM31Andromeda NebulaMessier 31Andromeda "nebulagalaxyGreat Andromeda NebulaM 31M31 (Andromeda Galaxy)224
The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula (see below), is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way.wikipedia
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Local Group

Local ClusterLocal group of galaxiesLG
The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass.
It consists of two clusters of galaxies in a "dumbbell" shape, the Milky Way and its satellites on one hand, and the Andromeda Galaxy and its satellites on the other.

Andromeda (constellation)

AndromedaAndromeda constellationAndromedae
The galaxy's name stems from the area of the Earth's sky in which it appears, the constellation of Andromeda.
The constellation's most obvious deep-sky object is the naked-eye Andromeda Galaxy (M31, also called the Great Galaxy of Andromeda), the closest spiral galaxy to the Milky Way and one of the brightest Messier objects.

Messier object

MessierMessier CatalogueList of Messier objects
With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects making it visible to the naked eye from Earth on moonless nights, even when viewed from areas with moderate light pollution.
For example, Messier 1 is a supernova remnant, known as the Crab Nebula, and the great spiral Andromeda Galaxy is M31.

Milky Way

Milky Way Galaxygalaxyour galaxy
The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula (see below), is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way. In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe.
The low end of the estimate range is 5.8 solar masses, somewhat less than that of the Andromeda Galaxy.

Andromeda–Milky Way collision

collision of the Milky Way and Andromeda galaxiesMilkomedabegin to collide
The Milky Way and Andromeda galaxies are expected to collide in around 4.5 billion years, merging to form a giant elliptical galaxy or a large lenticular galaxy.
The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 4.5 billion years between two galaxies in the Local Group—the Milky Way (which contains the Solar System and Earth) and the Andromeda Galaxy.

Nebula

nebulaediffuse nebulanebulosity
He believed Andromeda to be the nearest of all the "great nebulae", and based on the color and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius, or roughly 18,000 light years.
The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.

SN 1885A

S AndromedaeS AndS Andromedae
In 1885, a supernova (known as S Andromedae) was seen in Andromeda, the first and so far only one observed in that galaxy.
SN 1885A (also S Andromedae) was a supernova in the Andromeda Galaxy, the only one seen in that galaxy so far by astronomers.

William Huggins

Sir William HugginsHugginsHuggins, Sir William
In 1864, William Huggins noted that the spectrum of Andromeda differed from that of a gaseous nebula.
He was also the first to distinguish between nebulae and galaxies by showing that some (like the Orion Nebula) had pure emission spectra characteristic of gas, while others like the Andromeda Galaxy had the spectral characteristics of stars.

Supernova

supernovaecore-collapse supernovasupernovas
In 1885, a supernova (known as S Andromedae) was seen in Andromeda, the first and so far only one observed in that galaxy.
The first such observation was of SN 1885A in the Andromeda Galaxy.

Naked eye

naked-eyeunaided eyenaked human eye
With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects making it visible to the naked eye from Earth on moonless nights, even when viewed from areas with moderate light pollution.
These include the Pleiades, h/χ Persei, the Andromeda Galaxy, the Carina Nebula, the Orion Nebula, Omega Centauri, 47 Tucanae, the Ptolemy Cluster Messier 7 near the tail of Scorpius and the globular cluster M13 in Hercules.

Walter Baade

W. BaadeBaadeBaade, Walter
In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy.
There, during World War II, he took advantage of wartime blackout conditions (which reduced light pollution), to resolve stars in the center of the Andromeda Galaxy for the first time.

Book of Fixed Stars

Book of the Fixed StarsUranometry
He referred to it in his Book of Fixed Stars as a "nebulous smear".
5323).He has the earliest known descriptions and illustrations of what he called "a little cloud", which is actually the Andromeda Galaxy.

William Herschel

HerschelSir William HerschelWilliam
In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda.
Between 1783 and 1787, she made an independent discovery of M110 (NGC 205), which is the second companion of the Andromeda Galaxy.

Universe

physical worldThe Universeuniverses
In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe.
As an example, the Milky Way is roughly 100,000–180,000 light-years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light-years away.

Harlow Shapley

Shapley, HarlowH. ShapleyShapley
In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe.
The astronomical issues were soon resolved in favor of Curtis' position when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy.

Parsec

Mpcpckpc
The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula (see below), is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way.

Great Debate (astronomy)

Great DebateShapley-Curtis DebateShapley–Curtis debate
In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the Universe.
He believed that "spiral nebulae" such as Andromeda were simply part of the Milky Way.

Abd al-Rahman al-Sufi

al-SufiAl SufiAzophi
Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi was the first to describe the Andromeda Galaxy.
He also made the earliest recorded observation of the Andromeda Galaxy in 964 AD; describing it as a "small cloud".

Triangulum Galaxy

M33TriangulumMessier 33
Andromeda and the Triangulum Galaxy had a very close passage 2–4 billion years ago.
The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Milky Way and the Andromeda Galaxy.

Ernst Öpik

Ernst Julius ÖpikErnst J. ÖpikE. J. Opik
In 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars.
In 1922, Ernst Öpik published a paper in which he estimated the distance of the Andromeda Galaxy.

Light-year

light yearlight yearsMly
The Andromeda Galaxy (IPA: ), also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula (see below), is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way.

Jodrell Bank Observatory

Jodrell BankTransit TelescopeNuffield Radio Astronomy Laboratories
In 1950, radio emission from the Andromeda Galaxy was detected by Hanbury Brown and Cyril Hazard at Jodrell Bank Observatory.
It discovered radio noise from the Great Nebula in Andromeda—the first definite detection of an extragalactic radio source—and the remains of Tycho's Supernova in the radio frequency; at the time it had not been discovered by optical astronomy.

Apparent magnitude

apparent visual magnitudemagnitudevisual magnitude
With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects making it visible to the naked eye from Earth on moonless nights, even when viewed from areas with moderate light pollution.

Nova

recurrent novaclassical novanovae
At the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly; "Nova 1885".
Roughly 25 novae brighter than about the twentieth magnitude are discovered in the Andromeda Galaxy each year and smaller numbers are seen in other nearby galaxies.

Mount Wilson Observatory

Hooker TelescopeMount WilsonMt. Wilson Observatory
These were made using the 2.5 m Hooker telescope, and they enabled the distance of Great Andromeda Nebula to be determined.