Editing Andromeda (constellation) (section)

== Features ==

=== Stars ===
{{Further|List of stars in Andromeda}}
[[File:Andromeda annotated.png|thumb|400px|Andromeda as it appears in the night sky, with the superimposed figure.]]
* [[Alpha Andromedae|α And]] (Alpheratz) is the brightest [[star]] in this constellation. It is an [[Ap and Bp stars|A0p class]]{{sfn|Moore|Tirion|1997|pp=116–117}} binary star with an overall [[apparent visual magnitude]] of 2.1 and a [[luminosity]] of {{Solar luminosity|link=y|96}}.{{sfn|Moore|2000|pp=328–330}} It is 97 [[light-year]]s from Earth.{{sfn|SIMBAD Alpha And}} In Western mythology it represents Andromeda's head, although the star's traditional [[Arabic]] names, Alpheratz and Sirrah, come from the phrase ''surrat al-faras'', referring to the navel of the horse.<ref>{{cite web|url=http://www.ianridpath.com/startales/andromeda.html#stars |author=Ian Ridpath |author-link=Ian Ridpath |title=Star Tales – Andromeda|access-date=31 January 2025}}</ref>{{sfn|Odeh|Kunitzsch|1998}} The Arabic names are a reference to the fact that α And forms an [[asterism (astronomy)|asterism]] known as the Great Square of Pegasus with three stars in [[Pegasus (constellation)|Pegasus]]: [[Alpha Pegasi|α]], [[Beta Pegasi|β]], and [[Gamma Pegasi|γ Peg]]. As such, the star was formerly considered to belong to both Andromeda and Pegasus, and was co-designated Delta Pegasi (δ Peg), although this name is no longer formally used.{{sfn|Moore|Tirion|1997|pp=116–117}}{{sfn|Ridpath, ''Star Tales'' Andromeda}}{{sfn|Moore|2000|pp=328–330}}
* [[Beta Andromedae|β And]] (Mirach) is a red-hued giant star of [[M-type star|type M0]]{{sfn|Moore|Tirion|1997|pp=116–117}}{{sfn|SIMBAD Mirach}} located in an asterism known as the "girdle". It is 198 light-years away,{{sfn|SIMBAD Mirach}} has a magnitude of 2.06,{{sfn|Ridpath|2001|pp=72–74}} and a luminosity of {{Solar luminosity|115}} with a planet discovered orbiting this star ([[Beta Andromedae b|b]]).{{sfn|Moore|2000|pp=328–330}} Its name comes from the Arabic phrase ''al-Maraqq'' meaning "the loins" or "the loincloth",{{sfn|Odeh|Kunitzsch|1998}} a phrase translated from Ptolemy's writing. However, β And was mostly considered by the Arabs to be a part of al-Hut, a constellation representing a larger fish than Pisces at Andromeda's feet.{{sfn|Davis|1944}}
* [[Gamma Andromedae|γ And]] (Almach) is an orange-hued bright giant star of [[K-type star|type K3]]{{sfn|Moore|Tirion|1997|pp=116–117}} found at the southern tip of the constellation with an overall magnitude of 2.14.{{sfn|Moore|2000|pp=328–330}} Almach is a [[multiple star]] with a yellow primary of magnitude 2.3 and a blue-green secondary of magnitude 5, separated by 9.7 [[arcsecond]]s.{{sfn|Thompson|Thompson|2007|pp=66–73}}{{sfn|Ridpath, ''Star Tales'' Andromeda}}{{sfn|Ridpath|Tirion|2009|pp=61–62}} British astronomer William Herschel said of the star: "[the] striking difference in the color of the 2 stars, suggests the idea of a sun and its planet, to which the contrast of their unequal size contributes not a little."{{sfn|French|2006}} The secondary, described by Herschel as a "fine light sky-blue, inclining to green",{{sfn|French|2006}} is itself a double star, with a secondary of magnitude 6.3{{sfn|Thompson|Thompson|2007|pp=66–73}} and a period of 61 years.{{sfn|Moore|2000|pp=328–330}} The system is 358 light-years away.{{sfn|SIMBAD Gamma1 Andromedae}} Almach was named for the Arabic phrase ''ʿAnaq al-Ard'', which means "the earth-kid", an obtuse reference to an animal that aids a lion in finding prey.{{sfn|Davis|1944}}{{sfn|Odeh|Kunitzsch|1998}}
* [[Delta Andromedae|δ And]] is an orange-hued giant star of [[K-type star|type K3]]{{sfn|Moore|Tirion|1997|pp=116–117}} [[orange giant]] of magnitude 3.3.{{sfn|Ridpath|2001|pp=72–74}} It is 105 light-years from Earth.{{sfn|SIMBAD Delta Andromedae}}
* [[Iota Andromedae|ι And]], [[Kappa Andromedae|κ]], [[Lambda Andromedae|λ]], [[Omicron Andromedae|ο]], and [[Psi Andromedae|ψ And]] form an asterism known as "Frederick's Glory", a name derived from a [[Former constellations|former constellation]] ([[Frederici Honores]]).{{sfn|Bakich|1995|p=43}} ι And is a blue-white hued main-sequence star of [[B-type star|type B8]], 502 light-years from Earth;{{sfn|SIMBAD Iota And}} κ And is a white-hued main-sequence star of type B9 IVn, 168 light-years from Earth;{{sfn|SIMBAD Kappa Andromedae}} λ And is a yellow-hued giant star of type G8, 86 light-years from Earth;{{sfn|SIMBAD Lambda Andromedae}} ο And is a blue-white hued giant star of type B6, 679 light-years from Earth;{{sfn|SIMBAD Omicron Andromedae}} and ψ And is a blue-white hued main-sequence star of type B7, 988 light-years from Earth.{{sfn|SIMBAD Psi Andromedae}}
* [[Mu Andromedae|μ And]] is a white-hued main-sequence star of type A5 and magnitude 3.9.{{sfn|Ridpath|2001|pp=72–74}} It is 130 light-years away.{{sfn|SIMBAD 37 Andromedae}}
* [[Upsilon Andromedae|υ And]] (Titawin)<ref name="IAU-LSN"/> is a magnitude 4.1{{sfn|Ridpath|2001|pp=72–74}} binary system that consists of one [[F-type dwarf]] and an [[M-type dwarf]]. The primary star has a [[planetary system]] with 4 confirmed [[extrasolar planet|planets]],<ref name=Ligi2012>{{cite journal |display-authors=1 | first1=R. | last1=Ligi | first2=D. | last2=Mourard | first3=A. M. | last3=Lagrange | first4=K. | last4=Perraut | first5=T. | last5=Boyajian | first6=Ph. | last6=Bério | first7=N. | last7=Nardetto | first8=I. | last8=Tallon-Bosc | first9=H. | last9=McAlister | first10=T. | last10=ten Brummelaar | first11=S. | last11=Ridgway | first12=J. | last12=Sturmann | first13=L. | last13=Sturmann | first14=N. | last14=Turner | first15=C. | last15=Farrington | first16=P. J. | last16=Goldfinger |title=A new interferometric study of four exoplanet host stars : θ Cygni, 14 Andromedae, υ Andromedae and 42 Draconis |journal=Astronomy & Astrophysics |volume=545 |pages=A5 | date=2012 |doi=10.1051/0004-6361/201219467 |bibcode=2012A&A...545A...5L |arxiv = 1208.3895 | s2cid=10934982 }}</ref> 0.96 times, 14.57 times, 10.19 times and 1.06 the mass of [[Jupiter]].{{sfn|''ExoPlanet'' ups And}} The system is 44 light-years from Earth.{{sfn|SIMBAD Ups And}}
* [[Xi Andromedae|ξ And]] (Adhil) is a binary star 217 light-years away. The primary is an orange-hued giant star of type K0.{{sfn|SIMBAD Xi Andromedae}}
* [[Pi Andromedae|π And]] is a blue-white hued binary star of magnitude 4.3{{sfn|Ridpath|2001|pp=72–74}} that is 598 light-years away. The primary is a main-sequence star of type B5.{{sfn|SIMBAD 29 And}} Its companion star is of magnitude 8.9.{{sfn|Ridpath|2001|pp=72–74}}
* [[51 Andromedae|51 And]] (Nembus<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=30 July 2018}}</ref>) was assigned by [[Johann Bayer]] to Perseus, where he designated it "Upsilon Persei (υ Per)", but it was moved to Andromeda by the International Astronomical Union.{{sfn|Wagman|2003|p=240}} It is 177 light-years from Earth and is an orange-hued giant star of type K3.{{sfn|SIMBAD 51 And}}
* 54 And was a former designation for [[Phi Persei|φ Per]].{{sfn|Ridpath, ''Star Tales'' Andromeda}}{{sfn|Wagman|2003|p=240}}
* [[56 Andromedae|56 And]] is an optical binary star. The primary is a yellow-hued giant star of type K0 with an apparent magnitude of 5.7{{sfn|Ridpath|2001|pp=72–74}} that is 316 light-years away.{{sfn|SIMBAD 56 And}} The secondary is an orange-hued giant star of type K0 and magnitude 5.9 that is 990 light-years from Earth.{{sfn|Ridpath|2001|pp=72–74}}
* [[R Andromedae|R And]] is a [[Mira variable|Mira-type variable star]] with a period of 409 days. Its maximum magnitude is 5.8 and its minimum magnitude is 14.8,{{sfn|Moore|Tirion|1997|pp=116–117}} and it is at a distance of 1,250 light-years.{{sfn|SIMBAD R And}} There are 6 other Mira variables in Andromeda.{{sfn|Moore|2000|pp=328–330}}
* [[Z Andromedae|Z And]] is the M-type prototype for [[Z Andromedae variable|its class]] of variable stars. It ranges in magnitude from a minimum of 12.4 to a maximum of 8.{{sfn|Moore|2000|pp=328–330}} It is 2,720 light-years away.{{sfn|SIMBAD Z And}}
* [[Ross 248]] (HH Andromedae)  is the ninth-closest star to Earth at a distance of 10.3 light-years.{{sfn|RECONS, ''The 100 Nearest Star Systems''}} It is a red-hued main-sequence [[BY Draconis variable star]] of type M6.{{sfn|SIMBAD HH And}}
* [[14 Andromedae|14 And]] (Veritate<ref name="IAU-LSN"/>) is a yellow-hued giant star of type G8 that is 251 light-years away.{{sfn|SIMBAD 14 And}} It has a mass of {{Solar mass|link=y|2.2}} and a radius of {{Solar radius|link=y|11}}. It has one planet, [[14 Andromedae b]], discovered in 2008. It orbits at a distance of 0.83 [[astronomical units]] from its parent star every 186 days and has a mass of {{Jupiter mass|link=y|4.3}}.{{sfn|''ExoPlanet'' Planet 14 And b}}

[[File:Andromeda H-R.png|alt=A Hertzsprung-Russel diagram for stars above 4th magnitude in the Andromeda constellation (axes not labelled).|thumb|250x250px|A [[Hertzsprung–Russell diagram]] for stars brighter than 4th [[Apparent magnitude|magnitude]] in the constellation Andromeda (axes not labelled).]]
Of the stars brighter than 4th [[Apparent magnitude|magnitude]] (and those with measured [[luminosity]]), Andromeda has a relatively even distribution of [[Stellar evolution|evolved]] and [[Main sequence|main-sequence]] stars.

=== Deep-sky objects ===
[[File:M31bobo.jpg|thumb|250px|right|M31, the Great Galaxy of Andromeda.]]

Andromeda's borders contain many visible distant galaxies.{{sfn|Thompson|Thompson|2007|pp=66–73}} The most famous [[deep-sky object]] in Andromeda is the [[spiral galaxy]] cataloged as Messier 31 (M31) or NGC 224 but known colloquially as the [[Andromeda Galaxy]]  for the constellation.{{sfn|Pasachoff|2000|p=244}} M31 is one of the most distant objects visible to the naked eye, 2.2&nbsp;million light-years from Earth (estimates range up to 2.5 million light-years).{{sfn|Wilkins|Dunn|2006|pp=348, 366}}  It is seen under a dark, transparent sky as a hazy patch in the north of the constellation.{{sfn|Wilkins|Dunn|2006|pp=348, 366}} M31 is the largest neighboring galaxy to the Milky Way and the largest member of the [[Local Group]] of galaxies.{{sfn|Pasachoff|2000|p=244}}{{sfn|Wilkins|Dunn|2006|pp=348, 366}} In absolute terms, M31 is approximately 200,000 light-years in diameter, twice the size of the Milky Way.{{sfn|Wilkins|Dunn|2006|pp=348, 366}} It is an enormous&nbsp;– 192.4 by 62.2 arcminutes in [[apparent size]]{{sfn|Thompson|Thompson|2007|pp=66–73}}&nbsp;– [[barred spiral galaxy]] similar in form to the Milky Way and at an approximate magnitude of 3.5, is one of the brightest deep-sky objects in the northern sky.{{sfn|Bakich|1995|p=51}} Despite being visible to the naked eye, the "little cloud" near Andromeda's figure was not recorded until AD 964, when the Arab astronomer [[al-Sufi]] wrote his ''[[Book of Fixed Stars]]''.{{sfn|Ridpath, ''Star Tales'' Andromeda}}{{sfn|Higgins|2002}} M31 was first observed telescopically shortly after its invention, by [[Simon Marius]] in 1612.{{sfn|Rao|2011}}

The future of the Andromeda and Milky Way galaxies may be interlinked: in about five billion years, the two could potentially begin an [[Andromeda–Milky Way collision]] that would spark extensive new star formation.{{sfn|Wilkins|Dunn|2006|pp=348, 366}}

[[File:Andromeda Galaxy M31 - Heic1502a Full resolution.jpg|thumbnail|250px|left|''[[Zooming In on the Andromeda Galaxy]] –'' A mosaic of the Andromeda Galaxy and the largest images ever taken using the [[Hubble Space Telescope]]<ref>{{cite web|title=Sharpest ever view of the Andromeda Galaxy|url=http://www.spacetelescope.org/images/heic1502a/|website=www.spacetelescope.org|publisher=ESA/Hubble|access-date=14 January 2015}}</ref>]]

American astronomer [[Edwin Hubble]] included M31 (then known as the Andromeda Nebula) in his groundbreaking 1923 research on galaxies.{{sfn|Higgins|2002}} Using the 100-inch [[Hooker Telescope]] at [[Mount Wilson Observatory]] in California, he observed [[Cepheid variable]] stars in M31 during a search for [[nova]]e, allowing him to determine their distance by using the stars as [[standard candle]]s.{{sfn|Hoskin|Dewhirst|1999|pp=292–296}} The distance he found was far greater than the size of the Milky Way, which led him to the conclusion that many similar objects were "island universes" on their own.{{sfn|ESA, ''Edwin Powell Hubble''}}{{sfn|PBS, ''Edwin Hubble''|1998}}{{sfn|HubbleSite, ''About Edwin Hubble''|2008}} Hubble originally estimated that the Andromeda Galaxy was 900,000 light-years away, but [[Ernst Öpik]]'s estimate in 1925 put the distance closer to 1.5 million light-years.{{sfn|Hoskin|Dewhirst|1999|pp=292–296}}

The Andromeda Galaxy's two main companions, [[Messier 32|M32]] and [[Messier 110|M110]] (also known as NGC 221 and NGC 205, respectively) are faint elliptical galaxies that lie near it.{{sfn|Bakich|1995|p=54}}{{sfn|Pasachoff|2000|p=244}} M32, visible with a far smaller size of 8.7 by 6.4 arcminutes,{{sfn|Thompson|Thompson|2007|pp=66–73}} compared to M110, appears superimposed on the larger galaxy in a telescopic view as a hazy smudge, M110 also appears slightly larger and distinct from the larger galaxy;{{sfn|Pasachoff|2000|p=244}} M32 is 0.5° south of the core, M110 is 1° northwest of the core.{{sfn|Ridpath|2001|pp=72–74}} M32 was discovered in 1749 by French astronomer [[Guillaume Le Gentil]] and has since been found to lie closer to Earth than the Andromeda Galaxy itself.{{sfn|Block|2003}} It is viewable in binoculars from a dark site owing to its high surface brightness of 10.1 and overall magnitude of 9.0.{{sfn|Thompson|Thompson|2007|pp=66–73}} M110 is classified as either a [[dwarf spheroidal galaxy]] or simply a generic elliptical galaxy. It is far fainter than M31 and M32, but larger than M32 with a surface brightness of 13.2, magnitude of 8.9, and size of 21.9 by 10.9 arcminutes.{{sfn|Thompson|Thompson|2007|pp=66–73}}

The Andromeda Galaxy has a total of 15 [[List of Andromeda's satellite galaxies|satellite galaxies]], including M32 and M110. Nine of these lie in a plane, which has caused astronomers to infer that they have a common origin. These satellite galaxies, like the [[List of Milky Way's satellite galaxies|satellites of the Milky Way]], tend to be older, gas-poor [[dwarf elliptical galaxy|dwarf elliptical]] and [[dwarf spheroidal galaxy|dwarf spheroidal galaxies]].{{sfn|Koch|Grebel|2006}}

[[File:NGC 7662 Hubble WikiSky.jpg|thumb|250px|left|The Blue Snowball Nebula as seen through the [[Hubble Space Telescope]].]]

Along with the Andromeda Galaxy and its companions, the constellation also features [[NGC 891]] (Caldwell 23), a smaller galaxy just east of [[gamma Andromedae|Almach]]. It is a barred spiral galaxy seen edge-on, with a dark [[dust lane]] visible down the middle. NGC 891 is incredibly faint and small despite its magnitude of 9.9,{{sfn|Moore|2000|pp=328–330}} as its surface brightness of 14.6 indicates;{{sfn|Thompson|Thompson|2007|pp=66–73}} it is 13.5 by 2.8 arcminutes in size.{{sfn|Moore|2000|pp=328–330}} NGC 891 was discovered by the brother-and-sister team of [[William Herschel|William]] and [[Caroline Herschel]] in August 1783.{{sfn|Wilkins|Dunn|2006|pp=348, 366}} This galaxy is at an approximate distance of 30 million light-years from Earth, calculated from its [[redshift]] of 0.002.{{sfn|Wilkins|Dunn|2006|pp=348, 366}}

Andromeda's most celebrated [[open cluster]] is [[NGC 752]] ([[Caldwell Catalogue|Caldwell]] 28) at an overall magnitude of 5.7.{{sfn|Moore|2000|pp=328–330}} It is a loosely scattered cluster in the Milky Way that measures 49 arcminutes across and features approximately twelve bright stars, although more than 60 stars of approximately 9th magnitude become visible at low magnifications in a telescope.{{sfn|Thompson|Thompson|2007|pp=66–73}}{{sfn|Ridpath|2001|pp=72–74}} It is considered to be one of the more inconspicuous open clusters.{{sfn|Moore|Tirion|1997|pp=116–117}} The other open cluster in Andromeda is [[NGC 7686]], which has a similar magnitude of 5.6 and is also a part of the Milky Way. It contains approximately 20 stars in a diameter of 15 arcminutes, making it a tighter cluster than NGC 752.{{sfn|Moore|2000|pp=328–330}}

There is one prominent [[planetary nebula]] in Andromeda: [[NGC 7662]] (Caldwell 22).{{sfn|Moore|2000|pp=328–330}} Lying approximately 3 degrees southwest of [[Iota Andromedae]] at a distance of about 4,000 light-years from Earth, the "Blue Snowball Nebula"{{sfn|Thompson|Thompson|2007|pp=66–73}} is a popular target for amateur astronomers.{{sfn|Pasachoff|2000|p=270}} It earned its popular name because it appears as a faint, round, blue-green object in a telescope, with an overall magnitude of 9.2.{{sfn|Thompson|Thompson|2007|pp=66–73}}{{sfn|Pasachoff|2000|p=270}} Upon further magnification, it is visible as a slightly elliptical annular disk that gets darker towards the center, with a magnitude 13.2 central star.{{sfn|Thompson|Thompson|2007|pp=66–73}}{{sfn|Ridpath|2001|pp=72–74}} The nebula has an overall magnitude of 9.2 and is 20 by 130 arcseconds in size.{{sfn|Moore|2000|pp=328–330}}

=== Meteor showers ===
Each November, the [[Andromedids]] meteor shower appears to radiate from Andromeda.{{sfn|Bakich|1995|p=60}} The shower peaks in mid-to-late November every year, but has a low peak rate of fewer than 2 meteors per hour.{{sfn|Lunsford, ''Meteor Shower List''|2012}} Astronomers have often associated the Andromedids with [[Biela's Comet]], which was destroyed in the 19th century, but that connection is disputed.{{sfn|Jenniskens|2008}} Andromedid meteors are known for being very slow and the shower itself is considered to be diffuse, as meteors can be seen coming from nearby constellations as well as from Andromeda itself.{{sfn|Lunsford, ''Activity Nov 19–23''|2011}} Andromedid meteors sometimes appear as red [[Meteoroid#Fireball|fireballs]].{{sfn|Sherrod|Koed|2003|p=58}}{{sfn|Jenniskens|Vaubaillon|2007}} The Andromedids were associated with the most spectacular meteor showers of the 19th century; the storms of 1872 and 1885 were estimated to have a peak rate of 2 meteors per second (a [[zenithal hourly rate]] of 10,000), prompting a Chinese astronomer to compare the meteors to falling rain.{{sfn|Jenniskens|2008}}{{sfn|Jenniskens|2006|p=384}} The Andromedids had another outburst on December 3–5, 2011, the most active shower since 1885, with a maximum zenithal hourly rate of 50 meteors per hour. The 2011 outburst was linked to ejecta from Comet Biela, which passed close to the Sun in 1649. None of the meteoroids observed were associated with material from the comet's 1846 disintegration. The observers of the 2011 outburst predicted outbursts in 2018, 2023, and 2036.{{sfn|Wiegert|Brown|Weryk|Wong|2012}}
{{clear}}