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{{Short description|Constellation in the northern celestial hemisphere}}
{{Infobox constellation
| name = Pegasus
| abbreviation = Peg
| genitive = Pegasi
| pronounce = {{IPAc-en|ˈ|p|ɛ|ɡ|ə|s|ə|s}},<br/>genitive {{IPAc-en|ˈ|p|ɛ|ɡ|ə|s|aɪ}}
| symbolism = the [[Wing]]ed [[Horse]]
| RA = {{RA|21|12.6}} to {{RA|00|14.6}}<ref name=boundary/>
| dec= +2.33° to +36.61°<ref name=boundary/>
| family = [[Perseus Family|Perseus]]
| quadrant = NQ4
| areatotal = 1121
| arearank = 7th
| numbermainstars = 9, 17
| numberbfstars = 88
| numberstarsplanets = 12
| numberbrightstars = 5
| numbernearbystars = 3
| brighteststarname = [[Epsilon Pegasi|ε Peg]] (Enif)
| starmagnitude = 2.38
| neareststarname = [[EQ Pegasi|EQ Peg]]
| stardistancely = 20.38
| stardistancepc = 6.25
| numbermessierobjects = 1
| meteorshowers = July Pegasids
| bordering = [[Andromeda (constellation)|Andromeda]]<br />[[Lacerta]]<br />[[Cygnus (constellation)|Cygnus]]<br />[[Vulpecula]]<br />[[Delphinus]]<br />[[Equuleus]]<br />[[Aquarius (constellation)|Aquarius]]<br />[[Pisces (constellation)|Pisces]]
| latmax = [[North Pole|90]]
| latmin = [[60th parallel south|60]]
| month = October
| notes=}}
'''Pegasus''' is a [[constellation]] in the northern sky, named after the winged horse [[Pegasus]] in [[Greek mythology]]. It was one of the 48 constellations listed by the 2nd-century [[astronomer]] [[Ptolemy]], and is one of the [[IAU designated constellations|88 constellations]] recognised today.
With an [[apparent magnitude]] varying between 2.37 and 2.45, the brightest star in Pegasus is the orange supergiant [[Epsilon Pegasi]], also known as Enif, which marks the horse's muzzle. [[Alpha Pegasi|Alpha]] (Markab), [[Beta Pegasi|Beta]] (Scheat), and [[Gamma Pegasi|Gamma]] (Algenib), together with [[Alpha Andromedae]] (Alpheratz) form the large [[Asterism (astronomy)|asterism]] known as the ''Square of Pegasus''. Twelve star systems have been found to have exoplanets. [[51 Pegasi]] was the first Sun-like star discovered to have an exoplanet companion.
==Mythology==
The Babylonian constellation IKU (field) had four stars of which three were later part of the Greek constellation ''Hippos'' (Pegasus).<ref>{{cite book|last=Thurston|first=Hugh|title=Early Astronomy|date=1996|publisher=Springer|isbn=978-0-387-94822-5|page=3}}</ref> Pegasus, in Greek mythology, was a winged horse with magical powers. One myth regarding his powers says that his hooves dug out a spring, [[Hippocrene]], which blessed those who drank its water with the ability to write poetry. Pegasus was born when [[Perseus]] cut off the head of [[Medusa]], who was impregnated by the god [[Poseidon]]. He was born with [[Chrysaor]] from Medusa's blood.<ref>{{cite book |last1=Ovid |editor1-last=Melville |editor1-first=A.D. |title=Metamorphoses |date=1986 |publisher=Oxford University Press |___location=Oxford |isbn=0-19-283472-X |page=98}}</ref> Eventually, it became the horse for [[Bellerophon]], who was asked to kill the [[Chimera (mythology)|Chimera]] and succeeded with the help of [[Athena]] and Pegasus. Despite this success, after the death of his children, Bellerophon asked Pegasus to take him to [[Mount Olympus]]. Though Pegasus agreed, he plummeted back to Earth after Zeus either threw a thunderbolt at him or sent a gadfly to make Pegasus buck him off.<ref name="staal">{{Harvnb|Staal|1988|pp=27–32}}</ref><ref>Conner, Nancy. The Everything Classical Mythology Book: from the Heights of Mount Olympus to the Depths of the Underworld - All You Need to Know about the Classical Myths. 2nd ed., Adams Media, 2010.</ref>
In ancient Persia, Pegasus was depicted by [[al-Sufi]] as a complete horse facing east, unlike most other uranographers, who had depicted Pegasus as half of a horse, rising out of the ocean. In al-Sufi's depiction, Pegasus's head is made up of the stars of [[Lacerta]] the lizard. Its right foreleg is represented by β Peg and its left foreleg is represented by η Peg, μ Peg, and λ Peg; its hind legs are marked by 9 Peg. The back is represented by π Peg and μ Cyg, and the belly is represented by ι Peg and κ Peg.<ref name="staal"/>
In [[Chinese astronomy]], the modern constellation of Pegasus lies in [[Black Tortoise|The Black Tortoise of the north]] (北方玄武), where the stars were classified in several separate [[Asterism (astronomy)|asterism]]s of stars.<ref name="ridpathcc">{{cite web| url=http://www.ianridpath.com/startales/chinese.html#lunar |work=Star Tales | title=Charting the Chinese sky |last1=Ridpath|first1=Ian|publisher=self-published | access-date= 21 May 2014}}</ref> Epsilon and Theta Pegasi are joined with [[Alpha Aquarii]] to form ''Wei'' 危 "rooftop", with Theta forming the roof apex.{{sfn|Schlegel|1967|pp=233-34}}
In Hindu astronomy, Pegasus is contained within the 25th nakshatra [[lunar mansion]] Purva Bhadrapada. More specifically, it represented a bedstead that was a resting place for the Moon.<ref name="staal"/>
For the [[Warrau]] and [[Arawak]] peoples in [[Guyana]] the stars in the Great Square, corresponding to parts of Pegasus and of Andromeda, represented a barbecue, taken up to the sky by the seven hunters of the myth of Siritjo.<ref name="staal"/><ref>{{Cite journal|last1=Magaña |first1=Edmundo |last2=Jara|first2= Fabiola|title=The Carib sky|journal=Journal de la Société des Américanistes|volume=68|issue=1|page=114|year=1982|doi=10.3406/jsa.1982.2212 |url=http://www.persee.fr/doc/jsa_0037-9174_1982_num_68_1_2212}}</ref>
==Characteristics==
Covering 1121 square degrees, Pegasus is the seventh-largest of the 88 constellations. Pegasus is bordered by Andromeda to the north and east, [[Lacerta]] to the north, [[Cygnus (constellation)|Cygnus]] to the northwest, [[Vulpecula]], [[Delphinus]] and [[Equuleus]] to the west, [[Aquarius (constellation)|Aquarius]] to the south and [[Pisces (constellation)|Pisces]] to the south and east. The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Peg".<ref name=pa30_469>{{cite journal | last=Russell | first=Henry Norris |author-link=Henry Norris Russell | title=The New International Symbols for the Constellations | journal=Popular Astronomy | volume=30 | page=469 | bibcode=1922PA.....30..469R | date=1922 }}</ref> The official constellation boundaries, as set by Belgian astronomer [[Eugène Joseph Delporte|Eugène Delporte]] in 1930, are defined as a polygon of 35 segments. In the [[equatorial coordinate system]] the [[right ascension]] coordinates of these borders lie between {{RA|21|12.6}} and {{RA|00|14.6}}, while the [[declination]] coordinates are between 2.33° and 36.61°.<ref name=boundary>{{Cite journal | title=Pegasus, Constellation Boundary | journal=The Constellations | publisher=International Astronomical Union | url=https://www.iau.org/public/themes/constellations/#peg | access-date=13 February 2014}}</ref> Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 53°S.<ref name=tirionconst>{{cite web| url=http://www.ianridpath.com/constellations2.html | title=Constellations: Lacerta–Vulpecula | work= Star Tales |author=Ian Ridpath |author-link=Ian Ridpath|publisher=self-published | access-date= 29 November 2014}}</ref>{{efn|1=While parts of the constellation technically rise above the horizon to observers between the 53°S and 87°S, stars within a few degrees of the horizon are to all intents and purposes unobservable.<ref name=tirionconst/>}}
[[File:Sidney Hall - Urania's Mirror - Pegasus and Equuleus (best currently available version - 2014).jpg|thumb|300px|Pegasus with the foal [[Equuleus]] next to it, as depicted in ''[[Urania's Mirror]]'', a set of constellation cards published in London c.1825. The horses appear upside-down in relation to the constellations around them.]]
Pegasus is dominated by a roughly square asterism (the Square of Pegasus) although one of the stars, formerly known as Delta Pegasi or Sirrah, is now officially assigned to [[Andromeda (constellation)|Andromeda]] and is known as [[Alpha Andromedae]], or Alpheratz.<ref>{{cite web|url=http://www.ianridpath.com/startales/pegasus.html#stars |author=Ian Ridpath |author-link=Ian Ridpath |title=Star Tales – Pegasus|access-date=31 January 2025}}</ref> Traditionally, the body of the horse consists of a quadrilateral formed by the stars [[Alpha Pegasi|α Peg]], [[Beta Pegasi|β Peg]], [[Gamma Pegasi|γ Peg]], and [[Alpha Andromedae|α And]]. The front legs of the winged horse are formed by two crooked lines of stars, one leading from [[Eta Pegasi|η Peg]] to [[Kappa Pegasi|κ Peg]] and the other from [[Mu Pegasi|μ Peg]] to [[1 Pegasi]]. Another crooked line of stars from [[Alpha Pegasi|α Peg]] via [[Theta Pegasi|θ Peg]] to [[Epsilon Pegasi|ε Peg]] forms the neck and head; ε is the snout.
==Features==
[[Image:PegasusCC.jpg|thumb|300px|The constellation Pegasus as it can be seen by the naked eye]]
===Stars===
{{See also|List of stars in Pegasus}}
Bayer catalogued what he counted as 23 stars in the constellation, giving them the [[Bayer designation]]s Alpha to Psi. He saw [[Pi Pegasi]] as one star, and was uncertain of its brightness, wavering between magnitude 4 and 5. Flamsteed labelled this star 29 Pegasi, but Bode concluded that the stars 27 and 29 Pegasi should be [[Pi1 Pegasi|Pi<sup>1</sup>]] and [[Pi2 Pegasi|Pi<sup>2</sup> Pegasi]] and that Bayer had seen them as a single star.{{sfn|Wagman|2003|p=235}} Flamsteed added lower case letters e through to y, omitting A to D as they had been used on Bayer's chart to designate neighbouring constellations and the equator.{{sfn|Wagman|2003|p=236}} He numbered 89 stars (now with Flamsteed designations), though 6 and 11 turned out to be stars in Aquarius.{{sfn|Wagman|2003|p=448}} Within the constellation's borders there are 177 stars of [[apparent magnitude]] 6.5 or greater.{{efn|1=Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.<ref>{{cite web|url=http://www.skyandtelescope.com/resources/darksky/3304011.html?page=1&c=y|title=The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=February 2001|work=[[Sky & Telescope]]|publisher=Sky Publishing Corporation|access-date=29 November 2014}}</ref>}}<ref name=tirionconst/>
[[Epsilon Pegasi]], also known as Enif, marks the horse's muzzle. The brightest star in Pegasus, is an orange [[supergiant]] of [[Stellar classification#Spectral types|spectral type]] K21b that is around 12 times [[solar mass|as massive as the Sun]] and is around 690 [[light-year]]s distant from Earth.<ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=eps+peg&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Epsilon Pegasi -- Pulsating Variable Star |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 12 February 2014}}</ref> It is an irregular variable, its [[apparent magnitude]] varying between 2.37 and 2.45.<ref name=AAVSOeps>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=25522 |title=Epsilon Pegasi |author =Otero, Sebastian Alberto|date=7 June 2011 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=12 February 2014}}</ref> Lying near Enif is [[AG Pegasi]], an unusual star that brightened to magnitude 6.0 around 1885 before dimming to magnitude 9. It is composed of a [[red giant]] and [[white dwarf]], estimated to be around 2.5 and 0.6 times the mass of the Sun respectively. With its outburst taking over 150 years, it has been described as the slowest [[nova]] ever recorded.<ref name="kenyon93">{{cite journal|author= Kenyon, Scott J.|author2= Mikolajewska, Joanna|author3= Mikolajewski, Maciej|author4= Polidan, Ronald S.|author5= Slovak, Mark H.|title=Evolution of the symbiotic binary system AG Pegasi - The slowest classical nova eruption ever recorded|journal=Astronomical Journal|volume=106|issue=4|pages=1573–98|bibcode=1993AJ....106.1573K|date=1993|url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1993AJ....106.1573K&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf|doi = 10.1086/116749 }}</ref><!-- cites previous three sentences -->
Three stars with Bayer designations that lie within the Great Square are variable stars. [[Phi Pegasi|Phi]] and [[Psi Pegasi]] are pulsating red giants, while [[Tau Pegasi]] (the proper name is Salm<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=8 August 2018}}</ref>), is a [[Delta Scuti variable]]—a class of short period (six hours at most) pulsating stars that have been used as [[Cosmic distance ladder#Standard candles|standard candles]] and as subjects to study [[astroseismology]].<ref>{{cite web|url=http://www.aavso.org/vsots_delsct|title=Delta Scuti and the Delta Scuti Variables|last=Templeton|first=Matthew |date=16 July 2010|work=Variable Star of the Season|publisher=AAVSO (American Association of Variable Star Observers)|access-date=16 March 2016}}</ref> Rotating rapidly with a [[projected rotational velocity]] of 150 km s<sup>−1</sup>, Kerb is almost 30 times as luminous as the Sun and has a pulsation period of 56.5 minutes. With an outer atmosphere at an [[effective temperature]] of 7,762 K, it is a white star with a spectral type of A5IV.<ref name=mnras309_1_221>{{cite journal | last1=Balona | first1=L. A. | last2=Dziembowski | first2=W. A. | title=Excitation and visibility of high-degree modes in stars | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=309 | issue=1 | pages=221–32 |date=1999 | doi=10.1046/j.1365-8711.1999.02821.x | bibcode=1999MNRAS.309..221B | doi-access=free }}</ref>
[[Zeta Pegasi|Zeta]], [[Xi Pegasi|Xi]], [[Rho Pegasi|Rho]] and [[Sigma Pegasi]] mark the horse's neck.{{sfn|Wagman|2003|p=513}} The brightest of these with a magnitude of 3.4 is Zeta, also traditionally known as Homam. Lying seven degrees southwest of Markab, it is a blue-white main sequence star of spectral type B8V located around 209 light-years distant.<ref name=Kalerzeta>{{cite web | url=http://stars.astro.illinois.edu/sow/homam.html | title=Homam (Zeta Pegasi) | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois |date = 16 November 2007 | access-date=13 February 2014}}</ref> It is a [[slowly pulsating B star]] that varies slightly in luminosity with a period of 22.952 ± 0.804 hours, completing 1.04566 cycles per day.<ref name=pasp119_855_483>{{cite journal| last1=Goebel | first1=John H. | title=Gravity Probe B Photometry and Observations of ζ Pegasi: An SPB Variable Star | journal=The Publications of the Astronomical Society of the Pacific | volume=119 | issue=855 | pages=483–93 |date=2007 | doi=10.1086/518618 | bibcode=2007PASP..119..483G | doi-access=free }}</ref> Xi lies 2 degrees northeast, and is a [[F-type main sequence star|yellow-white main sequence star]] of spectral type F6V that is 86% larger and 17% more massive that the Sun, and radiate 4.5 times the [[solar luminosity]].<ref name=apj720_2_1290>{{cite journal | last1=Ghezzi | first1=L. | last2=Cunha | first2=K. | last3=Smith | first3=V. V. | last4=de Araújo | first4=F. X. | last5=Schuler | first5=S. C. | last6=de la Reza | first6=R. | title=Stellar Parameters and Metallicities of Stars Hosting Jovian and Neptunian Mass Planets: A Possible Dependence of Planetary Mass on Metallicity | journal=The Astrophysical Journal | volume=720 | issue=2 | pages=1290–1302 | date=2010 | doi=10.1088/0004-637X/720/2/1290 | bibcode=2010ApJ...720.1290G|arxiv = 1007.2681 | s2cid=118565025 }}</ref> It has a red dwarf companion that is 192.3 au distant.<ref name=apj801_2_143>{{cite journal | last1=Moro-Martín | first1=A. | last2=Marshall | first2=J. P. | last3=Kennedy | first3=G. | last4=Sibthorpe | first4=B. | last5=Matthews | first5=B. C. | last6=Eiroa | first6=C. | last7=Wyatt | first7=M. C. | last8=Lestrade | first8=J.-F. | last9=Maldonado | first9=J. | last10=Rodriguez | first10=D. | last11=Greaves | first11=J. S. | last12=Montesinos | first12=B. | last13=Mora | first13=A. | last14=Booth | first14=M. | last15=Duchêne | first15=G. | last16=Wilner | first16=D. | last17=Horner | first17=J. | title=Does the Presence of Planets Affect the Frequency and Properties of Extrasolar Kuiper Belts? Results from the Herschel Debris and Dunes Surveys | journal=The Astrophysical Journal | volume=801 | issue=2 | id=143 | page=28 | date=2015 | doi=10.1088/0004-637X/801/2/143 | bibcode=2015ApJ...801..143M |arxiv = 1501.03813 | s2cid=55170390 }}</ref> If (as is likely) the smaller star is in orbit around the larger star, then it would take around 2000 years to complete a revolution.<ref name=Kalerxi>{{cite web | url=http://stars.astro.illinois.edu/sow/xipeg.html| title=Xi Pegasi | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois |date = 30 November 2007 | access-date=15 March 2016}}</ref> [[Theta Pegasi]] marks the horse's eye.{{sfn|Wagman|2003|p=513}} Also known as Biham, it is a 3.43-magnitude white main sequence star of spectral type A2V, around 1.8 times as massive, 24 times as luminous, and 2.3 times as wide as the Sun.<ref name="apj771_1_40">{{cite journal | last1=Boyajian | first1=Tabetha S. | last2=von Braun | first2=Kaspar | last3=van Belle | first3=Gerard | last4=Farrington | first4=Chris
| last5=Schaefer | first5=Gail | last6=Jones | first6=Jeremy | last7=White | first7=Russel | last8=McAlister | first8=Harold A. | last9=ten Brummelaar | first9=Theo A. | last10=Ridgway | first10=Stephen | last11=Gies | first11=Douglas | last12=Sturmann | first12=Laszlo | last13=Sturmann | first13=Judit | last14=Turner | first14=Nils H. | last15=Goldfinger | first15=P. J. | last16=Vargas | first16=Norm | title=Stellar Diameters and Temperatures. III. Main-sequence A, F, G, and K Stars: Additional High-precision Measurements and Empirical Relations | journal=The Astrophysical Journal | volume=771 | issue=1 | id=40 | page=31 | date=2013 | arxiv=1306.2974 | doi=10.1088/0004-637X/771/1/40 | bibcode=2013ApJ...771...40B | s2cid=14911430 }} See Table 3.</ref>
[[Alpha Pegasi|Alpha]] (Markab), [[Beta Pegasi|Beta]] (Scheat), and [[Gamma Pegasi|Gamma]] (Algenib), together with [[Alpha Andromedae]] (Alpheratz or Sirrah) form the large [[Asterism (astronomy)|asterism]] known as the ''Square of Pegasus''. The brightest of these, Alpheratz was also known as both Delta Pegasi and Alpha Andromedae before being placed in Andromeda in 1922 with the setting of constellation boundaries. The second brightest star is Scheat, a [[red giant]] of spectral type M2.5II-IIIe located around 196 light-years away from Earth.<ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=bet+peg&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Beta Pegasi -- Pulsating Variable Star |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 13 February 2014}}</ref> It has expanded until it is some 95 times as large, and has a total [[luminosity]] 1,500 times that of the Sun.<ref name=Kalerbeta>{{cite web | url=http://stars.astro.illinois.edu/sow/scheat.html | title=Scheat (Beta Pegasi) | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois | date=22 May 2009 | access-date=13 February 2014}}</ref> Beta Pegasi is a [[semi-regular variable]] that varies from [[apparent magnitude|magnitude]] 2.31 to 2.74 over a period of 43.3 days.<ref name=AAVSObet>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=25520 |title=Beta Pegasi |author =Watson, Christopher |date=25 August 2009 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=13 February 2014}}</ref> Markab and Algenib are blue-white stars of spectral types B9III and B2IV located 133 and 391 light-years distant respectively.<ref name=simbadalpha>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alpha+peg&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Alpha Pegasi -- Variable Star |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 13 February 2014}}</ref><ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=gamma+peg&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Gamma Pegasi -- Variable Star of Beta Cephei type |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 13 February 2014}}</ref> Appearing to have moved off the main sequence as their core hydrogen supply is being or has been exhausted, they are enlarging and cooling to eventually become red giant stars.<ref name=Kaleralpha>{{cite web | url=http://stars.astro.illinois.edu/sow/markab.html | title=Markab (Alpha Pegasi) | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois | access-date=13 February 2014}}</ref><ref name=Kalergamma>{{cite web | url=http://stars.astro.illinois.edu/sow/algenib.html | title=Algenib (Gamma Pegasi) | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois | access-date=13 February 2014}}</ref> Markab has an apparent magnitude of 2.48,<ref name=simbadalpha/> while Algenib is a [[Beta Cephei variable]] that varies between magnitudes 2.82 and 2.86 every 3 hours 38 minutes, and also exhibits some slow pulsations every 1.47 days.<ref name=AAVSOgam>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=25521 |title=Gamma Pegasi |author =Otero, Sebastian Alberto|date=26 March 2011 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=13 February 2014}}</ref>
[[Eta Pegasi|Eta]] and [[Omicron Pegasi]] mark the left knee and Pi Pegasi the left hoof, while [[Iota Pegasi|Iota]] and [[Kappa Pegasi]] mark the right knee and hoof.{{sfn|Wagman|2003|p=513}} Also known as Matar, Eta Pegasi is the fifth-brightest star in the constellation. Shining with an apparent magnitude of 2.94, it is a multiple star system composed of a yellow giant of spectral type G2 and a yellow-white main sequence star of spectral type A5V that are 3.2 and 2.0 times as massive as the Sun. The two revolve around each other every 2.24 years. Farther afield is a binary system of two G-type main sequence stars, that would take 170,000 years to orbit the main pair if they are in fact related.<ref name=Kalereta>{{cite web | url=http://stars.astro.illinois.edu/sow/matar.html | title=Matar (Eta Pegasi) | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois | access-date=14 February 2014}}</ref> Omicron Pegasi has a magnitude of 4.79. Located 300 ± 20 light-years distant from Earth,<ref name="vanLeeuwen2007">{{cite journal | first=F. | last=van Leeuwen | title=Validation of the New Hipparcos Reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–64 | date=2007 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | arxiv=0708.1752| s2cid=18759600 }}</ref> it is a white subgiant that has begun to cool, expand and brighten as it exhausts its core hydrogen fuel and moves off the main sequence.<ref name=gray2014>{{cite journal | title=Precise Rotation Rates for Five Slowly Rotating a Stars |author=Gray, David F. | journal=The Astronomical Journal |volume = 147 |issue =4 |id= 81 |page= 13 |year=2014|doi=10.1088/0004-6256/147/4/81 | bibcode=2014AJ....147...81G|s2cid=121928906 }}</ref> Pi<sup>1</sup> and Pi<sup>2</sup> Pegasi appear as an optical double to the unaided eye as they are separated by 10 arcminutes, and are not a true binary system.<ref name=Kalerpi>{{cite web | url=http://stars.astro.illinois.edu/sow/pipeg.html | title=Pi Pegasi | work=Stars | first1=James B. | last1=Kaler | publisher=University of Illinois | access-date=16 March 2016}}</ref> Located 289 ± 8 light-years distant,<ref name="vanLeeuwen2007"/> Pi<sup>1</sup> is an ageing yellow giant of spectral type G6III, 1.92 times as massive and around 200 times as luminous as the Sun.<ref name=pasj60_4_781>{{cite journal | last1=Takeda | first1=Yoichi | last2=Sato | first2=Bun'ei | last3=Murata | first3=Daisuke | title=Stellar Parameters and Elemental Abundances of Late-G Giants | journal=Publications of the Astronomical Society of Japan | volume=60 | issue=4 | pages=781–802 |date=2008 | bibcode=2008PASJ...60..781T |arxiv = 0805.2434 | doi=10.1093/pasj/60.4.781| s2cid=16258166 }}</ref> Pi<sup>2</sup> is a yellow-white subgiant that is 2.5 times as massive as the Sun and has expanded to 8 times the Sun's radius and brightened to 92 times the Sun's luminosity. It is surrounded by a circumstellar disk spinning at 145 km a second,<ref name=Kalerpi/> and is 263 ± 4 light-years distant from Earth.<ref name="vanLeeuwen2007"/>
[[IK Pegasi]] is a close binary comprising an [[A-type main-sequence star]]<ref name=Skiff2014>{{citation
| title=Catalogue of Stellar Spectral Classifications
| last=Skiff | first=B. A.
| series=VizieR On-line Data Catalog: B/mk
| journal=Lowell Observatory | date=October 2014
| bibcode=2014yCat....1.2023S | postscript=. }}</ref> and [[white dwarf]]<ref name="mnras270">{{citation | last1=Barstow | first1=M. A. | last2=Holberg | first2=J. B. | last3=Koester | first3=D. | title=Extreme Ultraviolet Spectrophotometry of HD16538 and HR:8210 Ik-Pegasi | journal=Monthly Notices of the Royal Astronomical Society | date=1994 | volume=270 | issue=3 | page=516 | bibcode=1994MNRAS.270..516B | doi = 10.1093/mnras/270.3.516 | doi-access= free}}</ref> in very close orbit; the latter a candidate for a future [[type Ia supernova]]<ref name="mnras262">{{citation | last1=Wonnacott | first1=D. | last2=Kellett | first2=B. J. | last3=Stickland | first3=D. J. | title=IK Peg - A nearby, short-period, Sirius-like system | journal=Monthly Notices of the Royal Astronomical Society | date=1993 | volume=262 | issue=2 | pages=277–284 | bibcode=1993MNRAS.262..277W | doi = 10.1093/mnras/262.2.277 | doi-access=free }}</ref> as its main star runs out of core hydrogen fuel and expands into a giant and transfers material to the smaller star.
Twelve star systems have been found to have [[exoplanet]]s. [[51 Pegasi]] was the first Sun-like star discovered to have an exoplanet companion;<ref name=nature378_6555_355>{{cite journal | last1=Mayor | first1=Michael | last2=Queloz | first2=Didier | title=A Jupiter-mass companion to a solar-type star | journal=[[Nature (journal)|Nature]] | date=1995 | volume=378 | issue=6555 | pages=355–359 | doi=10.1038/378355a0 | bibcode = 1995Natur.378..355M | s2cid=4339201 }}</ref> [[51 Pegasi b]] (unofficially named Bellerophon,<ref>[http://www.berkeley.edu/news/media/releases/96legacy/releases.96/14301.html University of California at Berkeley News Release 1996-17-01]</ref> officially named Dimidium<ref>[http://www.iau.org/news/pressreleases/detail/iau1514/ Final Results of NameExoWorlds Public Vote Released], International Astronomical Union, 15 December 2015.</ref>) is a [[hot Jupiter]] close to its star, completing an orbit every four days. Spectroscopic analysis of [[HD 209458 b]], an [[extrasolar planet]] in this constellation, has provided the first evidence of atmospheric [[water vapor]] beyond the [[Solar System]],<ref>[http://www.space.com/scienceastronomy/070410_water_exoplanet.html Water Found in Extrasolar Planet's Atmosphere] – [[Space.com]]</ref><ref>{{cite web |title=Hubble Traces Subtle Signals of Water on Hazy Worlds |url=http://www.nasa.gov/content/goddard/hubble-traces-subtle-signals-of-water-on-hazy-worlds/ |date=December 3, 2013 |publisher=[[NASA]] |access-date=December 4, 2013}}</ref><ref>{{cite journal |title=Infrared Transmission Spectroscopy of the Exoplanets HD 209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope |date=September 10, 2013 |journal=[[Astrophysical Journal]] |volume=774 |issue=2 |page=95 |doi=10.1088/0004-637X/774/2/95 |arxiv = 1302.1141 |bibcode = 2013ApJ...774...95D |display-authors=1 |last1=Deming |first1=Drake |first2=Ashlee |last3=McCullough |last2 = Mccullough|first3=Peter |last4=Burrows |first4=Adam |last5=Fortney |first5=Jonathan J. |last6=Agol |first6=Eric |last7=Dobbs-Dixon |first7=Ian |last8=Madhusudhan |first8=Nikku |last9=Crouzet |first9=Nicolas |last10=Desert |first10=Jean-Michel |last11=Gilliland |first11=Ronald L. |last12=Haynes |first12=Korey |last13=Knutson |first13=Heather A. |last14=Line |first14=Michael |last15=Magic |first15=Zazralt |last16=Mandell |first16=Avi M. |last17=Ranjan |first17=Sukrit |last18=Charbonneau |first18=David |last19=Clampin |first19=Mark |last20=Seager |first20=Sara |last21=Showman |first21=Adam P. |s2cid=10960488 |author-link2=Peter Mccullough }}</ref> while extrasolar planets orbiting the star [[HR 8799]] also in Pegasus are the first to be directly imaged.<ref name=Achenbach-2008-11-13>
{{cite news
|first=Joel |last=Achenbach
|date=13 November 2008
|title=Scientists publish first direct images of extrasolar planets
|newspaper=[[The Washington Post]]
|url=https://www.washingtonpost.com/wp-dyn/content/article/2008/11/13/AR2008111302267.html
|access-date=13 November 2008
}}
</ref><ref name=Gemini-obs-2008-11-13>
{{cite press release
|title=Gemini releases historic discovery image of planetary first family
|date=13 November 2008
|publisher=[[Gemini Observatory]]
|url=http://www.gemini.edu/node/11151
|access-date=13 November 2008
}}
</ref><ref name=Keck-obs-2008-11-13>
{{cite press release
|title=Astronomers capture first images of newly-discovered solar system
|date=13 November 2008
|publisher=[[W. M. Keck Observatory]]
|url=http://www.keckobservatory.org/article.php?id=231
|access-date=13 November 2008 |archive-url=https://web.archive.org/web/20131126160805/http://www.keckobservatory.org/article.php?id=231
|archive-date=26 November 2013
}}
</ref> [[V391 Pegasi]] is a hot subdwarf star that has been found to have a planetary companion.<ref name=silvotti2007>{{citation |bibcode=2007Natur.449..189S |title=A giant planet orbiting the 'extreme horizontal branch' star V391 Pegasi |journal=Nature |volume=449 |issue=7159 |pages=189–91 |last1=Silvotti |first1=R. |last2=Schuh |first2=S. |last3=Janulis |first3=R. |last4=Solheim |first4=J. -E. |last5=Bernabei |first5=S. |last6=Østensen |first6=R. |last7=Oswalt |first7=T. D. |last8=Bruni |first8=I. |last9=Gualandi |first9=R. |last10=Bonanno |first10=A. |last11=Vauclair |first11=G. |last12=Reed |first12=M. |last13=Chen |first13=C. -W. |last14=Leibowitz |first14=E. |last15=Paparo |first15=M. |last16=Baran |first16=A. |last17=Charpinet |first17=S. |last18=Dolez |first18=N. |last19=Kawaler |first19=S. |last20=Kurtz |first20=D. |last21=Moskalik |first21=P. |last22=Riddle |first22=R. |last23=Zola |first23=S. |year=2007 |doi=10.1038/nature06143 |pmid=17851517 |s2cid=4342338 |url=http://www.astro.physik.uni-goettingen.de/~schuh/preprints/main.pdf }}</ref>
[[File:Auv0164 pegasus.jpg|thumb|Pegasus from [[Abd al-Rahman al-Sufi|Al-Sufi's]] ''[[Book of Fixed Stars]],'' dated 1009-10 ]]
=== Named stars ===
{| class="wikitable sortable mw-collapsible plainrowheaders"
|-
! scope="col" | Name<ref name="IAU-LSN"/>
! scope="col" | [[Bayer designation]]
! scope="col" | Origin
! scope="col" | Meaning
!Light Years
|-
! scope="row" | [[Alpha Pegasi|Markab]]
| style="text-align: center;" | '''α'''
| [[Arabic language|Arabic]]
| the saddle of the horse
|133
|-
! scope="row" | [[Beta Pegasi|Scheat]]
| style="text-align: center;" | '''β'''
| Arabic
| the upper arm
|196
|-
! scope="row" | [[Gamma Pegasi|Algenib]]
| style="text-align: center;" | '''γ'''
| Arabic
| the side / wing
|391
|-
! scope="row" | [[Epsilon Pegasi|Enif]]
| style="text-align: center;" | '''ε'''
| Arabic
| nose
|690
|-
! scope="row" | [[Zeta Pegasi|Homam]]
| style="text-align: center;" | '''ζ'''
| Arabic
| man of high spirit
|204
|-
! scope="row" | [[Eta Pegasi|Matar]]
| style="text-align: center;" | '''η'''
| Arabic
| lucky rain of shooting stars
|167
|-
! scope="row" | [[Theta Pegasi|Biham]]
| style="text-align: center;" | '''θ'''
| Arabic
| the livestocks
|67
|-
! scope="row" | [[Mu Pegasi|Sadalbari]]
| style="text-align: center;" | '''μ'''
| Arabic
| luck star of the splendid one
|106
|-
! scope="row" | [[Tau Pegasi|Salm]]
| style="text-align: center;" | '''τ'''
| Arabic
| the leathern bucket
|162
|-
! scope="row" | [[Upsilon Pegasi|Alkarab]]
| style="text-align: center;" | '''υ'''
| Arabic
| the bucket-rope
|170
|}
===Deep-sky objects===
[[File:Stephan's Quintet taken by James Webb Space Telescope.jpg|250px|thumb|right|[[Stephan's Quintet]] photographed by the [[James Webb Space Telescope]]]]
[[Messier 15|M15]] (NGC 7078) is a [[globular cluster]] of magnitude 6.4, 34,000 light-years from Earth. It is a Shapley class IV cluster,<ref name=hcob849_11>{{Cite journal | last1=Shapley | first1=Harlow | last2=Sawyer | first2=Helen B. | title=A Classification of Globular Clusters | journal=Harvard College Observatory Bulletin | issue=849 | pages=11–14 |date=August 1927 | bibcode=1927BHarO.849...11S | volume=849 }}</ref> which means that it is fairly rich and concentrated towards its center. M15 was discovered in 1746 by [[Jean-Dominique Maraldi]].{{sfn|Levy|2005|pp=157-158}} Pease 1 is a [[planetary nebula]] located within the [[globular cluster]] and was the first planetary nebula known to exist within a globular cluster.<ref>{{cite web |url=http://www.astropix.com/HTML/SHOW_DIG/M15_Pease1.HTM |title=Globular Cluster M15 and Planetary Nebula Pease 1 |website=www.astropix.com |archive-url=https://web.archive.org/web/20110718101428/http://www.astropix.com/HTML/SHOW_DIG/M15_Pease1.HTM |archive-date=2011-07-18}}</ref> It has an apparent magnitude of 15.5.<ref>{{cite book
| last = Dunlop
| first = Storm
| author-link = Storm Dunlop
| title = Atlas of the Night Sky
| url = https://archive.org/details/collinsatlasofni0000dunl
| url-access = registration
| publisher = [[HarperCollins|Collins]]
| year = 2005
| doi =
| isbn = 0-00-717223-0
}}
</ref>
[[NGC 7331]] is a [[spiral galaxy]] located in Pegasus, 38 million light-years distant with a redshift of 0.0027. It was discovered by musician-astronomer [[William Herschel]] in 1784 and was later one of the first nebulous objects to be described as "spiral" by [[William Parsons, 3rd Earl of Rosse|William Parsons]]. Another of Pegasus's galaxies is [[NGC 7742]], a Type 2 [[Seyfert galaxy]]. Located at a distance of 77 million light-years with a redshift of 0.00555, it is an [[active galaxy]] with a [[supermassive black hole]] at its core. Its characteristic emission lines are produced by gas moving at high speeds around the central black hole.<ref name="AO"/>
Pegasus is also noted for its more unusual galaxies and exotic objects. [[Einstein's Cross]] is a [[quasar]] that has been [[gravitational lensing|lensed]] by a foreground galaxy. The [[elliptical galaxy]] is 400 million light-years away with a [[redshift]] of 0.0394, but the quasar is 8 billion light-years away. The lensed quasar resembles a cross because the gravitational force of the foreground galaxy on its light creates four images of the quasar.<ref name="AO">{{cite book |title=300 Astronomical Objects |last1=Wilkins |first1=Jamie |last2=Dunn |first2=Robert |publisher=Firefly Books |date=2006 |isbn=978-1-55407-175-3}}</ref> [[Stephan's Quintet]] is another unique object located in Pegasus. It is a cluster of five galaxies at a distance of 300 million light-years and a redshift of 0.0215. First discovered by [[Édouard Stephan]], a Frenchman, in 1877, the Quintet is unique for its interacting galaxies. Two of the galaxies in the middle of the group have clearly moms to [[galactic collision|collide]], sparking massive bursts of star formation and drawing off long "tails" of stars. Astronomers have predicted that all five galaxies may eventually merge into one large elliptical galaxy.<ref name="AO"/>
==Namesakes==
USS ''Pegasus'' (AK-48) and USS ''Pegasus'' (PHM-1) are United States navy ships named after the constellation "Pegasus".
The [[Beyblade]] top Storm Pegasus 105RF and its evolutions Galaxy Pegasus W105R2F and Cosmic Pegasus F:D are based on Pegasus constellation.
[[Pegasus Seiya]], main character from the manga and anime [[Saint Seiya]], was named after the constellation Pegasus.
==See also==
* [[Pegasus (Chinese astronomy)]]
==Notes==
{{Notelist}}
==References==
{{Reflist}}
===Cited texts===
* {{Cite book
| title = Uranographie Chinoise
| last = Schlegel
| first = Gustaaf
| publisher = Ch'eng Wen Publishing Company
| ___location = Taipei, Republic of China
| date = 1967
| orig-date = 1875
| language = fr
}}
* {{Cite book
| title =The New Patterns in the Night Sky: Myths and Legends of the Stars
| last = Staal
| first = Julius
| publisher = McDonald and Woodward Publishing Company
| ___location = Blacksburg
| date = 1988
| isbn =0-939923-10-6
}}
*{{cite book | last = Wagman | first = Morton | date = 2003 | title = Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others | publisher = The McDonald & Woodward Publishing Company | ___location = Blacksburg, Virginia | isbn = 978-0-939923-78-6}}
==External links==
{{Commons and category|Pegasus|Pegasus (constellation)}}
* [http://www.allthesky.com/constellations/pegasus/ The Deep Photographic Guide to the Constellations: Pegasus]
* [http://astrojan.nhely.hu/pegasus.htm The clickable Pegasus]
*[http://www.ianridpath.com/startales/pegasus.html Star Tales – Pegasus]
* [https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017056 Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Pegasus)]
{{Stars of Pegasus}}
{{Constellations}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Authority control}}
{{Sky|23|00|00|+|20|00|00|10}}
{{DEFAULTSORT:Pegasus (Constellation)}}
[[Category:Pegasus (constellation)| ]]
[[Category:Constellations]]
[[Category:Northern constellations]]
[[Category:Constellations listed by Ptolemy]]
[[Category:Pegasus]]
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