Editing Sagitta

{{short description|Constellation in the northern celestial hemisphere}}
{{hatnote group|
{{distinguish|text=the southern constellation of [[Sagittarius (constellation)|Sagittarius]]}}
{{other uses}}
}}
{{Use British English|date=November 2020}}
{{Infobox constellation
| name = Sagitta
| abbreviation = Sge<ref name="pa30_469"/>
| genitive = Sagittae<ref name="pa30_469"/>
| pronounce = {{IPAc-en|s|ə|ˈ|dʒ|ɪ|t|ə}} or {{IPAc-en|s|ə|ˈ|ɡ|ɪ|t|ə}} ''Sagítta'',<ref>{{Cite dictionary |url=http://www.lexico.com/definition/Sagitta |archive-url=https://web.archive.org/web/20210415161550/https://www.lexico.com/definition/Sagitta |url-status=dead |archive-date=2021-04-15 |title=Sagitta |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref><br/>genitive {{IPAc-en|s|ə|ˈ|dʒ|ɪ|t|iː}}
| symbolism = the [[Arrow]]<ref name="Kunitzsch"/>
| RA = {{RA|18|57|21.3919}} – {{RA|20|20|44.8677}}<ref name=boundary/>
| dec= {{dec|16.0790844}} to {{dec|21.6436558}}<ref name=boundary/>
| areatotal = 79.9<ref name=tirionconst/>
| arearank = 86th
| numbermainstars = 4
| numberbfstars = 19
| numberstarsplanets = 2
| numberbrightstars = 0
| numbernearbystars = 2 (GJ 745A/B)
| brighteststarname = [[Gamma Sagittae|γ Sge]]
| starmagnitude = 3.51
| neareststarname = Gliese 745
| stardistancely = 28.14
| stardistancepc = 8.63
| numbermessierobjects = 1
| meteorshowers =
| bordering = [[Vulpecula]]<br/>[[Hercules (constellation)|Hercules]]<br/>[[Aquila (constellation)|Aquila]]<br/>[[Delphinus (constellation)|Delphinus]]
| latmax = [[North Pole|90]]
| latmin = [[70th parallel south|70]]
| month = August
| notes=
}}

'''Sagitta''' is a dim but distinctive [[constellation]] in the northern sky. Its name is [[Latin]] for 'arrow', not to be confused with the significantly larger constellation [[Sagittarius (constellation)|Sagittarius]] 'the archer'. It was included among the 48 constellations listed by the 2nd-century astronomer [[Ptolemy]], and it remains one of the [[88 modern constellations]] defined by the [[International Astronomical Union]]. Although it dates to antiquity, Sagitta has no star brighter than 3rd [[apparent magnitude|magnitude]] and has the third-smallest area of any constellation.

[[Gamma Sagittae]] is the constellation's brightest star, with an apparent magnitude of 3.47. It is an aging [[red giant]] star 90% as massive as the Sun that has cooled and expanded to a radius 54 times greater than it. [[Delta Sagittae|Delta]], [[Epsilon Sagittae|Epsilon]], [[Zeta Sagittae|Zeta]], and [[Theta Sagittae]] are each [[Star system|multiple]] stars whose components can be seen in small telescopes. [[V Sagittae]] is a [[cataclysmic variable]]—a [[Binary star|binary star system]] composed of a [[white dwarf]] accreting mass of a donor star that is expected to go [[nova]] and briefly become the most [[Luminosity|luminous]] star in the [[Milky Way]] and one of the brightest stars in our sky around the year 2083. Two star systems in Sagitta are known to have Jupiter-like planets, while a third—[[15 Sagittae]]—has a [[brown dwarf]] companion.
{{TOC limit|3}}

==History==
[[File:Sidney Hall - Urania's Mirror - Delphinus, Sagitta, Aquila, and Antinous.jpg|thumb|alt=Drawing of a dolphin, eagle, archer, and arrow overlaid on a medieval star chart|Sagitta can be seen above [[Aquila (constellation)|Aquila]] in this plate from ''[[Urania's Mirror]]'' (1825).]]
The [[classical Greece|ancient Greeks]] called Sagitta {{lang|grc|Oistos}} 'the arrow',<ref name="Kunitzsch"/> and it was one of the 48 constellations described by [[Ptolemy]].<ref name=ridpathsag/> It was regarded as the weapon that [[Hercules]] used to kill the eagle ({{lang|la|Aquila}}) of [[Jupiter (mythology)|Jove]]<!--wouldn't the Greeks have said "Zeus"?--> that perpetually gnawed [[Prometheus]]' liver.<ref name="hyginus_14">{{cite web |url=http://www.theoi.com/Text/HyginusAstronomica.html#15 |title=Astronomica |author=Hyginus |translator=Mary Grant |website=Theoi Project |access-date=31 January 2020}}</ref> Sagitta is located beyond the north border of [[Aquila (constellation)|Aquila]], the Eagle. An amateur naturalist, polymath [[Richard Hinckley Allen]] proposed that the constellation could represent the arrow shot by Hercules towards the adjacent [[Stymphalian birds]] (which feature in [[Labours of Hercules|Hercules' sixth labour]]) who had claws, beaks, and wings of iron, and who lived on human flesh in the marshes of [[Arcadia (ancient region)|Arcadia]]—denoted in the sky by the constellations Aquila the Eagle, [[Cygnus (constellation)|Cygnus 'the Swan']], and [[Lyra|Lyra 'the Vulture']]—and still lying between them, whence the title [[Herculea]].<ref>{{cite book|first=Richard Hinckley | last=Allen|title=Star-Names and Their Meanings|pages =349–351 | url=https://books.google.com/books?id=l8V2DY3tQMgC&q=Star-Names+and+Their+Meanings | year=1963 | orig-date=1899 | publisher=Dover Publications |location=New York | isbn=978-0-486-21079-7 }}</ref> Greek scholar [[Eratosthenes]] claimed it as the arrow with which [[Apollo]] exterminated the [[Cyclopes]].<ref name="hyginus_14"/> The Romans named it Sagitta.<ref>{{Cite book|title=The Star Atlas Companion: What You Need to Know about the Constellations|last=Bagnall|first= Philip M. |date=2012|publisher=[[Springer Science+Business Media|Springer]] |pages= 386–389 | location=New York | isbn=978-1-4614-0830-7|oclc=794225463}}</ref> In Arabic, it became ''al-sahm'' 'arrow', though this name became ''Sham'' and was transferred to [[Alpha Sagittae]] only. The Greek name has also been mistranslated as {{lang|el-latn|ὁ istos}} 'the loom' and thus in Arabic ''al-nawl''. It was also called ''al-'anaza'' 'pike/javelin'.<ref name="Kunitzsch">{{cite journal |url= http://opar.unior.it/473/1/P._Kunitzsch_pp.19-28_pdf.pdf |title= Albumasariana |journal=Annali dell'Università degli studi di Napoli "L'Orientale" |publisher=Rivista del Dipartimento di Studi Asiatici e del Dipartimento di Studi e Ricerche su Africa e Paesi Arabi |first=Paul |last= Kunitzsch |volume=62 |page=4 |date=2002 |issn=0393-3180 }}</ref>

== Characteristics ==
The four brightest stars make up an arrow-shaped [[Asterism (astronomy)|asterism]] located due north of the bright star [[Altair]].<ref name="moore366">{{Cite book |last=Moore |first=Patrick |title=The Observer's Year: 366 Nights in the Universe |publisher=[[Springer Science & Business Media]] |year=2005 |isbn=978-1-85233-884-8 |location=New York |page=10 |author-link=Patrick Moore}}</ref> Covering 79.9 square degrees and hence 0.194% of the sky, Sagitta ranks 86th of the [[88 modern constellations]] by area. Only [[Equuleus]] and [[Crux]] are smaller.<ref name=tirionconst/> Sagitta is most readily observed from the late spring to early autumn to northern hemisphere observers, with midnight [[culmination]] occurring on 17 July.<ref name=thompson2>{{cite book|title=Illustrated Guide to Astronomical Wonders: From Novice to Master Observer|author1=Thompson, Robert Bruce|author2=Barbara Fritchman|url=https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA392|page=392|isbn=978-0-596-52685-6|publisher=O'Reilly Media, Inc.|location=Sebastopol, California|year=2007}}</ref> Its position in the [[Northern Celestial Hemisphere]] means that the whole [[constellation]] is visible to observers north of [[69th parallel south|69°S]].<ref name=tirionconst>{{cite web| url=http://www.ianridpath.com/constellations2.html | title=Constellations: Lacerta–Vulpecula | work= Star Tales |author=Ridpath, Ian | access-date= 22 May 2015| author-link=Ian Ridpath }}</ref>{{efn|1=While parts of the constellation technically rise above the horizon to observers between the 69°S and 73°S, stars within a few degrees of the horizon are to all intents and purposes unobservable.<ref name=tirionconst/>}} Sagitta is bordered by [[Vulpecula]] to the north, [[Hercules (constellation)|Hercules]] to the west, Aquila to the south, and [[Delphinus (constellation)|Delphinus]] to the east. The three-letter abbreviation for the constellation, as adopted by the [[International Astronomical Union]] in 1922, is "Sge"; American astronomer [[Henry Norris Russell]], who devised the code, had to resort to using the [[Genitive case|genitive]] form of the name to come up with a letter to include ('e') that was not in the name of the constellation Sagittarius.<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 (US magazine)|Popular Astronomy]] | volume=30 | page=469 | bibcode=1922PA.....30..469R | year=1922 }}</ref> The official constellation boundaries, as set by Belgian astronomer [[Eugène Joseph Delporte|Eugène Delporte]] in 1930, are defined by a polygon of twelve segments (''illustrated in infobox''). In the [[equatorial coordinate system]], the [[right ascension]] coordinates of these borders lie between {{RA|18|57.2}} and {{RA|20|20.5}}, while the [[declination]] coordinates are between 16.08° and 21.64°.<ref name="boundary">{{Cite web | title=Sagitta, Constellation Boundary | publisher=[[International Astronomical Union]] | url=https://www.iau.org/public/themes/constellations/#sge | access-date=20 October 2020 }}</ref>

==Notable features==
===Stars===
{{see also|List of stars in Sagitta}}
Celestial cartographer [[Johann Bayer]] gave [[Bayer designation]]s to eight stars, labelling them Alpha to Theta. English astronomer [[John Flamsteed]] added the letters x, mistaken as [[Chi (letter)|Chi]] (χ), y and z to 13, 14, and 15 Sagittae in his ''Catalogus Britannicus''. All three were dropped by later astronomers [[John Bevis]] and [[Francis Baily]].<ref name=wagman>{{cite book | last = Wagman | first = Morton | year = 2003 | title = Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others |pages=266–267, 515 | publisher = The McDonald & Woodward Publishing Company | location = Blacksburg, Virginia | isbn = 978-0-939923-78-6 }}</ref>

====Bright stars====
Ptolemy saw the constellation's brightest star [[Gamma Sagittae]] as marking the arrow's head,<ref name="ridpathsag">{{cite web |last=Ridpath |first=Ian |author-link=Ian Ridpath |title=Sagitta |url=http://www.ianridpath.com/startales/sagitta.html |access-date=22 May 2015 |work=Star Tales}}</ref> while Bayer saw Gamma, Eta, and Theta as depicting the arrow's shaft.<ref name=wagman/> Gamma Sagittae is a [[red giant]] of spectral type M0&nbsp;III,<ref name=strassmeier>{{cite journal|bibcode=2018A&A...612A..45S|title=PEPSI deep spectra. II. Gaia benchmark stars and other M-K standards|journal=[[Astronomy and Astrophysics]]|volume=612|pages=A45|last1=Strassmeier|first1=K. G. |last2=Ilyin|first2=I.|last3=Weber|first3=M.|year=2018|arxiv=1712.06967|doi=10.1051/0004-6361/201731633|s2cid=119244142}}</ref> and magnitude 3.47. It lies at a distance of {{val|258|4|ul=light-years}} 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=653–664 | date=2007 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | arxiv=0708.1752| s2cid=18759600 }}</ref> With around 90% of the Sun's mass,<ref name=stock>{{cite journal
 | title=Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search
 | last1=Stock | first1=Stephan | last2=Reffert | first2=Sabine
 | last3=Quirrenbach | first3=Andreas | last4=Hauschildt | first4=P.
 | journal=Astronomy and Astrophysics
 | volume=616 | pages=A33 | year=2018
 | bibcode=2018A&A...616A..33S | arxiv=1805.04094
 | doi=10.1051/0004-6361/201833111 | s2cid=119361866 }}</ref><ref name=Neilson2008>{{cite journal
 | last1=Neilson | first1=Hilding R. | last2=Lester | first2=John B.
 | title=Determining parameters of cool giant stars by modeling spectrophotometric and interferometric observations using the SAtlas program
 | journal=Astronomy and Astrophysics
 | volume=490 | issue=2 | pages=807–10 | date=2008
 | bibcode=2008A&A...490..807N | arxiv=0809.1875
 | doi=10.1051/0004-6361:200810627 | s2cid=1586125 }}</ref> it has a radius 54 times that of the Sun and is 575 times as bright. It is most likely on the [[red-giant branch]] of its [[stellar evolution|evolutionary]] lifespan, having exhausted its core hydrogen and now burning it in a surrounding shell.<ref name=stock/><!-- cites previous 3 sentences -->

[[Delta Sagittae]] is the second-brightest star in the constellation and is a binary. Delta and Zeta depicted the spike according to Bayer.{{sfn|Wagman|2003|p=515}} The Delta Sagittae system is composed of a [[red supergiant]] of spectral type M2&nbsp;II<ref name=Eaton/> that has 3.9 times the Sun's mass and 152 times its radius and a blue-white B9.5V<ref name=Eaton/> [[main sequence]] star that is 2.9 times as massive as the Sun. The two orbit each other every ten years.<ref name=Eaton>{{cite journal|title=Winds and accretion in delta Sagittae|author=Eaton, Joel A.|author2=Hartkopf, William I.|author3=McAlister, Harold A.|author4=Mason, Brian D.|journal=[[Astronomical Journal]]|volume=109|number=4|pages=1856–1866|date=1995|bibcode=1995AJ....109.1856E|doi=10.1086/117412}}</ref> [[Zeta Sagittae]] is a triple star system,<ref name=Eggleton2008>{{citation
 | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A.
 | title=A catalogue of multiplicity among bright stellar systems
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=389 | issue=2 | pages=869–879 | date=September 2008
 | bibcode=2008MNRAS.389..869E | doi=10.1111/j.1365-2966.2008.13596.x
 | doi-access=free | arxiv=0806.2878 | s2cid=14878976 | postscript=. }}</ref> approximately {{val|326|u=light-years}} from Earth. The primary and secondary are A-type stars.<ref name=Christy1969>{{citation
 | last1=Christy | first1=James W. | last2=Walker | first2=R. L. Jr.
 | title=MK Classification of 142 Visual Binaries | postscript=.
 | journal=Publications of the Astronomical Society of the Pacific
 | volume=81 | issue=482 | page=643 | date=October 1969
 | doi=10.1086/128831 | bibcode=1969PASP...81..643C | doi-access=free }}</ref><ref name=Cowley1969>{{citation | display-authors=1
 | last1=Cowley | first1=A. | last2=Cowley | first2=C.
 | last3=Jaschek | first3=M. | last4=Jaschek | first4=C.
 | title=A study of the bright A stars. I. A catalogue of spectral classifications
 | journal=Astronomical Journal | postscript=.
 | volume=74 | pages=375–406 | date=April 1969
 | doi=10.1086/110819 | bibcode=1969AJ.....74..375C }}</ref>

In his ''Uranometria'', Bayer depicted Alpha, [[Beta Sagittae|Beta]], and [[Epsilon Sagittae]] as the fins of the arrow.{{sfn|Wagman|2003|p=515}} Also known as Sham, Alpha is a yellow [[bright giant]] star of [[Stellar classification|spectral class]] G1&nbsp;II with an [[apparent magnitude]] of 4.38, which lies at a distance of {{val|382|8|u=light-years}} from Earth.<ref name=Gaia-DR2alpha>{{cite DR2|1824277055360974720}}</ref> Four times as massive as the Sun, it has swollen and brightened to 21&nbsp;times the Sun's radius and 340&nbsp;times its [[luminosity]].<ref name="vanBelle2009" /><ref name=kalersham>{{cite web| first=James B. | last=Kaler | title=Sham | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/sham.html | access-date=22 May 2015}}</ref> Also of magnitude 4.38, Beta is a G-type [[giant star|giant]] located {{val|420|10|u=light-years}} distant from Earth.<ref name=Gaia-DR2beta>{{cite DR2|1823991938300446336}}</ref> Estimated to be around 129&nbsp;million years old, it is 4.33&nbsp;times as massive as the Sun,<ref name=Liu2014>{{cite journal | title=The Lithium Abundances of a Large Sample of Red Giants | display-authors=1 | last1=Liu | first1=Y. J. | last2=Tan | first2=K. F. | last3=Wang | first3=L. | last4=Zhao | first4=G. | last5=Sato | first5=Bun'ei | last6=Takeda | first6=Y. | last7=Li | first7=H. N. | journal=[[The Astrophysical Journal]] | arxiv=1404.1687 | volume=785 | issue=2 | id=94 | page=12 | date=2014 | doi=10.1088/0004-637X/785/2/94 | bibcode=2014ApJ...785...94L | s2cid=119226316 }}</ref> and has expanded to roughly 27 times its radius.<ref name=vanBelle2009>{{cite journal | title=Supergiant temperatures and linear radii from near-infrared interferometry | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=394 | issue=4 | page=1925 | year=2009 | last1=Van Belle | first1=G. T. | last2=Creech-Eakman | first2=M. J. | last3=Hart | first3=A. | bibcode=2009MNRAS.394.1925V | arxiv=0811.4239 | doi=10.1111/j.1365-2966.2008.14146.x | doi-access=free | s2cid=118372600 }}</ref> Epsilon Sagittae is a [[double star]] whose component stars can be seen in a small telescope.<ref name="turnleft">{{cite book|last=Consolmagno|first=Guy |title=Turn Left at Orion: Hundreds of Night Sky Objects to See in a Home Telescope – and How to Find Them|publisher=[[Cambridge University Press]]|location=Cambridge, United Kingdom|year=2019 | orig-date=1989 |page=138 |isbn=978-1-108-45756-9|url=https://books.google.com/books?id=D2JjDwAAQBAJ&pg=PA139}}</ref> With an apparent magnitude of 5.77,<ref name=Mason2014/> the main star is a 331-million-year-old yellow giant of spectral type G8&nbsp;III around 3.09&nbsp;times as massive as the Sun,<ref name=takeda14>{{cite journal | title=Spectroscopic study on the beryllium abundances of red giant stars | journal=[[Publications of the Astronomical Society of Japan]] | volume=66 | issue=5 | page=91 | year=2014 | last1=Takeda | first1=Yoichi | last2=Tajitsu | first2=Akito | doi=10.1093/pasj/psu066 | bibcode=2014PASJ...66...91T | arxiv=1406.7066| s2cid=119283677 }}</ref> that has swollen to {{val|18.37|0.65|0.88}} its radius.<ref name="GaiaDR2epsilon"/> It is {{val|580|10|u=light-years}} distant.<ref name="GaiaDR2epsilon">{{Cite DR2|4321830946398475776}}</ref> The visual companion of magnitude 8.35 is 87.4&nbsp;[[arcseconds]] distant,<ref name=Mason2014>{{cite journal| last1=Mason | first1=B. D. | last2=Wycoff | first2=G. L. | last3=Hartkopf | first3=W. I. | last4=Douglass | first4=G. G. | last5=Worley | first5=C. E. | title=The Washington Visual Double Star Catalog | journal=[[Nature (journal)|Nature]] | year=2014 | volume=122 | issue=6 | page=3466 | bibcode=2001AJ....122.3466M | doi = 10.1086/323920 | doi-access=free }}</ref> but is an unrelated [[blue supergiant]] around {{val|7000|fmt=commas|u=light-years}} distant from Earth.<ref name="GaiaDR2comp">{{cite DR2|4321830980758181760}}</ref>

[[Eta Sagittae]] is an orange giant of spectral class K2&nbsp;III<ref name=Roman1952>{{citation
 | title=The Spectra of the Bright Stars of Types F5-K5
 | last=Roman | first=Nancy G. | postscript=.
 | journal=Astrophysical Journal
 | volume=116 | page=122 | date=July 1952
 | doi=10.1086/145598 | bibcode=1952ApJ...116..122R | doi-access=free }}</ref> with a magnitude of 5.09.<ref name=Argue1966>{{citation
 | last=Argue | first=A. N. | postscript=.
 | title=UBV photometry of 550 F, G and K type stars
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=133 | pages=475–493 | year=1966
 | issue=4 | bibcode=1966MNRAS.133..475A | doi=10.1093/mnras/133.4.475| doi-access=free}}</ref> Located {{val|155.9|0.9|u=light-years}} from Earth, it has a 61.1% chance of being a member of the [[Hyades (star cluster)|Hyades]]–[[Pleiades]] stream of stars that share a [[Stellar kinematics|common motion through space]].<ref name=Famaey2005>{{cite journal| last1=Famaey | first1=B. | last2=Jorissen | first2=A. | last3=Luri | first3=X. | last4=Mayor | first4=M. | last5=Udry | first5=S. | last6=Dejonghe | first6=H. | last7=Turon | first7=C. | title=Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters | journal=[[Astronomy and Astrophysics]] | volume=430 | pages=165–186 | date=2005 | doi=10.1051/0004-6361:20041272 | bibcode=2005A&A...430..165F | arxiv=astro-ph/0409579 | s2cid=17804304 }}</ref> [[Theta Sagittae]] is a double star system, with components 12 arcseconds apart visible in a small telescope.<ref name="turnleft"/> At magnitude 6.5, the brighter is a yellow-white main sequence star of spectral type F3&nbsp;V,<ref name="abt1985">{{cite journal |last=Abt |first=Helmut A. |title=Visual multiples. VIII. 1000 MK types |journal=The Astrophysical Journal Supplement Series |date=1985 |bibcode= 1985ApJS...59...95A |volume=59 |pages=95–112 |doi=10.1086/191064|doi-access=free }}</ref> located {{val|146.1|0.2|u=light-years}} from Earth.<ref name=Gaia-DR2tet1>{{cite DR2|1829590548393010560}}</ref> The 8.8-magnitude fainter companion is a main sequence star of spectral type G5&nbsp;V. A 7.4-magnitude orange giant of spectral type K2&nbsp;III is also visible {{val|91|ul="}} from the binary pair,<ref name="abt1985"/> located {{val|842|9|u=light-years}} away.<ref name=Gaia-DR2tet2>{{cite DR2|1829590410954063744}}</ref>

====Variable stars====

[[Image:Wolf-Rayet 124 (NIRCam and MIRI composite image).tif|thumb|right|300px|[[James Webb Space Telescope]] image of [[WR 124]] in Sagitta. [[NIRCam]] and [[Mid-Infrared Instrument|MIRI]] composite]]

Variable stars are popular targets for amateur astronomers, their observations providing valuable contributions to understanding star behaviour.<ref>{{cite web |last=Tooke |first=Owen |title=Variables: What Are They and Why Observe Them? |url=https://www.aavso.org/variables-what-are-they-why-observe-them |publisher=AAVSO | date=24 August 2017 |access-date=14 October 2020}}</ref> [[R Sagittae]] is a member of the rare [[RV Tauri variable]] class of star. It ranges in magnitude from 8.2 to 10.4.<ref name="Levy 1998">{{cite book|last=Levy|first=David H.|title=Observing Variable Stars: A Guide for the Beginner|publisher=[[Cambridge University Press]]|location=Cambridge, United Kingdom|date=1998|pages=152–153|isbn=978-0-521-62755-9|url=https://books.google.com/books?id=5-O2cd937FMC&pg=PA153}}</ref> It is around {{val|8100|fmt=commas|u=light-years}} distant.<ref name=dr2R>{{cite DR2|1808748613981554176}}</ref> It has a radius {{val|61.2|12.4|9.9}} times that of the Sun, and is {{val|2329|744|638|fmt=commas}} as luminous, yet most likely is less massive than the Sun. An aging star, it has moved on from the [[asymptotic giant branch]] of stellar evolution and is on its way to becoming a [[planetary nebula]].<ref name=bodikiss>{{cite journal |doi=10.3847/1538-4357/aafc24 |title=Physical Properties of Galactic RV Tauri Stars from Gaia DR2 Data |journal=[[The Astrophysical Journal]] |volume=872 |issue=1 |page=60 |year=2019 |last1=Bódi |first1=A. |last2=Kiss |first2=L. L. |bibcode=2019ApJ...872...60B |arxiv=1901.01409 |s2cid=119099605 |doi-access=free }}</ref> [[FG Sagittae]] is a "born again" star, a highly luminous star around {{val|4000|fmt=commas|u=light-years}} distant from Earth.<ref name=dr2FG>{{cite DR2|1828750899461025536}}</ref> It reignited fusion of a helium shell shortly before becoming a white dwarf, and has expanded first to a blue supergiant and then to a K-class [[supergiant]] in less than 100 years.<ref name=jurcsik1999>{{cite journal |bibcode=1999NewAR..43..415J |title=The remarkable evolution of the post-AGB star FG Sge |last1=Jurcsik |first1=Johanna |last2=Montesinos |first2=Benjamín. |journal=New Astronomy Reviews |year=1999 |volume=43 |issue=6 |page=415 |doi=10.1016/S1387-6473(99)00098-6 |url=http://real.mtak.hu/2086/1/K.pdf }}</ref> It is surrounded by a faint (visual magnitude 23) planetary nebula, Henize 1–5, that formed when FG Sagittae first left the asymptotic giant branch.<ref name=rosenbush2015>{{cite journal |bibcode=2015Ap.....58...46R |title=Photometry, Spectrometry, and Polarimetry of FG Sge in the Active State |last1=Rosenbush |first1=A. É. |last2=Efimov |first2=Yu. S. |s2cid=121128187 |journal=Astrophysics |year=2015 |volume=58 |issue=1 |page=46 |doi=10.1007/s10511-015-9365-x }}</ref>

[[S Sagittae]] is a [[classical Cepheid]] that varies from magnitude 5.24 to 6.04 every 8.38&nbsp;days. It is a yellow-white supergiant that pulsates between spectral types F6&nbsp;Ib and G5&nbsp;Ib.<ref name=AAVSOS>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=27343 |title=S Sagittae |author =Watson, Christopher |date=4 January 2010|publisher=AAVSO |access-date=22 May 2015}}</ref> Around 6 or 7 times as massive and 3,500 times as luminous as the Sun,<ref name=kalerSSge>{{cite web| first=James B. | last=Kaler | title=S Sagittae | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/ssge.html | date= 4 October 2013|access-date=22 May 2015}}</ref> it is located around {{val|5100|fmt=commas|u=light-years}} from Earth.<ref name=Gaia-DR2S>{{cite DR2|1820309639468685824}}</ref> [[HD 183143]] is a remote highly luminous star around {{val|7900|fmt=commas|u=light-years}} away,<ref name=dr2>{{cite DR2|4323280515006629760}}</ref> that has been classified as a blue [[hypergiant]].<ref name=chentsov>{{cite journal|last=Chentsov|first=E. L.|title=HD 183143: A Hypergiant|journal=Astronomy Letters|volume=30|issue=5|year=2004|pages=325–331|doi=10.1134/1.1738155|bibcode=2004AstL...30..325C|s2cid=121435951}}</ref> [[Infrared]] bands of ionised [[buckminsterfullerene]] molecules have also been found in its spectrum.<ref name=c60>{{cite journal|bibcode=2015ApJ...812L...8W|arxiv=1509.06818|title=Identification of More Interstellar C60+ Bands|journal=The Astrophysical Journal Letters|volume=812|pages=L8|last1=Walker|first1=G. A. H.|last2=Bohlender|first2=D. A.|last3=Maier|first3=J. P.|last4=Campbell|first4=E. K.|year=2015|issue=1|doi=10.1088/2041-8205/812/1/L8|s2cid=118598331}}</ref> [[WR 124]] is a [[Wolf–Rayet star]] moving at great speed surrounded by a nebula of ejected gas.<ref name=crowther>{{cite journal|bibcode=1999A&A...350.1007C|title=Wolf–Rayet nebulae as tracers of stellar ionizing fluxes. I. M1-67|journal=Astronomy and Astrophysics|volume=350|page=1007|last1=Crowther|first1=Paul A.|last2=Pasquali|first2=A.|last3=De Marco|first3=Orsola|author3-link=Orsola De Marco|last4=Schmutz|first4=W.|last5=Hillier|first5=D. J.|last6=De Koter|first6=A.|year=1999|arxiv = astro-ph/9908200 }}</ref>

[[U Sagittae]] is an eclipsing binary that varies between magnitudes 6.6 and 9.2 over 3.4&nbsp;days, making it a suitable target for enthusiasts with small telescopes.<ref name=moore366/> There are two component stars—a blue-white star of spectral type B8&nbsp;V and an ageing star that has cooled and expanded into a yellow subgiant of spectral type G4&nbsp;III-IV. They orbit each other close enough that the cooler subgiant has filled its [[Roche lobe]] and is passing material to the hotter star, and hence it is a [[semidetached binary]] system.<ref>{{cite journal |last=Malkov |first=Oleg Yu |title=Semidetached double-lined eclipsing binaries: Stellar parameters and rare classes |journal=Monthly Notices of the Royal Astronomical Society |date=2020 |volume=491 |issue=4 |pages=5489–5497| bibcode= 2020MNRAS.491.5489M |doi=10.1093/mnras/stz3363|doi-access=free }}</ref> The system is {{val|900|10|u=light-years}} distant.<ref name=Gaia-DR2u>{{cite DR2|4516549576568929408}}</ref> Near U Sagittae is [[X Sagittae]], a [[semiregular variable]] ranging between magnitudes 7.9 and 8.4 over 196&nbsp;days.<ref name=moore366/> A [[carbon star]], X Sagittae has a surface temperature of {{val|2576|fmt=commas|ul=K}}.<ref>{{cite journal |last1=Taranova |first1=O.G. | first2=V. I. | last2=Shenavrin |title=JHKLM Photometry for Carbon Stars |journal=[[Astronomy Letters]] |date=2004 |volume=30 |issue=8 |pages=605–622 |doi=10.1134/1.1784497|bibcode=2004AstL...30..549T |s2cid=119984131 }}</ref>

Located near 18 Sagittae is [[V Sagittae]], the prototype of the [[V Sagittae variable]]s, [[cataclysmic variable]]s that are also [[super soft X-ray source]]s.<ref name="Levy 1998"/> It is expected to become a [[luminous red nova]] when the two stars merge around the year 2083, and briefly become the most luminous star in the [[Milky Way]] and one of the brightest stars in Earth's sky.<ref name=2020-01>{{Cite web|url=https://phys.org/news/2020-01-binary-star-sagittae-bright-nova.html|title=Binary star V Sagittae to explode as very bright nova by century's end| last= Lavalle| first= Mimi |website=phys.org|language=en-us|access-date=9 January 2020| date=7 January 2020}}</ref><ref>{{Cite web|url=http://m.cnn.com/en/article/h_f7a7fda778b24834ac5316152cc63433|title=There will be a new brightest star in the sky, when it explodes in about 60 years|publisher=CNN|access-date=9 January 2020|date=8 Jan 2020|archive-date=13 January 2020|archive-url=https://web.archive.org/web/20200113183819/http://m.cnn.com/en/article/h_f7a7fda778b24834ac5316152cc63433|url-status=dead}}</ref> [[WZ Sagittae]] is another cataclysmic variable, composed of a [[white dwarf]] that has about 85% the mass of the Sun, and low-mass star companion that has been calculated to be a [[brown dwarf]] of spectral class L2 that is only 8% as massive as the Sun.<ref name="apj667">{{cite journal | author=Steeghs, Danny | author2=Howell, Steve B. | author3=Knigge, Christian | author4=Gänsicke, Boris T. | author5=Sion, Edward M. | author6=Welsh, William F. | title=Dynamical Constraints on the Component Masses of the Cataclysmic Variable WZ Sagittae | journal=[[The Astrophysical Journal]] | volume=667 | issue=1 | pages=442–447 |date=September 2007 | doi=10.1086/520702 | bibcode=2007ApJ...667..442S|arxiv = 0706.0987 | s2cid=209833493 }}</ref> Normally a faint object dimmer than magnitude 15, it flared up in 1913, 1946 and 1978 to be visible in binoculars.<ref name=moore366/> The [[black widow pulsar]] (B1957+20) is the second [[millisecond pulsar]] ever discovered.<ref>{{cite journal|last1=Fruchter|first1=A. S.|last2=Stinebring|first2=D. R.|last3=Taylor|first3=J. H.|year=1988|title=A millisecond pulsar in an eclipsing binary|journal=[[Nature (journal)|Nature]]|volume=333|issue=6170|pages=237–239 |bibcode=1988Natur.333..237F|doi=10.1038/333237a0|s2cid=4337525}}</ref> It is a massive [[neutron star]] that is [[Ablation|ablating]] its brown dwarf-sized companion which causes the pulsar's radio signals to [[Attenuation|attenuate]] as they pass through the outflowing material.<ref>{{Cite web|url=https://chandra.harvard.edu/photo/2003/b1957/|title=B1957+20: A Cocoon Found Inside the Black Widow's Web|website=Chandra|access-date=23 October 2020}}</ref>

====Stars with exoplanets====
[[Image:Messier 71 Hubble WikiSky.jpg|thumb|right|alt=Several hundred stars of different brightnesses and colours scattered on a black background|[[Messier 71]] globular cluster]]

[[HD 231701]] is a [[F-type main sequence star|yellow-white main sequence star]] hotter and larger than the Sun, with a [[Jupiter]]-like [[planet]] that was discovered in 2007 by the [[methods of detecting extrasolar planets#Radial velocity|radial velocity technique]]. The planet orbits at a distance of {{Val|0.57|ul=AU}} from the star with a period of 141.6&nbsp;days.<ref name="Fischer2007">{{cite journal | title=Five Intermediate-Period Planets from the N2K Sample | last1=Fischer | first1=Debra A. | last2=Vogt | first2=Steven S. | last3=Marcy | first3=Geoffrey W. | last4=Butler | first4=R. Paul | last5=Sato | first5=Bun'ei | last6=Henry | first6=Gregory W. | last7=Robinson | first7=Sarah | last8=Laughlin | first8=Gregory | last9=Ida | first9=Shigeru | journal=[[The Astrophysical Journal]] | volume=669 | issue=2 | pages=1336–1344 | year=2007 | arxiv=0704.1191 | bibcode=2007ApJ...669.1336F | doi=10.1086/521869 | s2cid=7774321 }}</ref> It has a mass of at least 1.13 Jupiter masses.<ref>{{cite journal
 | title=Radial Velocities from the N2K Project: Six New Cold Gas Giant Planets Orbiting HD 55696, HD 98736, HD 148164, HD 203473, and HD 211810
 | last1=Ment | first1=Kristo | last2=Fischer | first2=Debra A.
 | last3=Bakos | first3=Gaspar | last4=Howard | first4=Andrew W.
 | last5=Isaacson | first5=Howard | display-authors=1
 | journal=The Astronomical Journal
 | volume=156 | issue=5 | at=213 | year=2018
 | arxiv=1809.01228 | bibcode=2018AJ....156..213M
 | doi=10.3847/1538-3881/aae1f5 | s2cid=119243619 | doi-access=free }}</ref> 

HAT-P-34 is a star {{val|1.392|0.047}} times as massive as the Sun with {{val|1.535|0.135|0.102}} times its radius and {{val|3.63|0.75|0.51}} times its luminosity. With an apparent magnitude of 10.4,<ref name="Bakos2012"/> it is {{val|819|9|u=light-years}} distant.<ref name=Gaia-DR2hat34>{{cite DR2|1810218734055374720}}</ref> A planet {{val|3.328|0.211}} times as massive as Jupiter was discovered transiting it in 2012. With a period of 5.45&nbsp;days and a distance of {{val|0.06|u=AU}} from its star, it has an estimated surface temperature of {{val|1520|60|fmt=commas|u=K}}.<ref name="Bakos2012">{{cite journal | title=HAT-P-34b – HAT-P-37b: Four Transiting Planets More Massive Than Jupiter Orbiting Moderately Bright Stars | last1=Bakos | first1=G. Á. | last2=Hartman | first2=J. D. | last3=Torres | first3=G. | last4=Béky | first4=B. | last5=Latham | first5=D. W. | last6=Buchhave | first6=L. A. | last7=Csubry | first7=Z. | last8=Kovács | first8=Géza | last9=Bieryla | first9=A. | last10=Quinn | first10=S. | last11=Szklenár | first11=T. | last12=Esquerdo | first12=G. A. | last13=Shporer | first13=A. | last14=Noyes | first14=R. W. | last15=Fischer | first15=D. A. | last16=Johnson | first16=J. A. | last17=Howard | first17=A. W. | last18=Marcy | first18=G. W. | last19=Sato | first19=B. | last20=Penev | first20=K. | last21=Everett | first21=M. | last22=Sasselov | first22=D. D. | last23=Fűrész | first23=G. | last24=Stefanik | first24=R. P. | last25=Lázár | first25=J. | last26=Papp | first26=I. | last27=Sári | first27=P. | journal=[[The Astronomical Journal]] | volume=144 | issue=1 | pages=19–32 | date=2012 | arxiv=1201.0659 | bibcode=2012AJ....144...19B | doi=10.1088/0004-6256/144/1/19 | s2cid=119291677 }}</ref> 

[[15 Sagittae]] is a [[solar analog]]—a star similar to the Sun, with {{val|1.08|0.04}} times its mass, {{val|1.115|0.021}} times its radius and {{val|1.338|0.03}} times its luminosity. It has an apparent magnitude of 5.80.<ref name=Anderson2012>{{citation
 | title=XHIP: An extended hipparcos compilation
 | last1=Anderson | first1=E. | last2=Francis | first2=Ch.
 | journal=Astronomy Letters | postscript=.
 | arxiv=1108.4971 | volume=38 | issue=5 | page=331 | year=2012
 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref> It has an L4 brown dwarf substellar companion that is around the same size as Jupiter but 69 times as massive with a surface temperature of between 1,510 and {{val|1850|fmt=commas|u=K}}, taking around 73.3&nbsp;years to complete an orbit around the star.<ref name=Crepp2012/> The system is estimated to be {{val|2.5|1.8}} billion years old.<ref name=Crepp2012>{{cite journal | last1=Crepp | first1=Justin R. | last2=Johnson | first2=John Asher | last3=Fischer | first3=Debra A. | last4=Howard | first4=Andrew W. | last5=Marcy | first5=Geoffrey W. | last6=Wright | first6=Jason T. | last7=Isaacson | first7=Howard | last8=Boyajian | first8=Tabetha | last9=von Braun | first9=Kaspar | last10=Hillenbrand | first10=Lynne A. | last11=Hinkley | first11=Sasha | last12=Carpenter | first12=John M. | last13=Brewer | first13=John M. | title=The Dynamical Mass and Three-Dimensional Orbit of HR7672B: A Benchmark Brown Dwarf with High Eccentricity | journal=[[The Astrophysical Journal]] | volume=751 | issue=2 | id=97 | page=14 | date=2012 | arxiv=1112.1725 | bibcode=2012ApJ...751...97C | doi=10.1088/0004-637X/751/2/97| s2cid=16113054 }}</ref>

===Deep-sky objects===
The band of the Milky Way and the [[Great Rift (astronomy)|Great Rift]] within it pass though Sagitta, with Alpha, Beta and Epsilon Sagittae marking the Rift's border.<ref name="crossen 2004">{{cite book|author1=Crossen, Craig |author2=Rhemann, Gerald |title=Sky Vistas: Astronomy for Binoculars and Richest-Field Telescopes|publisher=[[Springer Science+Business Media|Springer]]|location=New York|orig-date=2004 | year=2012 | page=150 | url=https://books.google.com/books?id=3vELBwAAQBAJ&pg=PA150 | isbn=978-3-709-10626-6}}</ref> Located between Beta and Gamma Sagittae is [[Messier 71]],<ref name=moore366/> a very loose [[globular cluster]] mistaken for some time for a dense [[open cluster]].<ref name=tt/> At a distance of about {{val|13000|fmt=commas|u=light-years}} from Earth,<ref name=inglis2017>{{cite book |last1=Inglis |first1=Mike |title=Astronomy of the Milky Way: The Observer's Guide to the Northern Sky |date=2017 |publisher=[[Springer Science+Business Media|Springer]] |location=New York |isbn=978-3-319-49082-3 |pages=83–89 |url=https://books.google.com/books?id=02DTDgAAQBAJ&q=Messier+71&pg=PA89}}</ref> it was first discovered by the French astronomer [[Philippe Loys de Chéseaux]] in the year 1745 or 1746.<ref name=tt>{{cite book | last1 = Thompson | first1 = Robert Bruce | last2 = Thompson | first2 = Barbara Fritchman | date = 2007 | title = Illustrated Guide to Astronomical Wonders: From Novice to Master Observer | page=394 | url=https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA394 | publisher = [[O'Reilly Media]] | location = North Sebastopol, California | isbn = 978-0-596-52685-6  }}</ref> The loose globular cluster has a mass of around {{solar mass|53,000|link=yes}} and a [[Luminosity#In astronomy|luminosity]] of approximately 19,000 {{lo|link=yes}}.<ref name="Dalgleish">{{cite journal |last1=Dalgleish |first1=H. |last2=Kamann |first2=S. |last3=Usher |first3=C. |last4=Baumgardt |first4=H. |last5=Bastian |first5=N. |last6=Veitch-Michaelis |first6=J. |last7=Bellini |first7=A. |last8=Martocchia |first8=S. |last9=Da Costa |first9=G. S. |last10=Mackey |first10=D. |last11=Bellstedt |first11=S. |last12=Pastorello |first12=N. |last13=Cerulo |first13=P. |title=The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity |journal=Monthly Notices of the Royal Astronomical Society |date=March 2020 |volume=492 |issue=3 |pages=3859–3871 |doi=10.1093/mnras/staa091 |arxiv=2001.01810 |bibcode=2020MNRAS.492.3859D |doi-access=free }}</ref>

There are two notable [[planetary nebula]]e in Sagitta: [[NGC 6886]] is composed of a hot central post-AGB star that has 55% of the Sun's mass yet {{val|2700|850|fmt=commas}} times its luminosity, with a surface temperature of {{val|142000|fmt=commas|u=K}}, and surrounding nebula estimated to have been expanding for between 1,280 and 1,600 years,<ref name=schonberner>{{Cite journal | doi=10.1051/0004-6361/201731788 | bibcode=2018A&A...609A.126S| title=Expansion patterns and parallaxes for planetary nebulae| year=2018| last1=Schönberner| first1=D.| last2=Balick| first2=B.| last3=Jacob| first3=R.| journal=[[Astronomy & Astrophysics]]| volume=609| pages=A126| doi-access=free}}</ref> The nebula was discovered by [[Ralph Copeland]] in 1884.<ref>{{cite web|last=Seligman|first=Courtney|title=NGC Objects: NGC 6850 - 6899|url=http://cseligman.com/text/atlas/ngc68a.htm|access-date=22 August 2015}}</ref> The [[Necklace Nebula]]—originally a close binary, one component of which swallowed the other as it expanded to become a giant star. The smaller star remained in orbit inside the larger, whose rotation speed increased greatly, resulting in it flinging its outer layers off into space, forming a ring with knots of bright gas formed from clumps of stellar material.<ref name=NASANN>{{cite press release |last1=Weaver |first1=Donna |first2=Ray |last2=Villard |date=11 August 2011 |title=Hubble Offers a Dazzling 'Necklace' |url=https://www.nasa.gov/mission_pages/hubble/science/necklace-nebula.html |publisher=NASA |agency=Space Telescope Science Institute |access-date=20 October 2020}}</ref> It was discovered in 2005 and is around 2 light-years wide.<ref name=STSINN>[https://web.archive.org/web/20111014231028/http://hubblesite.org/newscenter/archive/releases/2011/24/image/b/ Hubble Offers a Dazzling View of the 'Necklace' Nebula], news release STScI-2011-24 dated August 11, 2011, from [[Space Telescope Science Institute]]</ref><ref name=NASANN/> It has a size of {{Val|0.35|ul=arcminute}}.<ref name=Sabin2014>{{cite journal | display-authors=1
 | title=First release of the IPHAS catalogue of new extended planetary nebulae
 | last1=Sabin | first1=L. | last2=Parker | first2=Q. A.
 | last3=Corradi | first3=R. L. M. | last4=Guzman-Ramirez | first4=L.
 | last5=Morris | first5=R. A. H. | last6=Zijlstra | first6=A. A.
 | last7=Bojičić | first7=I. S. | last8=Frew | first8=D. J.
 | last9=Guerrero | first9=M. | last10=Stupar | first10=M.
 | last11=Barlow | first11=M. J. | last12=Cortés Mora | first12=F.
 | last13=Drew | first13=J. E. | last14=Greimel | first14=R.
 | last15=Groot | first15=P. | last16=Irwin | first16=J. M.
 | last17=Irwin | first17=M. J. | last18=Mampaso | first18=A.
 | last19=Miszalski | first19=B. | last20=Olguín | first20=L.
 | last21=Phillipps | first21=S. | last22=Santander García | first22=M.
 | last23=Viironen | first23=K. | last24=Wright | first24=N. J.
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=443 | issue=4 | pages=3388–3401 | date=October 2014
 | doi=10.1093/mnras/stu1404 | doi-access=free
 | arxiv=1407.0109
 | bibcode=2014MNRAS.443.3388S }}</ref> Both nebulae are around {{val|15000|fmt=commas|u=light-years}} from Earth.<ref name=schonberner/><ref name=NASANN/>

== See also ==
* [[Sagitta (Chinese astronomy)]]

== Notes ==
{{notelist}}

==References==
{{reflist}}

== External links ==
{{Commons|Sagitta}}
* [http://www.allthesky.com/constellations/vulpecula/ The Deep Photographic Guide to the Constellations: Sagitta]
* [https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017052 Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Sagitta)]
* Bayer's ''[http://lhldigital.lindahall.org/cdm/compoundobject/collection/astro_atlas/id/118/show/41  Uranometria] {{Webarchive|url=https://web.archive.org/web/20201017212847/http://lhldigital.lindahall.org/cdm/compoundobject/collection/astro_atlas/id/118/show/41 |date=2020-10-17 }}'', from the [[Linda Hall Library]] digital collection.

{{Stars of Sagitta}}
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