Editing Equuleus

{{short description|Constellation in the northern celestial hemisphere}}
{{redirects here|Equ|other uses|EQU (disambiguation){{!}}EQU}}
{{Infobox constellation
| name = Equuleus
| abbreviation = Equ
| genitive = Equulei
| pronounce = {{IPAc-en|ᵻ|ˈ|k|w|uː|l|i|ə|s}} ''Equúleus,'' genitive {{IPAc-en|ᵻ|ˈ|k|w|uː|l|i|aɪ}} 
| symbolism = the [[pony]]
| RA = {{RA|20|56|10.9212}}–{{RA|21|26|20.0331}}{{sfn|IAU, ''The Constellations'', Equuleus}}
| dec = {{dec|13.0390635}}–{{dec|2.4773185}}{{sfn|IAU, ''The Constellations'', Equuleus}}
| family = [[Heavenly Waters (astronomy)|Heavenly Waters]]
| quadrant = NQ4
| areatotal = 72
| arearank = 87th
| numbermainstars = 3
| numberbfstars = 10
| numberstarsplanets = 2
| numberbrightstars = 0
| numbernearbystars = 0
| brighteststarname = [[Alpha Equulei|α Equ]] (Kitalpha)
| starmagnitude = 3.92
| neareststarname = [[Gliese 818|HD 200779]]
| stardistancely = 48.41
| stardistancepc = 14.84
| numbermessierobjects = 0
| meteorshowers = 0
| bordering = [[Aquarius (constellation)|Aquarius]]<br />[[Delphinus]]<br />[[Pegasus (constellation)|Pegasus]]
| latmax = [[North Pole|90]]
| latmin = [[80th parallel south|80]]
| month = September
| notes=}}

'''Equuleus''' is a faint [[constellation]] located just north of the [[celestial equator]]. Its name is [[Latin]] for "little horse", a [[foal]]. It was one of the 48 constellations listed by the 2nd century astronomer [[Ptolemy]], and remains one of the 88 modern constellations. It is the second smallest of the modern constellations (after [[Crux]]), spanning only 72 square degrees. It is also very faint, having no stars brighter than the [[apparent magnitude|fourth magnitude]].

==Notable features==
[[Image:EquuleusCC.jpg|thumb|left|256px|The constellation Equuleus as it can be seen by the naked eye.]]

[[Image:Equuleus 20191202.jpg|thumb|right|256px|The constellation Equuleus, color and contrast enhanced.]]

===Stars===
{{see|List of stars in Equuleus}}
The brightest star in Equuleus is [[Alpha Equulei|α Equulei]], traditionally called Kitalpha, a yellow star magnitude 3.9, 186 light-years from Earth. Its traditional name means "the section of the horse".{{sfn|Ridpath|Tirion|2001|pp=144-145}}

There are few [[variable star]]s in Equuleus.  Only around 25 are known, most of which are faint. [[Gamma Equulei|γ Equulei]] is an [[Alpha2 Canum Venaticorum variable|α<sup>2</sup> CVn variable star]], ranging between magnitudes 4.58 and 4.77<ref>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref> over a period of around 12½ minutes.<!-- not cited to Ridpath and Tirion 2001 --> It is a white star 115 light-years from Earth, and has an [[optical binary|optical companion]] of magnitude 6.1, [[6 Equulei]]. It is divisible in binoculars.{{sfn|Ridpath|Tirion|2001|pp=144-145}} 6 Equulei is an astrometric binary system itself,<ref name=Frankowski2007>{{citation | last1=Frankowski | first1=A. | last2=Jancart | first2=S. | last3=Jorissen | first3=A. | title=Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data | journal=Astronomy and Astrophysics | volume=464 | issue=1 | pages=377–392 |date=March 2007 | doi=10.1051/0004-6361:20065526 | bibcode=2007A&A...464..377F |arxiv = astro-ph/0612449 | s2cid=14010423 }}</ref> with an apparent magnitude of 6.07.<ref name=clpl4_99>{{citation | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | year=1966 | page=99 | bibcode=1966CoLPL...4...99J }}</ref> [[R Equulei]] is a [[Mira variable]] that ranges between magnitudes 8.0 and 15.7<ref name=REqu /> over nearly 261 days. It has a spectral type of M3e-M4e<ref name=REqu>{{citation|postscript=.|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|pages=B/gcvs|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref> and has an average B-V colour index of +1.41.<ref name=Zacharias_et_al_2012>{{citation
 | title=The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)
 | display-authors=1 | last1=Zacharias | first1=N.
 | last2=Finch | first2=C. T. | last3=Girard | first3=T. M.
 | last4=Henden | first4=A. | last5=Bartlett | first5=J. L.
 | last6=Monet | first6=D. G. | last7=Zacharias | first7=M. I.
 | journal=VizieR On-line Data Catalog
 | volume=1322 | date=2012 | issue=2 | page=44 | doi=10.1088/0004-6256/145/2/44 | postscript=.
 | bibcode=2012yCat.1322....0Z | arxiv=1212.6182 | s2cid=119299381 }}</ref>

Equuleus contains some [[double star]]s of interest.  γ Equulei consists of a primary star with a magnitude around 4.7 (slightly variable) and a secondary star of magnitude 11.6, separated by 2 [[arcsecond]]s.  [[Epsilon Equulei|ε Equulei]] is a triple star also designated 1 Equulei. The system, 197 light-years away, has a primary of magnitude 5.4 that is itself a binary star; its components are of magnitude 6.0 and 6.3 and have a period of 101 years. The secondary is of magnitude 7.4 and is visible in small telescopes. The components of the primary are becoming closer together and will not be divisible in amateur telescopes beginning in 2015.{{sfn|Ridpath|Tirion|2001|pp=144-145}} [[Delta Equulei|δ Equulei]] is a [[binary star]] with an orbital period of 5.7 years, which at one time was the shortest known orbital period for an optical binary. The two components of the system are never more than 0.35 arcseconds apart.

===Deep-sky objects===
Due to its small size and its distance from the plane of the [[Milky Way]], Equuleus is rather devoid of [[deep sky objects]] such as [[star clusters]] and [[nebulae]]. Some very faint [[galaxy|galaxies]] in the [[New General Catalogue]] between [[Apparent magnitude|magnitudes]] 13 and 15 include [[NGC 7015]], [[NGC 7040]], and [[NGC 7046]]. [[NGC 7045]] is a [[triple star]] that was mistaken as a nebula by its discoverer, [[John Herschel]].<ref>{{Cite web |date= |title=NGC 7045 Basic Information |url=http://ngcicproject.observers.org/NGC/NGC_70xx/NGC_7045.htm |access-date=2024-03-25 |website=The NGC/IC Project}}</ref> Other faint galaxies in the [[Index Catalogue]] include IC 1360, IC 1361, IC 1364, IC 1367, IC 1375, and IC 5083. IC 1365 is a group of galaxies. The magnitudes of these objects vary from 14.5 to 15.5, making them hard to see in even the largest of [[Amateur astronomy|amateur]] telescopes.<ref>{{Cite web |title=Deep sky objects in Equuleus - Full list |url=https://theskylive.com/sky/constellations/equuleus-deepsky-objects |access-date=2024-03-25 |website=The Sky Live}}</ref>

==Mythology==
[[File:Sidney Hall - Urania's Mirror - Pegasus and Equuleus (best currently available version - 2014).jpg|thumb|Seen in ''[[Urania's Mirror]]'' (1825)]]
In [[Greek mythology]], one myth associates Equuleus with the foal Celeris (meaning "swiftness" or "speed"), who was the offspring or brother of the winged horse [[Pegasus]]. Celeris was given to [[Castor and Pollux|Castor]] by [[Mercury (mythology)|Mercury]]. Other myths say that Equuleus is the horse struck from [[Poseidon]]'s trident, during the contest between him and [[Athena]] when deciding which would be the superior. Because this section of stars rises before [[Pegasus]], it is often called Equus Primus, or the First Horse. Equuleus is also linked to the story of [[Philyra (mythology)|Philyra]] and [[Saturn (mythology)|Saturn]].<ref>{{Cite book|last=Olcott|first=William Tyler|url=https://www.worldcat.org/oclc/947036847|title=Star lore of all ages : myths, legends, and facts|date=2004|publisher=Dover Publications|others=Fred Schaaf|isbn=978-0-486-14080-3|edition=Dover|location=Mineola, N.Y.|pages=297|oclc=947036847}}</ref>

Created by [[Hipparchus]] and included by [[Ptolemy]], it abuts Pegasus; unlike the larger horse, it is depicted as a horse's head alone.{{sfn|Ridpath|Tirion|2001|pp=144-145}}
<ref>Evans, James "The History and Practice of Ancient Astronomy" Oxford University Press, 1998.</ref>

==Equivalents==
In [[Chinese astronomy]], the stars that correspond to Equuleus are located within the [[Black Tortoise (Chinese constellation)|Black Tortoise of the North]] (北方玄武, ''Běi Fāng Xuán Wǔ'').<ref>{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0605/ap060515.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 15 日]</ref>

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

==References==
* {{cite web |ref={{sfnRef|IAU, ''The Constellations'', Equuleus}} |title=Equuleus |work=The Constellations |publisher=International Astronomical Union |url=https://www.iau.org/public/themes/constellations/#equ}}
* Burnham, Robert (1978). ''Burnham's Celestial Handbook: An observer's guide to the universe beyond the solar system'', vol 2. Dover Publications {{ISBN|0-486-23567-X}}
* Hoffleit+ (1991) ''V/50 The Bright Star Catalogue'', 5th revised ed, Yale University Observatory, [https://web.archive.org/web/20061012000011/http://cdsweb.u-strasbg.fr/viz-bin/Cat?V%2F50 Strasbourg astronomical Data Center]
* {{citation |title = Stars and Planets Guide |last1 = Ridpath |first1 = Ian |last2 = Tirion |first2 = Wil |year = 2001 |publisher = Princeton University Press |isbn = 0-691-08913-2}}
* Ian Ridpath & Wil Tirion (2007). ''Stars and Planets Guide'', Collins, London. {{ISBN|978-0-00-725120-9}}. Princeton University Press, Princeton. {{ISBN|978-0-691-13556-4}}.
{{reflist}}

== External links ==
{{Commons}}
* [http://www.allthesky.com/constellations/delphinus/ The Deep Photographic Guide to the Constellations: Equuleus]
* [http://astrojan.eu5.org/delphin.htm The clickable Equuleus]
* [http://www.ianridpath.com/startales/equuleus.html Star Tales – Equuleus]
* [https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017055 Warburg Institute Iconographic Database (medieval and early modern images of Equuleus)]

{{Stars of Equuleus}}
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{{DEFAULTSORT:Equuleus Constellation}}
[[Category:Equuleus| ]]
[[Category:Constellations]]
[[Category:Northern constellations]]
[[Category:Constellations listed by Ptolemy]]