Editing Alnitak

{{short description|Triple star system in the constellation Orion}}
{{Starbox begin}}
{{Starbox image
| image=[[Image:Star-Alnitak.png|300px]]
| caption=Alnitak between the [[Horsehead Nebula]] and the [[Flame Nebula]]
}}
{{Starbox observe
| epoch=J2000
| ra={{RA|05|40|45.52666}}<ref name=hipparcos>{{cite journal|bibcode=2007A&A...474..653V|title=Validation of the new Hipparcos reduction|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653–664|last1=Van Leeuwen|first1=F.|date=2007|doi=10.1051/0004-6361:20078357|arxiv = 0708.1752 |s2cid=18759600}}</ref>
| dec={{DEC|−01|56|34.2649}}<ref name=hipparcos/>
| appmag_v=1.77<ref name=ducati>{{cite journal|bibcode=2002yCat.2237....0D|title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system|journal=CDS/ADC Collection of Electronic Catalogues|volume=2237|pages=0|last1=Ducati|first1=J. R.|date=2002}}</ref> {{nowrap|(2.08 + 4.28 + 4.01<ref name=hummel/>)}}
| constell=[[Orion (constellation)|Orion]]
| pronounce={{IPAc-en|æ|l|'|n|ai|t|æ|k}},<ref name=Kunitzsch>{{cite book
 |last1=Kunitzsch |first1=Paul
 |last2=Smart |first2=Tim
 |date = 2006 |edition = 2nd rev.
 |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations
 |publisher = Sky Pub |location = Cambridge, Massachusetts
 |isbn = 978-1-931559-44-7
}}</ref>
}}
{{Starbox character
| class=O9.5Iab + B1IV + B0III<ref name=hummel>{{Cite journal | doi = 10.1051/0004-6361/201321434| title = Dynamical mass of the O-type supergiant in ζ Orionis A| journal = Astronomy & Astrophysics| volume = 554| pages = A52| date = 2013| last1 = Hummel | first1 = C. A.| last2 = Rivinius | first2 = T. | last3 = Nieva | first3 = M. -F. | last4 = Stahl | first4 = O.| last5 = Van Belle | first5 = G.| last6 = Zavala | first6 = R. T.|arxiv = 1306.0330 |bibcode = 2013A&A...554A..52H | s2cid = 53645495}}</ref>
| b-v=−0.11 (A)<br />−0.20 (B)<ref name=tycho>{{cite journal|last1=Fabricius|first1=C.|last2=Høg|first2=E.|last3=Makarov|first3=V. V.|last4=Mason|first4=B. D.|last5=Wycoff|first5=G. L.|last6=Urban|first6=S. E.|title=The Tycho double star catalogue|journal=Astronomy and Astrophysics|volume=384|issue=1|date=2002|pages=180–189|issn=0004-6361|doi=10.1051/0004-6361:20011822|bibcode = 2002A&A...384..180F |doi-access=free}}</ref> |
| u-b=−1.06<ref name=ducati/>
| variable=
|type=[[Blue supergiant]] (Aa)}}
{{Starbox astrometry
| radial_v=18.50<ref name="KharchenkoScholz2007">{{cite journal|last1=Kharchenko|first1=N.V.|last2=Scholz|first2=R.-D.|last3=Piskunov|first3=A.E.|last4=Röser|first4=S.|last5=Schilbach|first5=E.|title=Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations|journal=Astronomische Nachrichten|volume=328|issue=9|date=2007|pages=889–896|issn=0004-6337|doi=10.1002/asna.200710776|arxiv = 0705.0878 |bibcode = 2007AN....328..889K |s2cid=119323941}}</ref>
| prop_mo_ra=3.19<ref name=hipparcos/>
| prop_mo_dec=2.03<ref name=hipparcos/>
| parallax=4.43
| p_error=0.64
| parallax_footnote=<ref name=hipparcos/>
| dist_ly={{cvt|387|±|54|pc|ly|disp=number}}
| dist_pc=387 ± 54<ref name=hummel/>
| absmag_v=−6.0 / −3.9 / −4.1<ref name=hummel/>
}}
{{Starbox orbit
| reference = <ref name=hummel/>
| primary = Aa
| name = Ab
| period_unitless = {{val|2,687.3|7.0|fmt=commas|u=d}}
| axis_unitless = {{val|35.9|0.2|ul=mas}}
| eccentricity = {{val|0.338|0.004}}
| inclination = {{val|139.3|0.6}}
| node = {{val|83.8|0.8}}
| periastron = JD {{val|2452734.2|9.0}}
| periarg = {{val|204.2|1.2}}
| k1 = 10.1
| k2 = 19.6
}}
{{Starbox orbit
| reference = <ref name=ORB6>{{cite web|url=https://crf.usno.navy.mil/wds-orb6|title=Sixth Catalog of Orbits of Visual Binary Stars|publisher=United States Naval Observatory}}</ref>
| primary=A
| name=B
| period=1,508.6
| axis=2.728
| eccentricity=0.07
| inclination=72.0
| node=155.5
| periarg=47.3
| periastron=2,070.6
}}
{{Starbox detail
 | component1=Alnitak Aa
 | mass={{val|33|10}}<ref name=hummel/>
 | radius={{val|20.0|3.2}}<ref name=hummel/>
 | luminosity=250,000<ref name=hummel/>
 | gravity = {{val|3.2|0.1}}<ref name=Raassen>{{cite journal|doi=10.1051/0004-6361:20077891|title=XMM-Newton observations of ζ Orionis (O9.7 Ib): A collisional ionization equilibrium model|journal=Astronomy and Astrophysics|volume=478|issue=2|pages=513|year=2008|last1=Raassen|first1=A. J. J.|last2=Van Der Hucht|first2=K. A.|last3=Miller|first3=N. A.|last4=Cassinelli|first4=J. P.|bibcode=2008A&A...478..513R|arxiv = 0803.0873 |s2cid=17601299}}</ref>
 | temperature = {{val|29,500|1,000|fmt=commas}}<ref name=hummel/>
 | rotational_velocity = {{val|110|10}}<ref name=hummel/>
 | rotation = 6.67 days<ref name=brite>{{cite journal|title=Understanding the photometric variability of ζ OriAa|author1=Buysschaert, B.|author2=Neiner, C.|author3=Ramiaramanantsoa, T.|author4=Richardson, N. D.|author5=David-Uraz, A.|author6=Moffat, A. F. J.|journal=Second Brite-Constellation Science Conference: Small Satellites – Big Science|arxiv=1610.05625|date=2016|volume=5|page=101|bibcode=2017sbcs.conf..101B}}</ref>
 | age_myr = 6.4<ref name=hummel/>
 | component2 = Alnitak Ab
 | mass2 = {{val|14|3}}<ref name=hummel/>
 | radius2 = {{val|7.3|1.0}}<ref name=hummel/>
 | luminosity2=32,000<ref name=hummel/>
 | temperature2 = 29,000<ref name=blazere>{{cite journal|bibcode=2015A&A...582A.110B|arxiv=1509.02773|title=The magnetic field of ζ Orionis A|journal=Astronomy & Astrophysics|volume=582|pages=A110|last1=Blazère|first1=A.|last2=Neiner|first2=C.|last3=Tkachenko|first3=A.|last4=Bouret|first4=J.-C.|last5=Rivinius|first5=Th.|year=2015|doi=10.1051/0004-6361/201526855|s2cid=62800990}}</ref>
 | gravirt = 4.0<ref name=blazere/>
 | age_myr2=7.2<ref name=hummel/>
}}
{{Starbox detail | no_heading=y
 | component1=Alnitak B
 | mass=
 | radius=
 | luminosity=
 | temperature=
 | rotational_velocity=350<ref name=hummel/>
 | age_myr=~7<ref name=hummel/>
}}
{{Starbox catalog
| names= {{odlist | B=ζ&nbsp;Orionis | F=50&nbsp;Orionis | name=[[Gould designation|126&nbsp;G.]]&nbsp;Orionis | BD=−02°1338 | SAO=132444 |HIP=26727 | TD1=5127 | WDS=J05407-0157 }}
| component1=A
| names1={{odlist | HR=1948 | HD=37742 }}
| component2=B
| names2={{odlist |HR=1949 | HD=37743 }}
}}
{{Starbox reference
| Simbad=Alnitak | sn=AB
| Simbad2=zet+Ori+A | sn2=A
| Simbad3=zet+Ori+B | sn3=B
}}
{{Starbox end}}

'''Alnitak''' is a triple [[star system]] in the [[constellation]] of [[Orion (constellation)|Orion]]. It has the designations '''ζ Orionis''', which is [[Latinisation of names|Latinised]] to '''Zeta Orionis''' and abbreviated '''Zeta Ori''' or '''ζ Ori''', and '''50 Orionis''', abbreviated '''50 Ori'''. The system is located at a distance of several hundred [[parsec]]s from the [[Sun]] and is one of the three main stars of [[Orion's Belt]] along with [[Alnilam]] and [[Mintaka]].

The primary [[star]], Alnitak Aa, is a hot [[blue supergiant]] with an absolute magnitude of −6.0 and is the brightest [[Stellar classification#Class O|class O]] star in the night sky with a visual magnitude of +2.0. It has two companions—Ab and B, the latter known for the longest time and the former discovered recently, producing a combined magnitude for the trio of +1.77. The stars are members of the [[Orion OB1 association]] and the {{ill|Collinder 70|de|vertical-align=sup}} association.

==Observational history==
[[File:Ngc2024 2mass.jpg|thumb|left|Alnitak (lower right) and the Flame Nebula at [[infrared]] wavelengths]]
Alnitak has been known since antiquity and, as a component of [[#Orion's Belt|Orion's Belt]], has been of widespread cultural significance. It was reported to be a double star by amateur German astronomer [[George K. Kunowsky]] in 1819.<ref name=allen/> Much more recently, in 1998, the bright primary was found by a team from the [[Lowell Observatory]] to have a close companion; this had been suspected from observations made with the [[Narrabri Stellar Intensity Interferometer]] in the 1970s.<ref name="Hummel00"/>

The [[parallax|stellar parallax]] derived from observations by the ''[[Hipparcos]]'' satellite imply a distance around {{val|225|ul=parsecs}}, but this does not take into account distortions caused by the multiple nature of the system.  Larger distances, typically closer to {{val|400|u=pc}},  have been derived by many authors based on the orbit of the pair or the assumed properties of the components.  This distance is comparable to the [[Orion molecular  cloud complex]], including the nearby [[Flame Nebula|Flame]] and [[Horsehead Nebula]]e.<ref name=hummel/>

==Stellar system==
[[Image:Alnitak sun comparison.svg|thumb|left|Alnitak Aa compared to the Sun (to scale)]]
Alnitak is a triple [[star system]] at the eastern end of Orion's Belt, the second-magnitude primary having a 4th-magnitude companion nearly 3 arcseconds distant, in an orbit taking over 1,500 years.

The part called Alnitak A is itself a close binary, comprising the stars Alnitak Aa and Alnitak Ab.

Alnitak Aa is a blue [[supergiant]] of [[spectral type]] O9.5Iab with an [[absolute magnitude]] of −6.0 and an [[apparent magnitude]] of 2.0. It is estimated as being up to 33 times as massive [[Solar mass|as the Sun]] and a diameter 20 times greater. It is some 21,000 times brighter [[Solar luminosity|than the Sun]], with a [[Black body|surface brightness]] ([[luminance]]) some 500 times greater. It is the brightest star of [[Stellar classification#Class O|class O]] in the [[night sky]]. In about a million years, it will expand into a [[red supergiant]] wider than the orbit of [[Jupiter]] before ending its life in a [[supernova]] explosion, likely leaving behind a [[black hole]].

Alnitak Ab is a blue [[subgiant]] of spectral type B1IV with an absolute magnitude of −3.9 and an apparent magnitude of 4.3, discovered in 1998.<ref name="Hummel00">{{cite journal |author=Hummel CA |author2=White NM |author3=Elias NM II |author4=Hajian AR |author5=Nordgren TE|date= 2000|title=ζ Orionis A Is a Double Star |journal=The Astrophysical Journal |volume=540 |issue=2 |pages=L91–L93 |doi=10.1086/312882 |bibcode=2000ApJ...540L..91H|doi-access=free }}</ref>

A fourth star, 9th-magnitude Alnitak C, has not been confirmed to be part of the Aa–Ab–B group, and may simply lie along the line of sight.

The Alnitak system is bathed in the nebulosity of [[IC 434]].

==Etymology and cultural significance==
ζ Orionis ([[Orthographic Latinisation of Greek|Latinised]] as ''Zeta Orionis'') is the star system's [[Bayer designation]] and ''50 Orionis'' its [[Flamsteed designation]].

The traditional name ''Alnitak'', alternately spelled Al Nitak or Alnitah, is taken from the [[Arabic]] النطاق ''an-niṭāq'', "the girdle".<ref name="allen">{{Cite book |last=Allen |first=Richard Hinckley |url=https://archive.org/details/StarNamesAndTheirMeanings |title=Star-names and their meanings |date=1899 |publisher=G.E. Stechert |location=New York, Leipzig |pages=314–15}}</ref> In 2016, the [[International Astronomical Union]] organized a [[Working Group on Star Names]] (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|access-date=22 May 2016}}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}}</ref> included a table of the first two batches of names approved by the WGSN; which included ''Alnitak'' for the star ζ Orionis Aa. It is now so entered in the IAU Catalog of Star Names.<ref name="IAU-CSN">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}}</ref>

===Orion's Belt===
{{Main|Orion's Belt}}
[[File:Orion Belt.jpg|thumb|left|[[Orion's Belt]] with Alnitak on the left]]
The three belt stars were collectively known by many names in many cultures. [[Arabic]] terms include النجاد ''Al Nijād'' 'the Belt', النسك ''Al Nasak'' 'the Line', العلقات ''Al Alkāt'' 'the Golden Grains or Nuts' and, in modern Arabic, ميزان الحق ''Al Mīzān al Ḥaqq'' 'the Scale of Justice'. In [[Chinese mythology]] they were known as The Weighing Beam.<ref name=allen/>

The belt was also the [[Three Stars (Chinese constellation)|Three Stars]] mansion ({{zh|t=參宿|s=参宿|p=Shēn Xiù}}), one of the [[twenty-eight mansions]] of the [[Chinese constellations]]. It is one of the western mansions of the [[White Tiger (Chinese astronomy)|White Tiger]].

In [[Chinese astronomy|Chinese]], {{lang|zh|參宿}} ({{lang|zh-Latn|Shēn Xiù}}), meaning [[Three Stars (Chinese constellation)|Three Stars]] (asterism), refers to an asterism consisting of Alnitak, [[Alnilam]] and [[Mintaka]] (Orion's Belt), with [[Betelgeuse]], [[Bellatrix]], [[Saiph]] and [[Rigel]] later added.<ref>{{in lang|zh}} ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}.</ref> Consequently, the [[Chinese star names|Chinese name]] for Alnitak is {{lang|zh|參宿一}} ({{lang|zh-Latn|Shēn Xiù yī}}, {{langx|en|the First Star of Three Stars}}).<ref>{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0605/ap060525.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 25 日] {{Webarchive|url=https://web.archive.org/web/20110716122642/http://aeea.nmns.edu.tw/2006/0605/ap060525.html |date=2011-07-16 }}</ref> It is one of the western mansions of the [[White Tiger (Chinese astronomy)|White Tiger]].

==Namesakes==
The [[USS Alnitah|USS ''Alnitah'']] was a [[U.S. Navy]] [[Crater-class cargo ship|''Crater''-class cargo ship]] named after the star.
{{clear left}}
==References==
{{Reflist|30em}}

==External links==
* {{cite web |
 title=Alnitak 3 |
 work=SolStation |
 url=http://www.solstation.com/x-objects/alnitak3.htm |
 access-date = 2005-12-15}}
* {{APOD |date=12 January 2010 |title=Image of Alnitak}}
* {{WikiSky}}

{{Stars of Orion}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Sky|05|40|45.5|-|01|56|34|800}}

{{DEFAULTSORT:Alnitak}}
<!-- Properties -->
[[Category:O-type supergiants]]
[[Category:B-type giants]]
[[Category:Triple star systems]]
<!-- Location/catalogues -->
[[Category:Orion (constellation)]]
[[Category:Bayer objects|Orionis, Zeta]]
[[Category:Bright Star Catalogue objects|1948 9]]
[[Category:Durchmusterung objects|BD-02 1338]]
[[Category:Flamsteed objects|Orionis, 50]]
[[Category:Henry Draper Catalogue objects|037742]]
[[Category:Hipparcos objects|026727]]
[[Category:Gould objects|Orionis, 126]]
[[Category:Stars with proper names|Alnitak]]