View source for Betelgeuse

{{short description|Red supergiant star in the constellation of Orion}}
{{about|the star|the 1988 film|Beetlejuice|other uses}}
{{Featured article}}
{{Use dmy dates|date=October 2019}}
{{Starbox begin
 |name = Betelgeuse
}}
{{Starbox image
 | image =
 {{Location mark
 | image = Orion constellation map.svg | width = 280
 | alt = Map of the constellation Orion | float = center
 | mark = Red circle.svg | mark_width = 15 | mark_link = Betelgeuse (star)
 | x = 449 | y = 310
 }}
 | caption = Location of Betelgeuse (circled)
}}
{{Starbox observe
| epoch = J2000.0
| constell = [[Orion (constellation)|Orion]]
| pronounce = {{IPAc-en|ˈ|b|ɛ|t|əl|dʒ|uː|z|,_|ˈ|b|iː|t|-|,_|-|dʒ|uː|s}} {{respell|BE(E)T|əl|jooz|,_|-|jooss}}<ref name="OED" /><ref name="MWD">{{Cite web |url=http://www.merriam-webster.com/dictionary/betelgeuse |title=Merriam-Webster Dictionary: Betelgeuse |access-date=23 April 2018}}</ref> {{see below|[[#Spelling and pronunciation|below]]}}
| ra = {{RA|05|55|10.30536}}<ref name=hipparcos/>
| dec = {{DEC|+07|24|25.4304}}<ref name=hipparcos/>
| appmag_v = +0.50<ref name="NICOLET" /> {{nowrap|(0.0–1.6<ref name=vsx>{{cite web |title=Alpha Orionis |url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=24710 |website=Variable Star Index |access-date=2020-02-20}}</ref>)}}
}}
{{Starbox character
 | type = [[Red supergiant]]
 | class = M1–M2 Ia–ab<ref name=mk>{{cite journal |last1=Keenan |first1=Philip C. |last2=McNeil |first2=Raymond C. |title=The Perkins catalog of revised MK types for the cooler stars |journal=Astrophysical Journal Supplement Series |volume=71 |pages=245 |year=1989 |bibcode=1989ApJS...71..245K |doi=10.1086/191373|s2cid=123149047 }}</ref>
 | appmag_1_passband = 
 | appmag_1 = 
 | appmag_2_passband = [[J band (infrared)|J]]
 | appmag_2 = −3.00<ref name=ducati>{{cite journal |last=Ducati |first=J.R. |title=VizieR online data catalog: Catalogue of stellar photometry in Johnson's 11&nbsp;color system |journal=CDS/ADC Collection of Electronic Catalogues |volume=2237 |year=2002 |bibcode=2002yCat.2237....0D}}</ref>
 | appmag_3_passband = [[K band (infrared)|K]]
 | appmag_3 = −4.05<ref name=ducati/>
 | b-v = +1.85<ref name="NICOLET">
 {{cite journal |last=Nicolet |first=B. |title=Catalogue of Homogeneous Data in the UBV Photoelectric Photometric System |journal=Astronomy & Astrophysics |volume=34 |pages=1–49 |year=1978 |bibcode=1978A&AS...34....1N}}</ref>
 | u-b = +2.06<ref name="NICOLET" />
 | variable = [[semiregular variable star|SRc]]<ref name=gcvs>
 {{cite journal
 |last1=Samus |first1=N.N.
 |last2=Durlevich |first2=O.V.
 |display-authors=etal
 |year=2009
 |title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)
 |journal=VizieR On-Line Data Catalog: B/gcvs
 |volume=1 |pages=1
 |bibcode=2009yCat....102025S
 }} Originally published in {{bibcode|2009yCat....102025S}}
</ref>
 }}
{{Starbox astrometry
 | radial_v = +21.91<ref>
 {{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.
 |year=2005
 |title=Local kinematics of K and M&nbsp;giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
 |journal=Astronomy and Astrophysics
 |volume=430 |pages=165–186
 |bibcode=2005A&A...430..165F |s2cid=17804304
 |doi=10.1051/0004-6361:20041272 |arxiv=stro-ph/0409579
 }}
</ref>
 | prop_mo_ra = {{val|26.42|0.25}}<ref name=harper2017/>
 | prop_mo_dec = {{val|9.60|0.12}}<ref name=harper2017/>
 | parallax = {{val|5.95|0.58|0.85}}
 | p_error =
 | parallax_footnote =<ref name=joyce2020/>
 | dist_ly = {{val|408}}{{snd}}{{val|548|90|49}}
 | dist_pc = {{val|125}}<ref name=Neuhauser2022/>{{snd}}{{val|168.1|27.5|14.9}}<ref name=joyce2020/>
 | absmag_v = −5.85<ref>
 {{cite journal
 |last1=Lambert |first1=D.L. |last2=Brown |first2=J.A.
 |last3=Hinkle |first3=K.H. |last4=Johnson |first4=H.R.
 |date=September 1984
 |title=Carbon, nitrogen and oxygem abundances in Betelgeuse
 |journal=Astrophysical Journal
 |volume=284 |pages=223–237
 |doi=10.1086/162401 |issn=0004-637X
 |bibcode=1984ApJ...284..223L |language=en
 }}
</ref>
}}
{{Starbox detail
 | mass = 14<ref name=Neuhauser2022/>{{snd}}19<ref name=joyce2020/>
 | radius = ~640<ref name="mittag"/>–{{val|764|116|62}}<ref name=joyce2020/>
 | luminosity = ~65,000<ref name="mittag"/>–{{val|87,100|20,500|11,200|fmt=commas}}<ref name=joyce2020/> 
 | temperature = {{val|3600|200|fmt=commas}}<ref name=joyce2020/>{{snd}}{{val|fmt=commas|3800}}<ref name=Neuhauser2022/>
 | gravity = −0.5<ref name=LOBEL>
 {{cite journal
 | last1=Lobel |first1=Alex
 | last2=Dupree |first2=Andrea K.
 | year=2000
 | title=Modeling the variable chromosphere of {{nobr|{{mvar|α}} Orionis}}
 | journal=The Astrophysical Journal
 | volume=545 | issue=1 | pages=454–74
 | bibcode=2000ApJ...545..454L
 | doi=10.1086/317784 | doi-access=free
 }}
</ref>
 | metal_fe = +0.05<ref name=RAMIREZ>
{{cite journal
 | last1=Ramírez | first1=Solange V.
 | last2=Sellgren | first2=K.
 | last3=Carr | first3=John S.
 | last4=Balachandran | first4=Suchitra C.
 | last5=Blum | first5=Robert
 | last6=Terndrup | first6=Donald M.
 | last7=Steed | first7=Adam
 | title=Stellar iron abundances at the galactic center
 | journal=The Astrophysical Journal
 | date=July 2000
 | volume=537 | issue=1 | pages=205–20
 | bibcode=2000ApJ...537..205R
 | doi=10.1086/309022
 | arxiv=astro-ph/0002062 | s2cid=14713550
 }}
</ref>
 | rotational_velocity = {{val|5.47|0.25}}<ref name=kervella2018/>
 | rotation = {{val|36|8}}<ref name=kervella2018>
{{cite journal
 |bibcode=2018A&A...609A..67K
 |title=The close circumstellar environment of Betelgeuse. V. Rotation velocity and molecular envelope properties from ALMA
 |last1=Kervella |first1=Pierre
 |last2=Decin |first2=Leen
 |last3=Richards |first3=Anita M.S.
 |last4=Harper |first4=Graham M.
 |last5=McDonald |first5=Iain
 |last6=O'Gorman |first6=Eamon
 |last7=Montargès |first7=Miguel
 |last8=Homan |first8=Ward
 |last9=Ohnaka |first9=Keiichi
 |journal=Astronomy and Astrophysics
 |volume=609 |pages=A67 |year=2018
 |arxiv=1711.07983 |doi=10.1051/0004-6361/201731761
 |s2cid=54670700
 }}
</ref> years
 |age_myr = 8.0<ref name=dolan2016>{{cite journal |doi=10.3847/0004-637X/819/1/7 |arxiv=1406.3143v2 |title=Evolutionary Tracks for Betelgeuse |journal=The Astrophysical Journal |volume=819 |issue=1 |pages=7 |year=2017 |last1=Dolan |first1=Michelle M. |last2=Mathews |first2=Grant J. |last3=Lam |first3=Doan Duc |last4=Lan |first4=Nguyen Quynh |last5=Herczeg |first5=Gregory J. |last6=Dearborn |first6=David S.P. |bibcode = 2016ApJ...819....7D |s2cid=37913442 |doi-access=free}}</ref>–14<ref name=Neuhauser2022/>
}}
{{Starbox catalog
 | names=Betelgeuse, [[Bayer designation|{{nobr|{{mvar|α}} Ori}}]], [[Flamsteed designation|58&nbsp;Ori]], [[Harvard Revised catalogue|HR]]&nbsp;2061, [[Bonner Durchmusterung|BD]]+07°1055, [[Henry Draper Catalogue|HD]]&nbsp;39801, [[Catalogues of Fundamental Stars|FK5]]&nbsp;224, [[Hipparcos catalogue|HIP]]&nbsp;27989, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;113271, [[Boss General Catalogue|GC]]&nbsp;7451, [[Catalog of Components of Double and Multiple Stars|CCDM]]&nbsp;J05552+0724, [[American Association of Variable Star Observers|AAVSO]]&nbsp;0549+07
}}
{{Starbox reference
 | Simbad=HD+39801
}}
{{Starbox end}}
{{Sky|05|55|10.3053|+|07|24|25.426|600}}'''Betelgeuse''' is a [[red supergiant]] star in the [[constellation]] of [[Orion (constellation)|Orion]]. It is usually the [[List of brightest stars|tenth-brightest]] [[star]] in the [[night sky]] and, after [[Rigel]], the second brightest in its constellation. It is a distinctly reddish, [[semiregular variable star]] whose [[apparent magnitude]], varying between +0.0 and +1.6, with a main period near 400 days, has the widest range displayed by any [[first-magnitude star]]. Betelgeuse is the brightest star in the night sky at [[near-infrared]] wavelengths. Its [[Bayer designation]] is '''{{nobr|α Orionis}}''', [[Latinisation of names|Latinised]] to '''Alpha Orionis''' and abbreviated '''Alpha&nbsp;Ori''' or '''{{nobr|α Ori}}'''.

With a radius between 640 and 764&nbsp;times that of the Sun,<ref name=mittag>{{cite journal |last1=Mittag |first1=M. |last2=Schröder |first2=K.-P. |last3=Perdelwitz |first3=V. |last4=Jack |first4=D. |last5=Schmitt |first5=J.H.M.M. |date=2023-01-01 |title=Chromospheric activity and photospheric variation of {{nobr|{{mvar|α}} Ori}} during the great dimming event in 2020 |bibcode=2023A&A...669A...9M |journal=[[Astronomy and Astrophysics]] |volume=669 |pages=A9 |doi=10.1051/0004-6361/202244924 |issn=0004-6361|arxiv=2211.04967 }}</ref><ref name=joyce2020/> if it were at the center of the [[Solar System]], its surface would lie beyond the [[asteroid belt]] and it would engulf the [[orbit]]s of [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], and [[Mars]]. Calculations of Betelgeuse's mass range from slightly under ten to a little over twenty times that of the [[Sun]]. For [[#Distance measurements|various reasons]], its distance has been quite difficult to measure; current best estimates are of the order of 400–600&nbsp;[[light-year]]s from the Sun{{snd}}a comparatively wide uncertainty for a relatively nearby star. Its [[absolute magnitude]] is about −6. With an age of less than 10&nbsp;million years, Betelgeuse has evolved rapidly because of its large mass, and is expected to end its evolution with a [[supernova]] explosion, most likely within 100,000&nbsp;years. When Betelgeuse explodes, it will shine as bright as the [[Lunar phase|half-Moon]] for more than three months; life on Earth will be unharmed. Having been ejected from its birthplace in the [[Orion OB1 association]]{{snd}}which includes the stars in [[Orion's Belt]]{{snd}}this [[runaway star]] has been observed to be moving through the [[interstellar medium]] at a speed of {{val|30|u=km/s}}, creating a [[Bow shocks in astrophysics|bow shock]] over four light-years wide.

Betelgeuse became the first extrasolar star whose [[photosphere]]'s angular size was measured in 1920, and subsequent studies have reported an [[angular diameter]] (i.e., apparent size) ranging from 0.042 to 0.056 [[Minute of arc|arcseconds]]; that range of determinations is ascribed to non-sphericity, [[limb darkening]], [[Stellar pulsations|pulsations]] and varying appearance at different [[Electromagnetic radiation|wavelengths]]. It is also surrounded by a complex, asymmetric [[Circumstellar envelope|envelope]], roughly 250&nbsp;times the size of the star, caused by [[Stellar mass loss|mass loss]] from the star itself. The Earth-observed angular diameter of Betelgeuse is exceeded only by those of [[R Doradus]] and the Sun.

Starting in October 2019, Betelgeuse began to dim noticeably, and by mid-February 2020 its brightness had dropped by a factor of approximately 3, from magnitude 0.5 to 1.7. It then returned to a more normal brightness range, reaching a peak of 0.0 visual and 0.1 V-band magnitude in April 2023. Infrared observations found no significant change in [[Bolometric luminosity|luminosity]] over the last 50 years, suggesting that the dimming was due to a change in [[Extinction (astronomy)|extinction]] around the star rather than a more fundamental change. A study using the [[Hubble Space Telescope]] suggests that occluding dust was created by a surface mass ejection; this material was cast millions of miles from the star, and then cooled to form the dust that caused the dimming.

== Nomenclature ==
The star's [[Bayer designation]] is ''{{nobr|{{mvar|α}} Orionis}}'' (Latinised to ''Alpha Orionis''), given by [[Johann Bayer]] in 1603.

The traditional name ''Betelgeuse'' was derived from the [[Arabic language|Arabic]] {{lang|ar|يد الجوزاء}} {{transliteration|ar|Yad al-Jawzā’}} "the hand of ''al-Jawzā’'' [i.e. Orion]".<ref name="ridpath1">{{cite web |url = http://www.ianridpath.com/startales/orion2.html#betelgeuse |last = Ridpath |first = Ian |title = Orion: the meaning of Betelgeuse |access-date =9 September 2021 |work = Star Tales}}</ref><ref name=":0">{{Cite web |title=Definition of BETELGEUSE |url=https://www.merriam-webster.com/dictionary/Betelgeuse |access-date=2023-07-22 |website=www.merriam-webster.com |language=en}}</ref> An error in the 13th-century reading of the Arabic initial ''[[ي|yā’]]'' ({{lang|ar|يـ}}) as ''[[ب|bā’]]'' ({{lang|ar|بـ}}&mdash;a difference in [[Arabic diacritics#I‘jām (phonetic distinctions of consonants)|i‘jām]]) led to the European name.<ref name=":0" /><ref>{{cite magazine |last=Lebling |first=James |title=Arabic in the Sky |url=https://archive.aramcoworld.com/issue/201005/arabic.in.the.sky.htm |magazine=Aramco World |date=September–October 2010 |pages=24–33}}</ref> In English, there are four common pronunciations of this name, depending on whether the first ''e'' is pronounced short or long and whether the ''s'' is pronounced {{IPA|/s/}} or {{IPA|/z/}}:<ref name="OED" /><ref name="MWD"/>
* {{IPAc-en|ˈ|b|ɛ|t|əl|dʒ|uː|z}} {{respell|BET|əl|jooz}};
* {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|z}} {{respell|BEE|təl|jooz}};
* {{IPAc-en|ˈ|b|ɛ|t|əl|dʒ|uː|s}} {{respell|BET|əl|jooss}};
* {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|s}} {{respell|BEE|təl|jooss}}, [[Beetlejuice|popularized for sounding like "beetle juice"]].

In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name=WGSN>{{cite web
 | title=IAU Working Group on Star Names (WGSN)
 | publisher=[[International Astronomical Union]] (IAU)
 | url=https://www.iau.org/science/scientific_bodies/working_groups/280/
 | access-date=22 May 2016
 | archive-date=10 June 2016
 | archive-url=https://web.archive.org/web/20160610172014/https://www.iau.org/science/scientific_bodies/working_groups/280/
 | url-status=dead
 }}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin, issued July 2016,<ref name=WGSN1>
{{cite web
 | title=Bulletin of the IAU Working Group on Star Names
 | volume=1
 | publisher=[[International Astronomical Union]] (IAU)
 | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf
 | access-date=28 July 2016
 | via=[[University of Rochester]]
}}
</ref> included a table of the first two batches of names approved by the WGSN, which included ''Betelgeuse'' for this star. It is now so entered in the [[IAU Working Group on Star Names|IAU Catalog of Star Names]].<ref name=IAU-CSN>
{{cite web
 | title=IAU Catalog of Star Names
 | department=IAU Division&nbsp;C, Working Group on Star Names (WGSN)
 | publisher=[[International Astronomical Union]] (IAU)
 | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt
 | access-date=28 July 2016
 | via=[[University of Rochester]]
}}</ref>

== Observational history ==
Betelgeuse and its red coloration have been noted since [[Classical antiquity|antiquity]]; the classical astronomer [[Ptolemy]] described its color as {{Transliteration|grc|hypókirrhos}} ({{wikt-lang|grc|ὑπόκιρρος}}, 'more or less orange-tawny'), a term later described by a translator of [[Ulugh Beg]]'s ''[[Zij-i Sultani]]'' as {{wikt-lang|la|rubedo}}, [[Latin]] for 'ruddiness'.<ref name=allen/>{{efn|
''Stella lucida in umero dextro, quae ad rubedinem vergit.''<ref name=allen/>
:
"Bright star in right shoulder, which inclines to ruddiness."
}} In the 19th century, before modern systems of [[stellar classification]], [[Angelo Secchi]] included Betelgeuse as one of the prototypes for his [[Secchi classes|Class&nbsp;III]] (orange to red) stars.<ref>
{{cite conference
 | last=Brück | first=H. A.
 | date=11–15 July 1978
 | title=P. Angelo Secchi, S.J. 1818–1878
 | conference=Spectral Classification of the Future
 | editor1-last=McCarthy | editor1-first=M.F. 
 | editor2-last=Philip | editor2-first=A.G.D.
 | editor3-last=Coyne | editor3-first=G.V. 
 | book-title=Proceedings of the IAU Colloquium&nbsp;47
 | pages=7–20
 | publication-date=1979
 | location=Vatican City, IT
 | bibcode=1979RA......9....7B
}}</ref> Three centuries before Ptolemy, in contrast, Chinese astronomers observed Betelgeuse as yellow; such an observation, if accurate, could suggest the star was in a [[yellow supergiant]] phase around this time,<ref name=NEWSCIENTIST1>{{cite magazine
 | title=Ancient Chinese suggest Betelgeuse is a young star
 | date=22 October 1981
 | via=Reed Business Information
 | magazine=[[New Scientist]]
 | volume=92
 | issue=1276
 | page=238
 | url=https://books.google.com/books?id=L4NTyHivbV8C&pg=PA238
 }}{{Dead link|date=April 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name=Neuhauser2022>{{Cite journal |last1=Neuhäuser |first1=R |last2=Torres |first2=G |last3=Mugrauer |first3=M |last4=Neuhäuser |first4=D L |last5=Chapman |first5=J |last6=Luge |first6=D |last7=Cosci |first7=M |date=October 2022 |title=Colour evolution of Betelgeuse and Antares over two millennia, derived from historical records, as a new constraint on mass and age |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=516 |issue=1 |pages=693–719 |bibcode=2022MNRAS.516..693N |doi=10.1093/mnras/stac1969 |issn=0035-8711 |doi-access=free |arxiv=2207.04702 |hdl-access=free |hdl=10278/5003332}}</ref> a credible possibility, given current research into these stars' complex circumstellar environment.<ref name=LEVESQUE1/>

=== Nascent discoveries ===
Aboriginal groups in South Australia have shared oral tales of the variable brightness of Betelgeuse for an unknown period.<ref>
{{cite news
 |last1=Boutsalis |first1=Kelly
 |date=10 August 2020
 |title=Teaching indigenous star stories
 |website=The Walrus
 |url=https://thewalrus.ca/space-teaching-indigenous-star-stories/
 |access-date=6 July 2021
}}
</ref><ref>
{{cite journal
 |last1=Hamacher |first1=Duane W.
 |year=2018
 |title=Observations of red-giant variable stars by Aboriginal Australians
 |journal=[[The Australian Journal of Anthropology]]
 |volume=29 |page=89
 |doi=10.1111/taja.12257 |arxiv=1709.04634
 |s2cid=119453488 |bibcode=2018AuJAn..29...89H
}}
</ref>

[[File:John Herschel 1846 (cropped).png|thumb|left|upright=0.8| [[John Herschel|Sir&nbsp;John Herschel]] in 1846]]
The variation in Betelgeuse's brightness was described in 1836 by [[John Herschel|Sir John Herschel]] in ''Outlines of Astronomy''. From 1836 to 1840, he noticed significant changes in magnitude when Betelgeuse outshone [[Rigel]] in October 1837 and again in November 1839.<ref name=wilk99/> A 10-year quiescent period followed; then in 1849, Herschel noted another short cycle of variability, which peaked in 1852. Later observers recorded unusually high [[Maxima and minima|maxima]] with an interval of years, but only small variations from 1957 to 1967. The records of the [[American Association of Variable Star Observers]] (AAVSO) show a maximum [[apparent magnitude|brightness]] of 0.2 in 1933 and 1942, and a minimum of 1.2, observed in 1927 and 1941.<ref name="AAVSO">
{{cite web
 | last=Davis |first=Kate
 | date=December 2000
 | title=Variable star of the month: Alpha Orionis
 | publisher=[[American Association of Variable Star Observers]] (AAVSO)
 | url=http://www.aavso.org/vsots_alphaori
 | access-date=10 July 2010
}}
</ref><ref name=BURNHAM>
{{cite book
 | first=Robert Jr. | last=Burnham | author-link=Robert Burnham Jr.
 | year=1978
 | title=Burnham's Celestial Handbook: An observer's guide to the universe beyond the Solar system
 | volume=2
 | publisher=Courier Dover Publications
 | location=New York, NY
 | isbn=978-0-486-23568-4
 | url=https://archive.org/details/burnhamscelestia02robe
 | url-access=registration
 | page=[https://archive.org/details/burnhamscelestia02robe/page/1290 1290]
}}
</ref> This variability in brightness may explain why [[Johann Bayer]], with the publication of his ''[[Uranometria]]'' in 1603, designated the star ''alpha'', as it probably rivaled the usually brighter Rigel (''beta'').<ref name="100greatest">
{{cite book
 | last=Kaler |first= James B.
 | year=2002
 | title=The Hundred Greatest Stars
 | publisher=Copernicus Books
 | location=New York, NY
 | isbn=978-0-387-95436-3
 | page=33
}}
</ref> From Arctic latitudes, Betelgeuse's red colour and higher location in the sky than Rigel meant the [[Inuit]] regarded it as brighter, and one local name was ''Ulluriajjuaq'' ("large star").<ref name=inuit>
{{cite book
 |last = MacDonald |first = John
 |year = 1998
 |title = The Arctic sky: Inuit astronomy, star lore, and legend
 |publisher = Royal Ontario Museum / Nunavut Research Institute
 |location = Toronto, Ontario / Iqaluit, NWT
 |isbn = 978-0-88854-427-8
 |url = https://archive.org/details/arcticskyinuitas0000macd/page/52
 |url-access = registration
 |pages = [https://archive.org/details/arcticskyinuitas0000macd/page/52 52–54, 119]
}}
</ref>

In 1920, [[Albert A. Michelson]] and [[Francis G. Pease]] mounted a six-meter [[Interferometry|interferometer]] on the front of the 2.5-meter telescope at [[Mount Wilson Observatory]], helped by [[John August Anderson]]. The trio measured the angular diameter of Betelgeuse at 0.047[[arcsecond|″]], a figure that resulted in a diameter of {{val|3.84|e=8|u=km}} ({{val|2.58|ul=AU}}) based on the [[stellar parallax|parallax]] value of {{val|0.018|ul="}}.<ref name=MICHELSON>
{{cite journal
 |last1=Michelson |first1=A.A. |author1-link=Albert Abraham Michelson
 |last2=Pease |first2=F.G. |author2-link=Francis G. Pease
 |year=1921
 |title=Measurement of the diameter of Alpha Orionis with the interferometer
 |journal=[[Astrophysical Journal]]
 |volume=53 |issue=5 |pages=249–259
 |bibcode=1921ApJ....53..249M
 |doi=10.1086/142603 |pmid=16586823
 |pmc=1084808 |s2cid=21969744
|quote=The 0.047&nbsp;arcsecond measurement was for a uniform disk. In the article Michelson notes that limb darkening would increase the angular diameter by about 17%, hence 0.055&nbsp;arcseconds.
}}
</ref> But limb darkening and measurement errors resulted in uncertainty about the accuracy of these measurements.

The 1950s and 1960s saw two developments that affected stellar [[convection]] theory in red supergiants: the [[Stratoscope]] projects and the 1958 publication of ''Structure and Evolution of the Stars'', principally the work of [[Martin Schwarzschild]] and his colleague at [[Princeton University]], Richard Härm.<ref name=BRUCEMEDAL>
{{cite web
 | last=Tenn |first = Joseph S.
 | date=June 2009
 | title=Martin Schwarzschild 1965
 | series=The Bruce Medalists
 | publisher=[[Astronomical Society of the Pacific]] (ASP)
 | url=http://www.phys-astro.sonoma.edu/BruceMedalists/
 | access-date=28 September 2010
}}
</ref><ref name=SCHWARZSCHILD1958>
{{cite book
 | last=Schwarzschild |first=M. |author-link=Martin Schwarzschild
 | year=1958
 | title=Structure and Evolution of the Stars
 | publisher=Princeton University Press
 | bibcode=1958ses..book.....S
 | isbn=978-0-486-61479-3
 | url=https://archive.org/details/StructureAndEvolutionOfTheStars
 | url-access=registration
}}
</ref>
This book disseminated ideas on how to apply computer technologies to create stellar models, while the Stratoscope projects, by taking balloon-borne telescopes above the Earth's [[Wave turbulence|turbulence]], produced some of the finest images of [[solar granule]]s and [[sunspot]]s ever seen, thus confirming the existence of convection in the solar atmosphere.<ref name=BRUCEMEDAL/>
{{clear}}

=== Imaging breakthroughs ===
[[File:Betelgeuse pulsating UV (HST).jpg|thumb|right|1998/9 [[ultraviolet|UV]] [[Hubble Space Telescope|HST]] images of Betelgeuse showing asymmetrical pulsations with corresponding [[spectral line]] profiles]]
Astronomers saw some major advances in astronomical imaging technology in the 1970s, beginning with [[Antoine Émile Henry Labeyrie|Antoine Labeyrie]]'s invention of [[speckle interferometry]], a process that significantly reduced the blurring effect caused by [[astronomical seeing]]. It increased the [[optical resolution]] of ground-based [[telescope]]s, allowing for more precise measurements of Betelgeuse's photosphere.<ref name=LABEYRIE1970>
{{cite journal
 | last=Labeyrie |first=A. | author-link=Antoine Émile Henry Labeyrie
 | date=May 1970
 | title=Attainment of diffraction-limited resolution in large telescopes by Fourier analysing speckle patterns in star images
 | journal=[[Astronomy and Astrophysics]]
 | volume=6 | page=85
 | bibcode=1970A&A.....6...85L
}}
</ref><ref name=BONNEAU1973>
{{cite journal
 | last1=Bonneau |first1=D.
 | last2=Labeyrie |first2=A. | author2-link=Antoine Émile Henry Labeyrie
 | year=1973
 | title=Speckle interferometry: Color-dependent limb darkening evidenced on Alpha Orionis and Omicron Ceti
 | journal=[[Astrophysical Journal]]
 | volume= 181 | page=L1
 | bibcode=1973ApJ...181L...1B
 | doi=10.1086/181171
}}
</ref> With improvements in [[infrared telescopy]] atop [[Mount Wilson Observatory|Mount Wilson]], [[McDonald Observatory|Mount Locke]], and [[Mauna Kea Observatories|Mauna Kea]] in Hawaii, astrophysicists began peering into the complex circumstellar shells surrounding the supergiant,<ref name=SUTTON1977>
{{cite journal
 | last1=Sutton |first1=E.C. | last2=Storey |first2=J.W.V.
 | last3=Betz |first3=A.L. | last4=Townes |first4=C.H.
 | last5=Spears |first5=D.L.
 | year=1977
 | title=Spatial heterodyne tnterferometry of VY&nbsp;Canis Majoris, Alpha Orionis, Alpha Scorpii, and R&nbsp;Leonis at 11&nbsp;microns
 | journal=[[Astrophysical Journal Letters]]
 | volume=217 | pages=L97–L100
 | doi=10.1086/182547 | bibcode=1977ApJ...217L..97S
| doi-access=free
 }}
</ref><ref name=BERNAT1975>
{{cite journal
 | last1=Bernat |first1=A.P.
 | last2=Lambert |first2=D.L.
 | date=November 1975
 | title=Observations of the circumstellar gas shells around Betelgeuse and Antares
 | journal=[[Astrophysical Journal]]
 | volume=201 | pages=L153–L156
 | doi=10.1086/181964 | bibcode=1975ApJ...201L.153B
| doi-access=free
 }}
</ref><ref name=DYCK1975>
{{cite journal
 | last1=Dyck |first1=H.M.
 | last2=Simon |first2=T.
 | date=February 1975
 | title=Circumstellar dust shell models for Alpha Orionis
 | journal=[[Astrophysical Journal]]
 | volume=195 | pages=689–693
 | doi=10.1086/153369 | bibcode=1975ApJ...195..689D
}}
</ref> causing them to suspect the presence of huge gas bubbles resulting from convection.<ref name=BOESGAARD1975>
{{cite journal
 | last1=Boesgaard |first1=A.M.
 | last2=Magnan |first2=C.
 | date=June 1975
 | title=The circumstellar shell of alpha Orionis from a study of the Fe&nbsp;II emission lines
 | journal=[[Astrophysical Journal]]
 | volume=198 | issue=1 | pages=369–371, 373–378
 | doi=10.1086/153612 | bibcode=1975ApJ...198..369B
}}
</ref> However, it was not until the late 1980s and early 1990s, when Betelgeuse became a regular target for [[aperture masking interferometry]], that breakthroughs occurred in visible-light and [[Infrared photography|infrared imaging]]. Pioneered by [[John E. Baldwin|J.E.&nbsp;Baldwin]] and colleagues of the [[Cavendish Astrophysics Group]], the new technique employed a small mask with several holes in the telescope pupil plane, converting the [[aperture]] into an ad hoc interferometric array.<ref name=BERNAT2008>
{{cite web
 | last=Bernat |first=David
 | year=2008
 | title=Aperture masking interferometry
 | website=Ask an Astronomer
 | publisher=[[Cornell University]]
 | series=Astronomy department
 | url=http://astro.cornell.edu/~dbernat/apm.html#
 | access-date=15 October 2012
}}
</ref> The technique contributed some of the most accurate measurements of Betelgeuse while revealing bright spots on the star's photosphere.<ref name=BUSCHER>
{{cite journal
 | last1=Buscher |first1=D.F. | last2=Baldwin |first2=J.E.
 | last3=Warner |first3=P.J. | last4=Haniff |first4=C.A.
 | year=1990
 | title=Detection of a bright feature on the surface of Betelgeuse
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=245 | page=7
 | bibcode=1990MNRAS.245P...7B
}}
</ref><ref name=WILSON1>
{{cite journal
 | last1=Wilson |first1=R.W.
 | last2=Dhillon |first2=V.S.
 | last3=Haniff |first3=C.A.
 | year=1997
 | title=The changing face of Betelgeuse
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=291 | issue=4 | page=819
 | bibcode=1997MNRAS.291..819W
 | doi=10.1093/mnras/291.4.819 | doi-access=free
 }}
</ref><ref name=BURNS>
{{cite journal
 | last1=Burns | first1=D. | last2=Baldwin | first2=J.E.
 | last3=Boysen | first3=R.C. | last4=Haniff | first4=C.A.
 | last5=Lawson | first5=P.R. | last6=MacKay | first6=C.D.
 | last7=Rogers | first7=J. | last8=Scott | first8=T.R.
 | last9=Warner | first9=P.J.
 | display-authors=6
 | date=September 1997
 | title=The surface structure and limb-darkening profile of Betelgeuse
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=290 | issue=1 | pages=L11–L16
 | bibcode=1997MNRAS.290L..11B
 | doi=10.1093/mnras/290.1.l11 | doi-access=free
}}
</ref> These were the first optical and infrared images of a stellar disk other than the [[Sun]], taken first from ground-based interferometers and later from higher-resolution observations of the [[Cambridge Optical Aperture Synthesis Telescope|COAST telescope]]. The "bright patches" or "hotspots" observed with these instruments appeared to corroborate a theory put forth by Schwarzschild decades earlier of massive [[Convection zone|convection]] cells dominating the stellar surface.<ref name=TUTHILL>
{{cite journal
 | last1=Tuthill | first1=P.G.
 | last2=Haniff | first2=C.A.
 | last3=Baldwin | first3=J.E.
 | date=March 1997
 | title=Hotspots on late-type supergiants
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=285 | issue=3 | pages=529–39
 | bibcode=1997MNRAS.285..529T
 | doi=10.1093/mnras/285.3.529 | doi-access=free
}}
</ref><ref name=SCHWARZSCHILD1975>
{{cite journal
 | last=Schwarzschild | first=M. |author-link=Martin Schwarzschild
 | year=1975
 | title=On the scale of photospheric convection in red giants and supergiants
 | journal=[[Astrophysical Journal]]
 | volume=195 | issue=1 | pages=137–44
 | bibcode=1975ApJ...195..137S | doi=10.1086/153313
| doi-access=free}}
</ref>

In 1995, the [[Hubble Space Telescope]]'s [[Faint Object Camera]] captured an [[Ultraviolet astronomy|ultraviolet image]] with a resolution superior to that obtained by ground-based interferometers—the first conventional-telescope image (or "direct-image" in NASA terminology) of the disk of another star.<ref name=GILLILAND1>
{{cite journal
 | last1=Gilliland | first1=Ronald L.
 | last2=Dupree | first2=Andrea K.
 | date=May 1996
 | title=First image of the surface of a star with the Hubble Space Telescope
 | journal=[[Astrophysical Journal Letters]]
 | volume=463 | issue=1 | pages=L29
 | bibcode=1996ApJ...463L..29G
 | doi=10.1086/310043 | doi-access=free
 | quote=The yellow/red "image" or "photo" of Betelgeuse commonly seen is not a picture of the red supergiant, but a mathematically generated image based on the photograph. The photograph was of much lower resolution: The entire Betelgeuse image fit within a 10×10 pixel area on the [[Hubble Space Telescope]]s [[Faint Object Camera]]. The images were oversampled by a factor of 5 with bicubic spline interpolation, then deconvolved.
}}
</ref>
Because [[ultraviolet]] light is absorbed by the [[Atmosphere of Earth|Earth's atmosphere]], observations at these wavelengths are best performed by [[space telescope]]s.<ref name=cox2000>
{{cite book
 | editor=Cox, A.N.
 | title=Allen's Astrophysical Quantities
 | year=2000
 | publisher=Springer-Verlag
 | location=New York, NY
 | isbn=978-0-387-98746-0
}}
</ref>
This image, like earlier pictures, contained a bright patch indicating a region in the southwestern quadrant {{val|2000|ul=K|fmt=commas}} hotter than the stellar surface.<ref>
{{cite book
 | last1=Petersen | first1=Carolyn Collins
 | last2=Brandt | first2=John C.
 | year=1998 | orig-year=1995
 | title=Hubble Vision: Further adventures with the Hubble Space Telescope | edition=2nd
 | publisher=Cambridge University Press
 | location=Cambridge, UK
 | isbn=978-0-521-59291-8
 | url=https://archive.org/details/hubblevisionfurt0000pete
 | url-access=registration
 | pages=[https://archive.org/details/hubblevisionfurt0000pete/page/91 91–92]
}}
</ref>
Subsequent ultraviolet spectra taken with the [[Goddard High Resolution Spectrograph]] suggested that the hot spot was one of Betelgeuse's poles of rotation. This would give the rotational axis an inclination of about 20° to the direction of Earth, and a [[position angle]] from [[Celestial pole|celestial North]] of about 55°.<ref name=UITENBROEK>
{{cite journal
 | last1=Uitenbroek | first1=Han
 | last2=Dupree | first2=Andrea K.
 | last3=Gilliland | first3=Ronald L.
 | year=1998
 | title=Spatially resolved Hubble Space Telescope spectra of the chromosphere of {{nobr|{{mvar|α}} Orionis}}
 | journal=The Astronomical Journal
 | volume=116 | issue=5 | pages=2501–2512
 | doi=10.1086/300596 | bibcode=1998AJ....116.2501U
 | s2cid=117596395
| doi-access=free
 }}
</ref>

=== 2000s studies ===
In a study published in December 2000, the star's diameter was measured with the [[Infrared Spatial Interferometer]] (ISI) at mid-infrared wavelengths producing a limb-darkened estimate of {{val|55.2|0.5|ul=mas}} – a figure entirely consistent with Michelson's findings eighty years earlier.<ref name=MICHELSON/><ref name=WEINER>
{{cite journal
 | last1=Weiner | first1 = J. | last2=Danchi | first2=W.C.
 | last3=Hale | first3=D.D.S. | last4=McMahon | first4=J.
 | last5=Townes | first5=C.H. | last6=Monnier | first6=J.D.
 | last7=Tuthill | first7=P.G.
 | date=December 2000
 | title=Precision measurements of the diameters of {{nobr|{{mvar|α}} Orionis}} and ο&nbsp;Ceti at 11&nbsp;microns
 | journal=The Astrophysical Journal
 | volume=544 | issue=2 | pages=1097–1100
 | bibcode=2000ApJ...544.1097W
 | doi=10.1086/317264 | doi-access=free
}}
</ref>
At the time of its publication, the estimated parallax from the [[Hipparcos]] mission was {{val|7.63|1.64|u=mas}}, yielding an estimated radius for Betelgeuse of {{val|3.6|u=AU}}. However, an infrared interferometric study published in 2009 announced that the star had shrunk by 15% since 1993 at an increasing rate without a significant diminution in magnitude.<ref name=UCBERKELEY2009>
{{cite press release
 | last=Sanders | first=Robert
 | date=9 June 2009
 | title=Red giant star Betelgeuse mysteriously shrinking
 | website=UC Berkeley News
 | publisher=UC Berkeley
 | url=http://www.berkeley.edu/news/media/releases/2009/06/09_betelim.shtml
 | access-date=18 April 2010
}}
</ref><ref name=TOWNES1/>
Subsequent observations suggest that the apparent contraction may be due to shell activity in the star's extended atmosphere.<ref name=RAVI1>
{{cite journal
 | last1=Ravi | first1=V. | last2=Wishnow | first2=E.
 | last3=Lockwood | first3=S. | last4=Townes | first4=C.
 | date=December 2011
 | title=The many faces of Betelgeuse
 | journal=[[Publications of the Astronomical Society of the Pacific]]
 | volume=448 | page=1025
 | bibcode=2011ASPC..448.1025R | arxiv = 1012.0377
}}
</ref>

In addition to the star's diameter, questions have arisen about the complex dynamics of Betelgeuse's extended atmosphere. The mass that makes up galaxies is recycled as [[life cycle of stars|stars are formed and destroyed]], and red supergiants are major contributors, yet the process by which mass is lost remains a mystery.<ref name=BERNAT>
{{cite journal
 | last=Bernat | first=Andrew P.
 | year=1977
 | title=The circumstellar shells and mass-loss rates of four M&nbsp;supergiants
 | journal=[[Astrophysical Journal]]
 | volume=213 | pages=756–66
 | bibcode=1977ApJ...213..756B | doi=10.1086/155205
 | s2cid=121146305
 }}
</ref>
With advances in interferometric methodologies, astronomers may be close to resolving this conundrum. Images released by the [[European Southern Observatory]] in July 2009, taken by the ground-based [[Very Large Telescope]] Interferometer (VLTI), showed a vast plume of gas extending {{val|30|u=AU}} from the star into the surrounding atmosphere.<ref name=KERVELLA2009>
{{cite journal
 | last1=Kervella | first1=P. | last2=Verhoelst | first2=T.
 | last3=Ridgway | first3=S.T. | last4=Perrin | first4=G.
 | last5=Lacour | first5=S. | last6=Cami | first6=J.
 | last7=Haubois | first7=X.
 | date=September 2009
 | title=The close circumstellar environment of Betelgeuse. Adaptive optics spectro-imaging in the near-IR with VLT/NACO
 | journal=Astronomy and Astrophysics
 | volume=504 | issue=1 | pages=115–25
 | bibcode=2009A&A...504..115K | s2cid=14278046
 | doi=10.1051/0004-6361/200912521 |arxiv = 0907.1843
}}
</ref>
This mass ejection was equal to the distance between the Sun and [[Neptune]] and is one of multiple events occurring in Betelgeuse's surrounding atmosphere. Astronomers have identified at least six shells surrounding Betelgeuse. Solving the mystery of mass loss in the late stages of a star's evolution may reveal those factors that precipitate the explosive deaths of these stellar giants.<ref name="UCBERKELEY2009" />

===2019–2020 fading===
[[File:Betelgeuse AAVSO 2019.jpg|thumb|upright=1.4|[[AAVSO]] [[apparent magnitude|V-band magnitude]] of Betelgeuse, between September&nbsp;2016 and August&nbsp;2023]]
[[File:Eso2003c.jpg|thumb|upright=1.4|alt=Two orange blobs side by side on black backgrounds, one caption "Jan&nbsp;2019" and the other captioned "Dec&nbsp;2019"|Comparison of [[SPHERE]] images of Betelgeuse taken in January&nbsp;2019 and December&nbsp;2019, showing the changes in brightness and shape]]

A pulsating [[semiregular variable star]], Betelgeuse is subject to multiple cycles of increasing and decreasing brightness due to changes in its size and temperature.<ref name=dolan2016/> The astronomers who first noted the dimming of Betelgeuse, [[Villanova University]] astronomers Richard Wasatonic and [[Edward Guinan]], and amateur Thomas Calderwood, theorize that a coincidence of a normal 5.9&nbsp;year light-cycle minimum and a deeper-than-normal 425&nbsp;day period are the driving factors.<ref name=AT-20191223>
{{cite news
 |last1=Guinan |first1=Edward F. |author1-link = Edward Guinan
 |last2=Wasatonic |first2=Richard J.
 |last3=Calderwood |first3=Thomas J.
 |date=23 December 2019
 |title=Updates on the "fainting" of Betelgeuse
 |website=[[The Astronomer's Telegram]]
 |id=ATel #13365
 |url=http://www.astronomerstelegram.org/?read=13365
 |access-date=27 December 2019
}}
</ref>
Other possible causes hypothesized by late 2019 were an eruption of gas or dust or fluctuations in the star's surface brightness.<ref name=earthsky>
{{cite web
 |first=Deborah |last=Byrd
 |date=2019-12-23 
 |title=Betelgeuse is 'fainting' but (probably) not about to explode
 |website=Earth & Sky
 |url=https://earthsky.org/space/betelgeuse-fainting-probably-not-about-to-explode
 |access-date=2020-01-04 |df=dmy-all
}}
</ref>

By August&nbsp;2020, long-term and extensive studies of Betelgeuse, primarily using [[Ultraviolet astronomy|ultraviolet observations]] by the [[Hubble Space Telescope]], had suggested that the unexpected dimming was probably caused by an immense amount of superhot material ejected into space. The material cooled and formed a dust cloud that blocked the starlight coming from about a quarter of Betelgeuse's surface. Hubble captured signs of dense, heated material moving through the star's atmosphere in September, October and November before several telescopes observed the more marked dimming in December and the first few months of 2020.<ref name=NYT-20200814>
{{cite news
 |last=Overbye |first=Dennis |author-link=Dennis Overbye
 |date=14 August 2020
 |title=This star looked like it would explode. Maybe it just sneezed
 |newspaper=[[The New York Times]]
 |url=https://www.nytimes.com/2020/08/14/science/betelgeuse-star-supernova.html
 |access-date=15 August 2020
 |quote=The mysterious dimming of the red supergiant Betelgeuse is the result of a stellar exhalation, astronomers say.
}}
</ref><ref>
{{cite press release
 |title=Hubble finds that Betegeuse's mysterious dimming is due to a traumatic outburst
 |date=13 August 2020 
 |publisher=[[Hubble Space Telescope]]
 |url=https://hubblesite.org/contents/news-releases/2020/news-2020-44
}}
</ref><ref name=APJ-20200813>
{{cite journal 
 |last1=Dupree | first1=Adrea K. 
 |display-authors=etal 
 |date=13 August 2020 
 |title=Spatially resolved ultraviolet spectroscopy of the great dimming of Betelgeuse 
 |journal=[[The Astrophysical Journal]]
 |volume=899 |number=1 |page=68
 |doi=10.3847/1538-4357/aba516 |arxiv=2008.04945
 |bibcode=2020ApJ...899...68D |s2cid=221103735
|doi-access=free 
 }}
</ref>

By January&nbsp;2020, Betelgeuse had dimmed by a factor of approximately 2.5 from magnitude&nbsp;0.5 to 1.5 and was reported still fainter in February in ''[[The Astronomer's Telegram]]'' at a record minimum of +1.614, noting that the star is currently the "least luminous and coolest" in the 25&nbsp;years of their studies and also calculating a decrease in radius.<ref name=AT-20200201>
{{cite news
 |last1=Guinan |first1=Edward F.
 |last2=Wasatonic |first2=Richard J.
 |date=1 February 2020
 |title=Betelgeuse Updates – 1 February 2020; 23:20 UT
 |id=ATel #13439
 |website=[[The Astronomer's Telegram]]
 |url=http://www.astronomerstelegram.org/?read=13439
 |access-date=2 February 2020
}}
</ref>
''[[Astronomy (magazine)|Astronomy]]'' magazine described it as a "bizarre dimming",<ref name = Dec2019-AstroMag>
{{cite news
 |first = Erika K. |last = Carlson
 |date = 27 December 2019
 |title = Betelguese's bizarre dimming has astronomers scratching their heads
 |magazine = [[Astronomy (magazine)|Astronomy]]
 |url = http://www.astronomy.com/news/2019/12/betelgueses-bizarre-dimming-has-astronomers-scratching-their-heads
 |access-date = 28 December 2019
}}
</ref>
and popular speculation inferred that this might indicate an imminent [[supernova]].<ref>
{{cite news
 |last=Griffin |first=Andrew
 |date= 29 December 2019
 |title=Betelgeuse: Star is behaving strangely and could be about to explode into a supernova, say astronomers
 |newspaper=[[The Independent]]
 |url=https://www.independent.co.uk/life-style/gadgets-and-tech/news/betelgeuse-star-night-sky-supernova-explosion-a9263626.html
 |access-date=2019-12-30 |df=dmy-all
}}
</ref><ref>
{{cite news
 |last=Mack |first=Erick 
 |date=2019-12-27
 |title=Betelgeuse star acting like it's about to explode, even if the odds say it isn't
 |website=[[CNET]]
 |url=https://www.cnet.com/news/betelgeuse-star-acting-like-its-about-to-explode-even-if-odds-say-its-not/
 |access-date=2019-12-30 |df=dmy-all
}}
</ref>
This dropped Betelgeuse from one of the top 10 [[List of brightest stars|brightest stars in the sky]] to outside the top&nbsp;20,<ref name=AT-20191223/> noticeably dimmer than its near neighbor [[Aldebaran]].<ref name=earthsky/> Mainstream media reports discussed speculation that Betelgeuse might be about to explode as a supernova,<ref name=NG-20191226>
{{cite news
 |last=Drake |first=Nadia |author-link=Nadia Drake
 |date=26 December 2019
 |title=A giant star is acting strange, and astronomers are buzzing
 |website=[[National Geographic Society]]
 |url=https://www.nationalgeographic.com/science/2019/12/betelgeuse-is-acting-strange-astronomers-are-buzzing-about-supernova/
 |archive-url=https://web.archive.org/web/20191226131847/https://www.nationalgeographic.com/science/2019/12/betelgeuse-is-acting-strange-astronomers-are-buzzing-about-supernova/
 |url-status=dead
 |archive-date=26 December 2019
 |access-date=26 December 2019
 |quote=The red giant Betelgeuse is the dimmest seen in years, prompting some speculation that the star is about to explode. Here's what we know.
}}
</ref><ref name = Dec2019-WaPo>
{{cite news
 |first = Sarah |last = Kaplan
 |date = 27 December 2019
 |title = Is Betelgeuse, one of the sky's brightest stars, on the brink of a supernova?
 |newspaper = [[The Washington Post]]
 |url = https://www.washingtonpost.com/science/2019/12/27/is-betelgeuse-one-skys-brightest-stars-brink-supernova/
 |access-date = 28 December 2019
}}
</ref><ref name = Dec2019-ABC>
{{cite news
 |first = Kelsie |last = Iorio
 |date = 27 December 2019
 |title = Is Betelgeuse, the red giant star in the constellation Orion, going to explode?
 |website = [[ABC News (Australia)|ABC News]]
 |place = Australia
 |access-date = 28 December 2019
 |url = https://www.abc.net.au/news/2019-12-27/is-betelgeuse-about-to-explode3f/11828624
}}
</ref><ref name = Dec2019-NYP/>
but astronomers note that the supernova is expected to occur within approximately the next 100,000&nbsp;years and is thus unlikely to be imminent.<ref name=NG-20191226/><ref name = Dec2019-ABC/>

By 17&nbsp;February 2020, Betelgeuse's brightness had remained constant for about 10&nbsp;days, and the star showed signs of rebrightening.<ref>
{{cite news
 |first=Bruce |last=Dorminey
 |date=17 February 2020
 |title=Betelgeuse has finally stopped dimming, says astronomer
 |magazine=[[Forbes]]
 |url=https://www.forbes.com/sites/brucedorminey/2020/02/17/betelgeuse-has-finally-stopped-dimming-says-astronomer/#80156477945b
 |access-date=19 February 2020
}}
</ref>
On 22&nbsp;February 2020, Betelgeuse may have stopped dimming altogether, all but ending the dimming episode.<ref name=AT-20200222>
{{cite news
 |last1=Guinan |first1=Edward |last2=Wasatonic |first2=Richard
 |last3=Calderwood |first3=Thomas |last4=Carona |first4=Donald
 |date=22 February 2020
 |title=The fall and rise in brightness of Betelgeuse
 |id=ATel #13512
 |website=[[The Astronomer's Telegram]]
 |url=http://www.astronomerstelegram.org/?read=13512
 |access-date=22 February 2020
}}
</ref>
On 24&nbsp;February 2020, no significant change in the infrared over the last 50 years was detected; this seemed unrelated to the recent visual fading and suggested that an impending core collapse may be unlikely.<ref name=AT-20200224>
{{cite news
 |last1=Gehrz |first1=R.D.
 |display-authors=etal
 |date=24 February 2020
 |title=Betelgeuse remains steadfast in the infrared
 |website=[[The Astronomer's Telegram]]
 |id=ATel #13518 
 |url=http://www.astronomerstelegram.org/?read=13518
 |access-date=24 February 2020
}}
</ref>
Also on 24&nbsp;February 2020, further studies suggested that occluding "large-grain [[circumstellar dust]]" may be the most likely explanation for the dimming of the star.<ref name=EA-20200306>{{cite press release
 |title=Dimming Betelgeuse likely isn't cold, just dusty, new study shows
 |date=6 March 2020
 |publisher=[[University of Washington]]
 |website=[[EurekAlert!]]
 |url=https://www.eurekalert.org/pub_releases/2020-03/uow-dbl030520.php
 |access-date=6 March 2020
 |archive-date=28 February 2021
 |archive-url=https://web.archive.org/web/20210228020242/https://www.eurekalert.org/pub_releases/2020-03/uow-dbl030520.php
 |url-status=dead
 }}</ref><ref name=ARX-20200224>
{{cite journal
 |last1=Levesque |first1=Emily M.
 |last2=Massey |first2=Philip
 |date=24 February 2020
 |title=Betelgeuse just isn't that cool: Effective temperature alone cannot explain the recent dimming of Betelgeuse
 |journal=The Astrophysical Journal Letters
 |volume=891 |issue=2 |page=L37
 |doi=10.3847/2041-8213/ab7935 |doi-access=free
 |bibcode=2020ApJ...891L..37L |bibcode-access=free
 |arxiv=2002.10463 |s2cid=211296241 
}}
</ref>
A study that uses [[observation]]s at [[Submillimetre astronomy|submillimetre]] wavelengths rules out significant contributions from dust absorption. Instead, large [[starspot]]s appear to be the cause for the dimming.<ref>
{{cite journal
 |last1=Dharmawardena |first1=Thavisha E. |last2=Mairs |first2=Steve
 |last3=Scicluna |first3=Peter |last4=Bell |first4=Graham
 |last5=McDonald |first5=Iain |last6=Menten |first6=Karl
 |last7=Weiss |first7=Axel |last8=Zijlstra |first8=Albert
 |date=2020-06-29 |df=dmy-all
 |title=Betelgeuse fainter in the submillimeter too: An analysis of JCMT and APEX monitoring during the recent optical minimum
 |journal=[[The Astrophysical Journal]]
 |volume=897 |issue=1 |page=L9
 |doi=10.3847/2041-8213/ab9ca6 |issn=2041-8213
 |arxiv=2006.09409 |bibcode=2020ApJ...897L...9D
 |s2cid=219721417
|doi-access=free }}
</ref>
Followup studies, reported on 31&nbsp;March 2020 in ''The Astronomer's Telegram'', found a rapid rise in the brightness of Betelgeuse.<ref name=AT-20200331>
{{cite news
 |last=Sigismondi |first=Costantino
 |date=31 March 2020
 |title=Rapid rising of Betelgeuse's luminosity
 |id=ATel #13601 
 |website=[[The Astronomer's Telegram]]
 |url=http://www.astronomerstelegram.org/?read=13601
 |access-date=1 April 2020
}}
</ref>

Betelgeuse is almost unobservable from the ground between May and August because it is too close to the Sun. Before entering its 2020 [[Conjunction (astronomy)|conjunction]] with the Sun, Betelgeuse had reached a brightness of +0.4&nbsp;. Observations with the [[STEREO|STEREO-A]] spacecraft made in June and July&nbsp;2020 showed that the star had dimmed by 0.5 since the last ground-based observation in April. This is surprising, because a maximum was expected for August/September&nbsp;2020, and the next minimum should occur around April&nbsp;2021. However Betelgeuse's brightness is known to vary irregularly, making predictions difficult. The fading could indicate that another dimming event might occur much earlier than expected.<ref>
{{cite news
 |last1=Dupree |first1=Andrea
 |last2=Guinan |first2=Edward 
 |last3=Thompson |first3=William T. 
 |collaboration=STEREO/SECCHI/HI consortium
 |date=28 July 2020
 |title=Photometry of Betelgeuse with the STEREO Mission while in the glare of the Sun from Earth
 |id=ATel #13901 
 |website=[[Astronomer's Telegram]]
 |url=http://astronomerstelegram.org/?read=13901
 |access-date=28 July 2020
}}
</ref>
On 30&nbsp;August 2020, astronomers reported the detection of a second dust cloud emitted from Betelgeuse, and associated with recent substantial dimming (a secondary minimum on 3&nbsp;August) in luminosity of the star.<ref name=AT-20200830>
{{cite news 
 |last1=Sigismondi |first1=Costantino
 |display-authors=etal
 |date=30 August 2020
 |title=Second dust cloud on Betelgeuse
 |website=[[The Astronomer's Telegram]]
 |id=ATel #13982
 |url=http://www.astronomerstelegram.org/?read=13982
 |access-date=31 August 2020
}}
</ref>

In June 2021, the dust was explained as possibly caused by a cool patch on its photosphere<ref>
{{cite journal
 |last1=Montargès |first1=M.
 |last2=Cannon    |first2=E.
 |last3=Lagadec   |first3=E.
 |display-authors=etal
 |date=16 June 2021
 |title=A dusty veil shading Betelgeuse during its Great Dimming
 |journal=Nature
 |volume=594 |issue=7863 |pages=365–368
 |doi=10.1038/s41586-021-03546-8 |pmid=34135524
 |arxiv=2201.10551 |bibcode=2021Natur.594..365M
 |s2cid=235460928
}}
</ref><ref>
{{cite journal
 |last=Levesque |first=E.
 |date=16 June 2021
 |title=Great dimming of Betelgeuse explained
 |journal=[[Nature (journal)|Nature]]
 |volume=594 |issue=7863 |pages=343–344
 |doi=10.1038/d41586-021-01526-6 |pmid=34135515
 |bibcode=2021Natur.594..343L |s2cid=235459976
}}
</ref><ref>
{{cite journal
 |last=Montargès |first=M. 
 |date=16 June 2021
 |journal=[[Nature (journal)|Nature]]
 |title=Imaging the great dimming of Betelgeuse
 |url=https://astronomycommunity.nature.com/posts/imaging-the-great-dimming-of-betelgeuse
}}
</ref><ref name=NYT-20210617>
{{cite news
 |last=Overbye |first=Dennis |authorlink=Dennis Overbye
 |date=17 June 2021
 |title=Betelgeuse merely burped, astronomers conclude
 |newspaper=[[The New York Times]]
 |url=https://www.nytimes.com/2021/06/17/science/betelgeuse-montarges-star-supernova.html
 |access-date=17 June 2021
 |quote=The dramatic dimming of the red supergiant in 2019 was the product of dust, not a prelude to destruction, a new study has found.
}}
</ref>
and in August a second independent group confirmed these results.<ref>
{{cite journal
 |last1=Alexeeva |first1=Sofya |last2=Zhao |first2=Gang
 |last3=Gao |first3=Dong-Yang |last4=Du |first4=Junju
 |last5=Li |first5=Aigen |last6=Li |first6=Kai
 |last7=Hu |first7=Shaoming
 |date=2021-08-05 |df=dmy-all
 |title=Spectroscopic evidence for a large spot on the dimming Betelgeuse
 |journal=Nature Communications
 |volume=12 |issue=1 |page=4719
 |doi=10.1038/s41467-021-25018-3 |doi-access=free
 |pmid=34354072 |pmc=8342547 |arxiv=2108.03472
 |bibcode=2021NatCo..12.4719A |issn=2041-1723 |language=en
}}
</ref><ref>
{{Cite web
 |last=Harris |first=Margaret
 |date=2021-08-06
 |title=New evidence supports dark-spot theory for Betelgeuse's 'great dimming'
 |website=Physics World
 |url=https://physicsworld.com/new-evidence-supports-dark-spot-theory-for-betelgeuses-great-dimming/
 |access-date=2021-08-07 |df=dmy-all
 |language=en-GB
}}
</ref> The dust is thought to have resulted from the cooling of gas ejected from the star. An August 2022<ref>
{{cite journal
 |last1=Dupree    |first1=Andrea K.   |last2=Strassmeier |first2=Klaus G.
 |last3=Calderwood |first3=Thomas     |last4=Granzer     |first4=Thomas
 |last5=Weber     |first5=Michael     |last6=Kravchenko  |first6=Kateryna
 |last7=Matthews  |first7=Lynn D.     |last8=Montarges   |first8=Miguel
 |last9=Tappin    |first9=James       |last10=Thompson   |first10=William T.
 |display-authors=6
 |date=2022-08-02 |df=dmy-all
 |title=The great dimming of Betelgeuse: A surface mass ejection and its consequences
 |journal=[[The Astrophysical Journal]]
 |volume=936 |issue=1 |page=18
 |doi=10.3847/1538-4357/ac7853 |arxiv=2208.01676
 |bibcode=2022ApJ...936...18D |s2cid=251280168
|doi-access=free }}
</ref><ref>
{{cite web
 |last=Garner |first=Rob
 |date=2020-08-13
 |title=Hubble finds Betelgeuse's mysterious dimming due to traumatic outburst
 |website=[[NASA]]
 |url=http://www.nasa.gov/feature/goddard/2020/hubble-finds-that-betelgeuses-mysterious-dimming-is-due-to-a-traumatic-outburst
 |access-date=2022-08-22 |df=dmy-all
}}
</ref><ref>
{{cite web
 |title=How Betelgeuse blew its top and lost its rhythm
 |date=2022-08-22
 |website=[[Physics World]]
 |url=https://physicsworld.com/how-betelgeuse-blew-its-top-and-lost-its-rhythm/
 |access-date=2022-08-22 |df=dmy-all
 |language=en-GB
}}
</ref>
study using the [[Hubble Space Telescope]] confirmed previous research and suggested the dust could have been created by a surface mass ejection. It conjectured as well that the dimming could have come from a short-term minimum coinciding with a long-term minimum producing a grand minimum, a 416-day cycle and 2010&nbsp;day cycle respectively, a mechanism first suggested by astronomer [[Leo Goldberg|L.&nbsp;Goldberg]].<ref>
{{cite journal
 |last=Goldberg |first=L.
 |date=May 1984
 |title=The variability of alpha Orionis
 |journal=Publications of the Astronomical Society of the Pacific
 |language=en
 |volume=96 |pages=366
 |doi=10.1086/131347 |bibcode=1984PASP...96..366G
 |s2cid=121926262 |issn=0004-6280
|doi-access=free
 }}
</ref>
In April&nbsp;2023, astronomers reported the star reached a peak of 0.0 visual and 0.1 V-band magnitude.<ref name=AT-20230422>
{{cite news
 |last1=Sigismondi |first1=Constantino
 |display-authors=etal
 |date=22 April 2023
 |title=Monitoring Betelgeuse at its brightest
 |id=Atel #16001
 |website=[[The Astronomer's Telegram]]
 |url=https://www.astronomerstelegram.org/?read=16001
 |access-date=22 April 2023
}}
</ref>

== Observation ==
[[File:Orion Head to Toe.jpg|thumb|right|Image showing Betelgeuse (top left) and the dense nebulae of the [[Orion molecular cloud complex]] ([[Rogelio Bernal Andreo]])]]
As a result of its distinctive orange-red color and position within Orion, Betelgeuse is easy to find with the naked eye. It is one of three stars that make up the [[Winter Triangle]] [[asterism (astronomy)|asterism]], and it marks the center of the [[Winter Hexagon]]. It can be seen rising in the east at the beginning of January of each year, just after sunset. Between mid-September and mid-March (best in mid-December), it is visible to virtually every inhabited region of the globe, except in [[Antarctica]] at latitudes south of 82°. In May (moderate northern latitudes) or June (southern latitudes), the red supergiant can be seen briefly on the western horizon after sunset, reappearing again a few months later on the eastern horizon before sunrise. In the intermediate period (June–July, centered around mid June), it is invisible to the naked eye (visible only with a telescope in daylight), except around midday low in the north in Antarctic regions between 70° and 80° south latitude (during midday twilight in [[polar night]], when the Sun is below the horizon).

Betelgeuse is a variable star whose [[apparent magnitude|visual magnitude]] ranges between 0.0 and +1.6&nbsp;.<ref name=vsx/> There are periods during which it surpasses Rigel to become the sixth brightest star, and occasionally it will become even brighter than [[Capella]]. At its faintest, Betelgeuse can fall behind [[Deneb]] and [[Beta Crucis]], themselves both slightly variable, to be the twentieth-brightest star.<ref name=BURNHAM/>

Betelgeuse has a B–V [[color index]] of 1.85 – a figure which points to its pronounced "redness". The photosphere has an extended [[Stellar atmosphere|atmosphere]], which displays strong lines of [[Spectral line|emission]] rather than [[Spectral line|absorption]], a phenomenon that occurs when a star is surrounded by a thick gaseous envelope (rather than ionized). This extended gaseous atmosphere has been observed moving toward and away from Betelgeuse, depending on fluctuations in the photosphere. Betelgeuse is the brightest near-infrared source in the sky with a [[J band (infrared)|J&nbsp;band]] [[Magnitude (astronomy)|magnitude]] of −2.99;<ref name="2MASS-brightest">{{cite press release |date=7 September 2009 |title=Very bright stars in the 2MASS Point Source Catalog (PSC) |publisher=The Two Micron All Sky Survey at IPAC |last1=Cutri |first1=R. |last2=Skrutskie |first2=M. |url=http://www.ipac.caltech.edu/2mass/releases/allsky/doc/sec1_6b.html#satr1|access-date=28 December 2011}}</ref> only about 13% of the star's [[radiant energy]] is emitted as visible light. If human eyes were sensitive to radiation at all wavelengths, Betelgeuse would appear as the brightest star in the night sky.<ref name="BURNHAM" />
[[File:Betelgeuse_(star).jpg|thumb|219x219px|Betelgeuse seen close-up]]
Catalogues list up to nine faint visual companions to Betelgeuse. They are at distances of about one to four arc-minutes and all are fainter than 10th&nbsp;magnitude.<ref name="CCDM">{{cite web |title=CCDM (Catalog of Components of Double & Multiple stars (Dommanget+ 2002) |work=[[VizieR]] |publisher=[[Centre de Données astronomiques de Strasbourg]] |url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?CCDM%20J05552%2b0724AP |access-date=22 August 2010}}</ref><ref name="wds">{{cite journal |bibcode=2001AJ....122.3466M |title=The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog |journal=The Astronomical Journal |volume=122 |issue=6 |pages=3466 |last1=Mason |first1=Brian D. |last2=Wycoff |first2=Gary L. |last3=Hartkopf |first3=William I. |last4=Douglass |first4=Geoffrey G. |last5=Worley |first5=Charles E. |year=2001 |doi=10.1086/323920 |doi-access=free}}</ref>

=== Distance measurements ===
[[File:USA.NM.VeryLargeArray.02.jpg|thumb|right|[[National Radio Astronomy Observatory|NRAO]]'s [[Very Large Array]] used to derive Betelgeuse's 2008 distance estimate]]

[[Parallax]] is the apparent change of the position of an object, measured in seconds of arc, caused by the change of position of the observer of that object. [[Parallax in astronomy|Parallax is used in astronomy]] to estimate distances to the nearest stars. As the Earth orbits the Sun, every star is seen to shift by a fraction of an arc second, which measure, combined with the baseline provided by the Earth's orbit gives the distance to that star. Since the first successful [[parallax]] measurement by [[Friedrich Bessel]] in 1838, astronomers have been puzzled by Betelgeuse's apparent distance. Knowledge of the star's distance improves the accuracy of other stellar parameters, such as [[Stellar luminosity|luminosity]] that, when combined with an angular diameter, can be used to calculate the physical radius and [[effective temperature]]; luminosity and [[Natural abundance|isotopic abundances]] can also be used to estimate the [[Stellar evolution|stellar age]] and [[Intermediate mass star|mass]].<ref name="HARPER">
{{cite journal
 | last1=Harper |first1=Graham M.
 | last2=Brown  |first2=Alexander
 | last3=Guinan |first3=Edward F.
 | title=A new VLA-Hipparcos distance to Betelgeuse and its implications
 | journal=The Astronomical Journal
 | date=April 2008
 | volume=135 | issue=4 | pages=1430–40
 | bibcode=2008AJ....135.1430H
 | doi=10.1088/0004-6256/135/4/1430 | doi-access=free
 }}</ref>

When the first interferometric studies were performed on the star's diameter in 1920, the assumed parallax was {{val|0.0180|ul="}}. This equated to a distance of {{val|56|ul=pc}} or roughly {{val|180|ul=ly}}, producing not only an inaccurate radius for the star but every other stellar characteristic. Since then, there has been ongoing work to measure the distance of Betelgeuse, with proposed distances as high as {{val|400|u=pc}} or about {{val|1300|u=ly|fmt=commas}}.<ref name="HARPER" />

Before the publication of the [[Hipparcos Catalogue]] (1997), there were two slightly conflicting parallax measurements for Betelgeuse. The first, in 1991, gave a parallax of {{val|9.8|4.7|ul=mas}}, yielding a distance of roughly {{val|102|u=pc}} or {{val|330|u=ly}}.<ref name=YALEPLX>
{{cite journal
 | last1=van&nbsp;Altena |first1=W.F.
 | last2=Lee  |first2=J.T.
 | last3=Hoffleit |first3=D.
 | title=Yale Trigonometric Parallaxes Preliminary
 | journal=Yale University Observatory (1991)
 | date=October 1995
 | bibcode=1995yCat.1174....0V
 | volume=1174
 | page=0
}}
</ref> The second was the [[Hipparcos#Hipparcos Input Catalogue|Hipparcos Input Catalogue]] (1993) with a trigonometric parallax of {{val|5|4|u=mas}}, a distance of {{val|200|u=pc}} or {{val|650|u=ly}}.<ref name="HIC">
{{cite web
 | title=Hipparcos Input Catalogue, Version&nbsp;2 (Turon+ 1993)
 | work=[[VizieR]]
 | year=1993
 | publisher=[[Centre de Données astronomiques de Strasbourg]]
 | url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIC%2027989
 | access-date=20 June 2010
}}
</ref> Given this uncertainty, researchers were adopting a wide range of distance estimates, leading to significant variances in the calculation of the star's attributes.<ref name="HARPER" />

The results from the Hipparcos mission were released in 1997. The measured parallax of Betelgeuse was {{val|7.63|1.64|u=mas}}, which equated to a distance of roughly {{val|131|u=pc}} or {{val|427|u=ly}}, and had a smaller reported error than previous measurements.<ref name="PERRYMAN">
{{cite journal
 | display-authors=6
 | last1=Perryman | first1=M.A.C. | last2=Lindegren | first2=L.
 | last3=Kovalevsky | first3=J. | last4=Hoeg | first4=E.
 | last5=Bastian | first5=U. | last6=Bernacca | first6=P.L.
 | last7=Crézé | first7=M. | last8=Donati | first8=F.
 | last9=Grenon | first9=M.
 | title=The Hipparcos Catalogue
 | journal=[[Astronomy & Astrophysics]]
 | year=1997 | volume=323 | pages=L49–L52
 | bibcode=1997A&A...323L..49P
}}
</ref>
However, later evaluation of the Hipparcos parallax measurements for variable stars like Betelgeuse found that the uncertainty of these measurements had been underestimated.<ref name=EYER>
{{cite conference
 | last1=Eyer |first1=L.
 | last2=Grenon |first2=M.
 | year=2000
 | title=Problems encountered in the Hipparcos variable stars analysis
 | conference=6th Vienna Workshop in Astrophysics
 | book-title=Delta Scuti and Related Stars – Reference Handbook and Proceedings of the 6th Vienna Workshop in Astrophysics
 | series=ASP Conference Series
 | publisher=[[Astronomical Society of the Pacific]]
 | volume=210 | page=482
 | place=Vienna, Austria
 | bibcode=2000ASPC..210..482E
 | isbn=978-1-58381-041-5 | arxiv = astro-ph/0002235
}}
</ref>
In 2007, an improved figure of {{val|6.55|0.83}} was calculated, hence a much tighter [[Margin of error|error factor]] yielding a distance of roughly {{val|152|20|u=pc}} or {{val|500|65|u=ly}}.<ref name=hipparcos>{{cite journal | title=Hipparcos, the new reduction | last1=van&nbsp;Leeuwen | first1=F. |display-authors=etal |date=November 2007 | id=[[VizieR]] | issue=2 | pages=653–664 | volume=474 | doi=10.1051/0004-6361:20078357 | journal=[[Astronomy and Astrophysics]] | bibcode=2007A&A...474..653V |arxiv = 0708.1752| s2cid=18759600 }}</ref>

In 2008, measurements using the [[Very Large Array]] (VLA) produced a [[Radio astronomy|radio]] solution of {{val|5.07|1.10|u=mas}}, equaling a distance of {{val|197|45|u=pc}} or {{val|643|146|u=ly}}.<ref name="HARPER" /> As the researcher, Harper, points out: "The revised Hipparcos parallax leads to a larger distance ({{val|152|20|u=pc}}) than the original; however, the [[astrometric]] solution still requires a significant [[cosmic noise]] of 2.4 mas. Given these results it is clear that the Hipparcos data still contain systematic errors of unknown origin." Although the radio data also have systematic errors, the Harper solution combines the datasets in the hope of mitigating such errors.<ref name="HARPER" /> An updated result from further observations with [[Atacama Large Millimeter Array|ALMA]] and [[e-Merlin]] gives a parallax of {{val|4.51|0.8}} mas and a distance of {{val|222|34|48}} pc or {{val|724|111|156}} ly.<ref name=harper2017>{{cite journal|bibcode=2017AJ....154...11H|arxiv=1706.06020|title=An Updated 2017 Astrometric Solution for Betelgeuse|journal=The Astronomical Journal|volume=154|issue=1|pages=11|last1=Harper|first1=G. M.|last2=Brown|first2=A.|last3=Guinan|first3=E. F.|last4=O'Gorman|first4=E.|last5=Richards|first5=A. M. S.|last6=Kervella|first6=P.|last7=Decin|first7=L.|year=2017|doi=10.3847/1538-3881/aa6ff9|s2cid=59125676 |doi-access=free }}</ref>

In 2020, new observational data from the space-based ''Solar Mass Ejection Imager'' aboard the [[Coriolis (satellite)|Coriolis satellite]] and three different modeling techniques produced a refined parallax of {{val|5.95|0.58|0.8|u=mas}}, a radius of {{val|764|116|62|u=Solar radius}}, and a distance of {{val|168.1|27.5|14.4|u=pc}} or {{val|548|90|49|u=ly}}, which would imply Betelgeuse is nearly 25% smaller and 25% closer to Earth than previously thought.<ref name=joyce2020>{{cite journal |doi=10.3847/1538-4357/abb8db |title=Standing on the Shoulders of Giants: New Mass and Distance Estimates for Betelgeuse through Combined Evolutionary, Asteroseismic, and Hydrodynamic Simulations with MESA |year=2020 |last1=Joyce |first1=Meridith |last2=Leung |first2=Shing-Chi |last3=Molnár |first3=László |last4=Ireland |first4=Michael |last5=Kobayashi |first5=Chiaki |last6=Nomoto |first6=Ken'Ichi |journal=The Astrophysical Journal |volume=902 |issue=1 |page=63 |arxiv=2006.09837 |bibcode=2020ApJ...902...63J |s2cid=221507952 |doi-access=free }}</ref>

Another study in 2022 suggests Betelgeuse to be smaller and closer than previously thought based on historical records which revealed Betelgeuse changed in color from yellow to red in the last thousand years. This color change suggests a mass of {{solar mass|14}}, considerably less than previous estimates, and the best-fit [[stellar evolution|evolutionary track]] gives an estimate as low as 125 parsecs (410 light-years), consistent with the ''Hipparcos'' data.<ref name="Neuhauser2022" />

The [[European Space Agency]]'s current [[Gaia mission]] is unable to produce good parallax results for stars like Betelgeuse which are brighter than the approximately V=6 saturation limit of the mission's instruments.<ref name="ESA1">{{cite web|title=Science Performance|publisher=[[European Space Agency]]|url=http://www.rssd.esa.int/index.php?page=Science_Performance&project=GAIA|date=19 February 2013|access-date=1 March 2013}}</ref><ref name=prusti>{{cite journal |first1 = T. |last1 = Prusti |collaboration = GAIA Collaboration | date = 2016 | title = The ''Gaia'' mission | type = forthcoming article | journal = [[Astronomy and Astrophysics]] | doi = 10.1051/0004-6361/201629272 | url = http://www.aanda.org/articles/aa/pdf/forth/aa29272-16.pdf | access-date = 21 September 2016 | bibcode=2016A&A...595A...1G | volume=595 | pages=A1 |arxiv = 1609.04153 | hdl = 2445/127856 | s2cid = 9271090 }}</ref> Because of this limitation, there was no data on Betelgeuse in [[Gaia Data Release 2]], from 2018<ref>{{cite web |url=https://gea.esac.esa.int/archive/ |title=Welcome to the Gaia Archive |website=[[European Space Agency]] |access-date=2020-09-03 }}</ref> or Data Release 3 from 2022.<ref>{{cite web | url=https://earthsky.org/astronomy-essentials/how-far-is-betelgeuse | title=EarthSky &#124; How far is Betelgeuse, the famous doomed star? | date=8 January 2023 }}</ref>

=== Variability ===
[[File:Light curve of Betelgeuse.png|thumb|upright=1.15|[[AAVSO]] [[Photometric system|V-band]] [[light curve]] of Betelgeuse (Alpha Orionis) from Dec 1988 to Aug 2002]]
[[File:Betelgeuse.jpg|thumb|[[Orion (constellation)|Orion]], with Betelgeuse at its usual [[apparent magnitude|magnitude]] (left) and during the unusually deep minimum in early 2020 (right)]]

Betelgeuse is classified as a [[semiregular variable star]], indicating that some periodicity is noticeable in the brightness changes, but amplitudes may vary, cycles may have different lengths, and there may be standstills or periods of irregularity. It is placed in subgroup SRc; these are pulsating red supergiants with amplitudes around one magnitude and periods from tens to hundreds of days.<ref name=gcvs/>

Betelgeuse typically shows only small brightness changes near to magnitude +0.5, although at its extremes it can become as bright as magnitude 0.0 or as faint as magnitude +1.6. Betelgeuse is listed in the [[General Catalogue of Variable Stars]] with a possible period of 2,335 days.<ref name=gcvs/> More detailed analyses have shown a main period near 400 days, a short period of 185 days,<ref name=joyce2020/> and a longer secondary period around 2,100 days.<ref name=montarges2016>{{cite journal|bibcode=2016A&A...588A.130M|arxiv=1602.05108|title=The close circumstellar environment of Betelgeuse. IV. VLTI/PIONIER interferometric monitoring of the photosphere|journal=Astronomy & Astrophysics|volume=588|pages=A130|last1=Montargès|first1=M.|last2=Kervella|first2=P.|last3=Perrin|first3=G.|last4=Chiavassa|first4=A.|last5=Le Bouquin|first5=J.-B.|last6=Aurière|first6=M.|last7=López Ariste|first7=A.|last8=Mathias|first8=P.|last9=Ridgway|first9=S. T.|last10=Lacour|first10=S.|last11=Haubois|first11=X.|last12=Berger|first12=J.-P.|year=2016|doi=10.1051/0004-6361/201527028|s2cid=53404211}}</ref><ref name=kiss>{{cite journal|bibcode=2006MNRAS.372.1721K|arxiv=astro-ph/0608438|title=Variability in red supergiant stars: Pulsations, long secondary periods and convection noise|journal=Monthly Notices of the Royal Astronomical Society|volume=372|issue=4|pages=1721–1734|last1=Kiss|first1=L. L.|last2=Szabó|first2=Gy. M.|last3=Bedding|first3=T. R.|year=2006|doi=10.1111/j.1365-2966.2006.10973.x|doi-access=free |s2cid=5203133}}</ref> The lowest reliably-recorded [[UBV photometric system|V-band]] magnitude of +1.614 was reported in February 2020.

Radial pulsations of red supergiants are well-modelled and show that periods of a few hundred days are typically due to [[fundamental mode|fundamental]] and first [[overtone]] pulsation.<ref name=guo>{{cite journal|bibcode=2002ApJ...565..559G|title=Evolution and Pulsation of Red Supergiants at Different Metallicities|journal=The Astrophysical Journal|volume=565|issue=1|pages=559–570|last1=Guo|first1=J. H.|last2=Li|first2=Y.|year=2002|doi=10.1086/324295|doi-access=free}}</ref> [[Absorption line|Lines]] in the [[stellar spectrum|spectrum]] of Betelgeuse show [[doppler shift]]s indicating [[radial velocity]] changes corresponding, very roughly, to the brightness changes. This demonstrates the nature of the pulsations in size, although corresponding temperature and spectral variations are not clearly seen.<ref name=goldberg>{{cite journal|bibcode=1984PASP...96..366G|title=The variability of alpha Orionis|journal=Astronomical Society of the Pacific|volume=96|pages=366|last1=Goldberg|first1=L.|year=1984|doi=10.1086/131347|doi-access=free}}</ref> Variations in the diameter of Betelgeuse have also been measured directly.<ref name=RAVI1/> [[Overtone|First overtone]] pulsations of 185 days have been observed, and the ratio of the fundamental to overtone periods gives valuable information about the internal structure of the star and its age.<ref name=joyce2020/>

The source of the long secondary periods is unknown, but they cannot be explained by [[radial pulsations]].<ref name=kiss/> Interferometric observations of Betelgeuse have shown hotspots that are thought to be created by massive convection cells, a significant fraction of the diameter of the star and each emitting 5–10% of the total light of the star.<ref name=HAUBOIS/><ref name=montarges2016/> One theory to explain long secondary periods is that they are caused by the evolution of such cells combined with the rotation of the star.<ref name=kiss/> Other theories include close binary interactions, [[Chromosphere|chromospheric]] magnetic activity influencing mass loss, or non-radial pulsations such as [[G-mode pulsation|g-mode]]s.<ref name=wood>{{cite journal|bibcode=2004ApJ...604..800W|title=Long Secondary Periods in Pulsating Asymptotic Giant Branch Stars: An Investigation of their Origin|journal=The Astrophysical Journal|volume=604|issue=2|pages=800|last1=Wood|first1=P. R.|last2=Olivier|first2=E. A.|last3=Kawaler|first3=S. D.|year=2004|doi=10.1086/382123|doi-access=free}}</ref>

In addition to the discrete dominant periods, small-amplitude [[stochastic]] variations are seen. It is proposed that this is due to [[Granule (solar physics)|granulation]], similar to the same effect on the sun but on a much larger scale.<ref name=kiss/>

=== Diameter ===
{{See also|List of largest stars}}
[[File:Arcturus to Betelgeuse comparison.jpg|thumb|Size comparison between [[Arcturus]], [[Rigel]], [[S Doradus]], [[Antares]], and Betelgeuse]]
[[File:Mukyv354.png|thumb|upright=1.15|Size comparison of Betelgeuse, [[Mu Cephei]], [[KY Cygni]], and [[V354 Cephei]], according to [[Emily Levesque]]<ref>{{Cite journal |last1=Levesque |first1=Emily M. |last2=Massey |first2=Philip |last3=Olsen |first3=K. A. G. |last4=Plez |first4=Bertrand |last5=Josselin |first5=Eric |last6=Maeder |first6=Andre |last7=Meynet |first7=Georges |date=August 2005  |title=The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought |journal=The Astrophysical Journal |volume=628 |issue=2 |pages=973–985 |doi=10.1086/430901 |issn=0004-637X|arxiv=astro-ph/0504337 |bibcode=2005ApJ...628..973L }}</ref>]]

On 13 December 1920, Betelgeuse became the first star outside the Solar System to have the angular size of its photosphere measured.<ref name="MICHELSON" /> Although interferometry was still in its infancy, the experiment proved a success. The researchers, using a uniform disk model, determined that Betelgeuse had a diameter of {{val|0.047|u="}}, although the stellar disk was likely 17% larger due to the [[limb darkening]], resulting in an estimate for its angular diameter of about 0.055".<ref name=MICHELSON/><ref name=TOWNES1>{{cite journal
 | title= A Systematic Change with Time in the Size of Betelgeuse
 | last1=Townes |first1=C.H.   | last2=Wishnow |first2=E.H.
 | last3=Hale   |first3=D.D.S. | last4=Walp    |first4=B.
 | journal=The Astrophysical Journal Letters
 | volume= 697
 | issue= 2
 | pages= L127–28
 | year=2009
 | bibcode=2009ApJ...697L.127T
 | doi=10.1088/0004-637X/697/2/L127| doi-access=free
 }}</ref> Since then, other studies have produced angular diameters that range from 0.042 to {{val|0.069|u="}}.<ref name=BONNEAU1973/><ref name=WEINER/><ref name=BALEGA>
{{cite journal
 | last1=Balega   |first1=Iu.       | last2=Blazit   |first2=A.
 | last3=Bonneau  |first3=D.        | last4=Koechlin |first4=L.
 | last5=Labeyrie |first5=A.        | last6=Foy      |first6=R.
 | title=The angular diameter of Betelgeuse
 | journal=Astronomy and Astrophysics
 |date=November 1982
 | volume=115
 | issue= 2
 | pages=253–56
 | bibcode=1982A&A...115..253B
}}
</ref>
Combining these data with historical distance estimates of 180 to {{val|815|u=ly}} yields a projected radius of the stellar disk of anywhere from 1.2 to {{val|8.9|u=AU}}. Using the Solar System for comparison, the orbit of [[Solar System#Mars|Mars]] is about {{val|1.5|u=AU}}, [[Solar System#Ceres|Ceres]] in the [[asteroid belt]] {{val|2.7|u=AU}}, [[Solar System#Jupiter|Jupiter]] {{val|5.5|u=AU}}—so, assuming Betelgeuse occupying the place of the Sun, its photosphere might extend beyond the Jovian orbit, not quite reaching [[Solar System#Saturn|Saturn]] at {{val|9.5|u=AU}}.
[[File:Betelgeuse radio wavelengths.jpg|thumb|right|upright=1.35 |Radio image from 1998 showing the size of Betelgeuse's photosphere (circle) and the effect of convective forces on the star's atmosphere]]

The precise diameter has been hard to define for several reasons:

# Betelgeuse is a pulsating star, so its diameter changes with time;
# The star has no definable "edge" as limb darkening causes the optical emissions to vary in color and decrease the farther one extends out from the center;
# Betelgeuse is surrounded by a circumstellar envelope composed of matter ejected from the star—matter which absorbs and emits light—making it difficult to define the photosphere of the star;<ref name=UCBERKELEY2009/>
# Measurements can be taken at varying [[wavelengths]] within the [[electromagnetic spectrum]] and the difference in reported diameters can be as much as 30–35%, yet comparing one finding with another is difficult as the star's apparent size differs depending on the wavelength used.<ref name=UCBERKELEY2009/> Studies have shown that the measured angular diameter is considerably larger at ultraviolet wavelengths, decreases through the visible to a minimum in the near-infrared, and increase again in the mid-infrared spectrum;<ref name=GILLILAND1/><ref name=PERRIN2>
{{cite journal
 |last1=Perrin |first1=G. |last2=Ridgway |first2=S.T.
 |last3=Coudé du Foresto |first3=V. |last4=Mennesson |first4=B.
 |last5=Traub |first5=W.A. |last6=Lacasse |first6=M.G.
 |year=2004
 |title=Interferometric observations of the supergiant stars {{nobr|{{mvar|α}} Orionis}} and {{nobr|{{mvar|α}} Herculis}} with FLUOR at IOTA
 |journal=[[Astronomy and Astrophysics]]
 |volume=418 |issue=2 |pages=675–685
 |doi=10.1051/0004-6361:20040052
 |arxiv=astro-ph/0402099  |s2cid=119065851
 |bibcode=2004A&A...418..675P
 |quote=Assuming a distance of {{val|197|45|u=pc}}, an angular distance of {{val|43.33|0.04|u=mas}} would equate to a radius of {{val|4.3|u=AU}} or {{solar radius|920}}
}}
</ref><ref name=YOUNG>
{{cite press release
 | last=Young  | first=John
 | date=24 November 2006
 | title=Surface imaging of Betelgeuse with COAST and the WHT
 | publisher=[[University of Cambridge]]
 | quote=Images of hotspots on the surface of Betelgeuse taken at visible and infra-red wavelengths using high resolution ground-based [[astronomical interferometer|interferometers]]
 | url=http://www.mrao.cam.ac.uk/telescopes/coast/betel.html
 | access-date=21 June 2007
 | url-status=dead
 | archive-url=https://web.archive.org/web/20070614111315/http://www.mrao.cam.ac.uk/telescopes/coast/betel.html
 | archive-date=14 June 2007
 | df=dmy-all
}}
</ref>
# [[Scintillation (astronomy)|Atmospheric twinkling]] limits the resolution obtainable from ground-based telescopes since turbulence degrades angular resolution.<ref name=BUSCHER/>

The generally reported radii of large cool stars are [[Rosseland optical depth|Rosseland radii]], defined as the radius of the photosphere at a specific optical depth of two-thirds. This corresponds to the radius calculated from the effective temperature and bolometric luminosity. The Rosseland radius differs from directly measured radii, with corrections for [[limb darkening]] and the observation wavelength.<ref name=dyck>{{cite journal |doi=10.1086/300453 |title=Radii and effective temperatures for K and M&nbsp;giants and supergiants. II |journal=The Astronomical Journal |volume=116 |issue=2 |page=981 |year=1998 |last1=Dyck |first1=H.M. |last2=van&nbsp;Belle |first2=G.T. |last3=Thompson |first3=R.R. |bibcode=1998AJ....116..981D |citeseerx=10.1.1.24.1889 |s2cid=16674990 }}</ref> For example, a measured angular diameter of 55.6&nbsp;[[milliarcsecond|mas]] would correspond to a Rosseland mean diameter of 56.2&nbsp;mas, while further corrections for the existence of surrounding dust and gas shells would give a diameter of {{val|41.9|u=mas}}.<ref name=dolan2016/>

To overcome these challenges, researchers have employed various solutions. Astronomical interferometry, first conceived by [[Hippolyte Fizeau]] in 1868, was the seminal concept that has enabled major improvements in modern telescopy and led to the creation of the [[Michelson interferometer]] in the 1880s, and the first successful measurement of Betelgeuse.<ref name=PERRIN1>
{{cite journal
 | last1=Perrin | first1=Guy | last2=Malbet | first2=Fabien
 | title=Observing with the VLTI
 | journal=EAS Publications Series
 | year=2003
 | volume= 6
 | bibcode=2003EAS.....6D...3P
 | page=3
 | doi=10.1051/eas/20030601| doi-access=free
 }}
</ref>
Just as human [[depth perception]] increases when two eyes instead of one perceive an object, Fizeau proposed the observation of stars through two [[apertures]] instead of one to obtain [[Interference (wave propagation)|interferences]] that would furnish information on the star's spatial intensity distribution. The science evolved quickly and multiple-aperture interferometers are now used to capture [[Speckle imaging|speckled images]], which are synthesized using [[Fourier analysis]] to produce a portrait of high resolution.<ref name=APOD1>
{{cite APOD
 | title=3 ATs
 | date=21 April 2012
 | access-date=17 August 2012
 | quote=Photograph showing three of the four enclosures which house 1.8&nbsp;meter Auxiliary Telescopes (ATs) at the [[Paranal Observatory]] in the [[Atacama Desert]] region of [[Chile]].}}</ref> It was this methodology that identified the hotspots on Betelgeuse in the 1990s.<ref name=WORDEN>
{{cite magazine
 | last=Worden | first=S.
 | title=Speckle Interferometry
 | magazine=[[New Scientist]]
 | year=1978
 | volume=78
 | pages=238–40
 | bibcode=1978NewSc..78..238W
}}
</ref>
Other technological breakthroughs include [[adaptive optics]],<ref name=RODDIER1>
{{cite conference
 | last=Roddier | first=F.
 | year=1999
 | title=Ground-based interferometry with adaptive optics
 | book-title=Working on the Fringe: Optical and IR interferometry from ground and space 
 | series=ASP Conference
 | volume=194 | page=318
 | publisher = [[Astronomical Society of the Pacific]]
 | isbn=978-1-58381-020-0
 | bibcode=1999ASPC..194..318R
}}
</ref> [[Space observatory|space observatories]] like Hipparcos, [[Hubble Space Telescope|Hubble]] and [[Spitzer Space Telescope|Spitzer]],<ref name=GILLILAND1/><ref name=NASA1>
{{cite press release
 | title=Top five breakthroughs from Hubble's workhorse camera
 | date=4 May 2009
 | series=[[NASA Jet Propulsion Laboratory]]
 | publisher = [[California Institute of Technology]]
 | place = Pasadena, CA
 | url=http://www.jpl.nasa.gov/news/features.cfm?feature=2132
 | access-date=28 August 2007 | url-status=dead
 | archive-url=https://web.archive.org/web/20090507102643/http://www.jpl.nasa.gov/news/features.cfm?feature=2132
 | archive-date=7 May 2009
}}
</ref>
and the [[AMBER (Very Large Telescope)|Astronomical Multi-BEam Recombiner (AMBER)]], which combines the beams of three telescopes simultaneously, allowing researchers to achieve milliarcsecond [[spatial resolution]].<ref name=MELNICK>
{{cite press release
 | last1=Melnick | first1=J. | last2=Petrov | first2=R.
 | last3=Malbet | first3=F.
 | date=23 February 2007
 | url=http://www.eso.org/public/news/eso0706/
 | title=The Sky Through Three Giant Eyes, AMBER Instrument on VLT Delivers a Wealth of Results
 | publisher=[[European Southern Observatory]]
 |access-date=29 August 2007
}}
</ref><ref name=WITTKOWSKI>
{{cite journal
 |last = Wittkowski |first = M.
 |date = 23 February 2007
 |journal = [[New Astronomy Reviews]]
 |title = MIDI and AMBER from the user's point of view
 |volume = 51  |issue = 8–9  |pages = 639–649
 |bibcode = 2007NewAR..51..639W
 |doi= 10.1016/j.newar.2007.04.005
 |url = http://www.vlti.org/events/assets/1/proceedings/2.4_Wittkowski.pdf
 |access-date = 29 August 2007 |url-status = dead
 |archive-url = https://web.archive.org/web/20110728164017/http://www.vlti.org/events/assets/1/proceedings/2.4_Wittkowski.pdf
 |archive-date = 28 July 2011
 |df = dmy-all
}}
</ref>

Observations in different regions of the electromagnetic spectrum—the visible, near-infrared ([[Infrared#Astronomy division scheme|NIR]]), mid-infrared (MIR), or radio—produce very different angular measurements. In 1996, Betelgeuse was shown to have a uniform disk of {{val|56.6|1.0|u=mas}}. In 2000, a [[Space Sciences Laboratory]] team measured a diameter of {{val|54.7|0.3|u=mas}}, ignoring any possible contribution from hotspots, which are less noticeable in the mid-infrared.<ref name="WEINER" /> Also included was a theoretical allowance for limb darkening, yielding a diameter of {{val|55.2|0.5|u=mas}}. The earlier estimate equates to a radius of roughly {{val|5.6|u=AU}} or {{solar radius|1,200}}, assuming the 2008 Harper distance of {{val|197.0|45|u=pc}},<ref name=SMITH2009>
{{cite journal
 |last1=Smith  |first1 = Nathan
 |last2=Hinkle |first2 = Kenneth H.
 |last3=Ryde   |first3 = Nils
 |date=March 2009
 |title=Red supergiants as potential type&nbsp;IIn supernova progenitors: Spatially resolved 4.6&nbsp;μm CO emission around VY&nbsp;CMa and Betelgeuse
 |journal=The Astronomical Journal
 |volume=137 |issue=3 |pages=3558–3573
 |arxiv=0811.3037 |doi=10.1088/0004-6256/137/3/3558
 |bibcode=2009AJ....137.3558S |s2cid=19019913
}}
</ref>
a figure roughly the size of the Jovian orbit of {{val|5.5|u=AU}}.<ref name=ASTRONOMYMAG2009>
{{cite news
 | title=Red giant star Betelgeuse in the constellation Orion is mysteriously shrinking
 | date=June 2009
 | magazine=[[Astronomy Magazine]]
 | url=http://www.astronomy.com/en/News-Observing/News/2009/06/Red%20giant%20star%20Betelgeuse%20in%20the%20constellation%20Orion%20is%20mysteriously%20shrinking.aspx
 | access-date=14 September 2012
}}
</ref><ref name=APOD2>
{{cite APOD
 |title=The spotty surface of Betelgeuse
 |date=6 January 2010
 |access-date=18 July 2010
}}
</ref>

In 2004, a team of astronomers working in the near-infrared announced that the more accurate photospheric measurement was {{val|43.33|0.04|u=mas}}. The study also put forth an explanation as to why varying wavelengths from the visible to mid-infrared produce different diameters: The star is seen through a thick, warm extended atmosphere. At short wavelengths (the visible spectrum) the atmosphere scatters light, thus slightly increasing the star's diameter. At near-infrared wavelengths ([[K band (infrared)|K]] and [[L band (infrared)|L bands]]), the scattering is negligible, so the classical photosphere can be directly seen; in the mid-infrared the scattering increases once more, causing the thermal emission of the warm atmosphere to increase the apparent diameter.<ref name=PERRIN2/>
[[File:Orion's Big Head Revealed in Infrared.jpg|thumb|right|Infrared image of Betelgeuse, [[Meissa]] and [[Bellatrix]] with surrounding [[nebula]]e]]

Studies with the [[Infrared Optical Telescope Array|IOTA]] and VLTI published in 2009 brought strong support to the idea of dust shells and a molecular shell (MOLsphere) around Betelgeuse, and yielded diameters ranging from 42.57 to {{val|44.28|u=mas}} with comparatively insignificant margins of error.<ref name=HAUBOIS>
{{cite journal
 | last1=Haubois  | first1=X.        | last2=Perrin    | first2=G.
 | last3=Lacour   | first3=S.        | last4=Verhoelst | first4=T.
 | last5=Meimon   | first5=S.        | last6=Mugnier   | first6=L.
 | last7=Thiébaut | first7=E.        | last8=Berger    | first8=J.P.
 | last9=Ridgway  | first9=S.T.
 | display-authors=6
 | year=2009
 | title=Imaging the spotty surface of Betelgeuse in the H&nbsp;band
 | journal=[[Astronomy & Astrophysics]]
 | volume=508 | issue=2  | pages=923–32
 | arxiv = 0910.4167 | s2cid=118593802
 | bibcode=2009A&A...508..923H
 | doi=10.1051/0004-6361/200912927
}}
</ref><ref name=HERNANDEZ>
{{cite journal
 | last1=Hernandez Utrera |first1=O.
 | last2=Chelli |first2=A
 | title=Accurate Diameter Measurement of Betelgeuse Using the VLTI/AMBER Instrument
 | journal=Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias
 | year=2009
 | volume=37
 | pages=179–80
 | url=http://www.astroscu.unam.mx/rmaa/RMxAC..37/PDF/RMxAC..37_ohernandez.pdf
 | bibcode=2009RMxAC..37..179H
 | access-date=16 August 2010
 | archive-date=15 July 2011
 | archive-url=https://web.archive.org/web/20110715041557/http://www.astroscu.unam.mx/rmaa/RMxAC..37/PDF/RMxAC..37_ohernandez.pdf
 | url-status=dead
 }}</ref> In 2011, a third estimate in the near-infrared corroborating the 2009 numbers, this time showing a limb-darkened disk diameter of {{val|42.49|0.06|u=mas}}.<ref name=OHNAKA2011>{{cite journal|doi=10.1051/0004-6361/201016279|title=Imaging the dynamical atmosphere of the red supergiant Betelgeuse in the CO first overtone lines with VLTI/AMBER|journal=Astronomy & Astrophysics |volume=529 |pages=A163 |year=2011 |last1=Ohnaka |first1=K.|last2=Weigelt |first2=G. |last3=Millour |first3=F. |last4=Hofmann |first4=K.-H. |last5=Driebe |first5=T. |last6=Schertl |first6=D. |last7=Chelli |first7=A. |last8=Massi |first8=F. |last9=Petrov |first9=R. |last10=Stee |first10=Ph. |bibcode=2011A&A...529A.163O |arxiv=1104.0958 |s2cid=56281923 }}</ref>{{efn|
"We derive a uniform-disk diameter of {{val|42.05|0.05|u=mas}} and a power-law-type limb-darkened disk diameter of {{val|42.49|0.06|u=mas}} and a limb-darkening parameter of {{val|9.7|0.5|e=−2}}"<ref name=OHNAKA2011/>
}} The near-infrared photospheric diameter of {{val|43.33|u=mas}} at the Hipparcos distance of {{val|152|20|u=pc}} equates to about {{val|3.4|u=AU}} or {{solar radius|730}}.<ref name="KERVELLA2011">{{cite journal|doi=10.1051/0004-6361/201116962|title=The close circumstellar environment of Betelgeuse|journal=Astronomy & Astrophysics |volume=531 |pages=A117 |year=2011 |last1=Kervella |first1=P. |last2=Perrin |first2=G. |last3=Chiavassa |first3=A. |last4=Ridgway |first4=S. T. |last5=Cami |first5=J. |last6=Haubois |first6=X. |last7=Verhoelst |first7=T.|arxiv=1106.5041|s2cid=119190969}}</ref> A 2014 paper derives an angular diameter of {{val|42.28|u=mas}} (equivalent to a {{val|41.01|u=mas}} uniform disc) using H and K band observations made with the VLTI AMBER instrument.<ref name=montarges>{{cite journal |last1=Montargès |first1=M. |last2=Kervella |first2=P. |last3=Perrin |first3=G. |last4=Ohnaka |first4=K. |last5=Chiavassa |first5=A. |last6=Ridgway |first6=S. T. |last7=Lacour |first7=S. |date=2014 |title=Properties of the CO and H2O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations |journal=Astronomy & Astrophysics |volume=572 |pages=id.A17 |bibcode=2014A&A...572A..17M |doi=10.1051/0004-6361/201423538 |arxiv=1408.2994 |s2cid=118419296}}</ref>

In 2009 it was announced that the radius of Betelgeuse had shrunk from 1993 to 2009 by 15%, with the 2008 angular measurement equal to {{val|47.0|u=mas}}.<ref name=TOWNES1/><ref name=COWEN>{{cite web
 | url=http://www.sciencenews.org/view/generic/id/44573/title/Betelgeuse_shrinks
 | title=Betelgeuse Shrinks: The Red Supergiant has Lost 15 Percent of its Size
 | date=10 June 2009
 | first=Ron
 | last=Cowen
 | quote=
 | archive-date=29 June 2011
 | archive-url=https://web.archive.org/web/20110629205838/http://www.sciencenews.org/view/generic/id/44573/title/Betelgeuse_shrinks
 | access-date=11 June 2009 | url-status=dead
}}
</ref>{{efn|
The shrinkage corresponds to the star contracting by a distance equal to that between Venus and the Sun, researchers reported June 9 at an American Astronomical Society meeting and in the June&nbsp;1 Astrophysical Journal Letters.<ref name=COWEN/>
}}
Unlike most earlier papers, this study used measurements at one specific wavelength over 15&nbsp;years. The diminution in Betelgeuse's [[apparent size]] equates to a range of values between {{val|56.0|0.1|u=mas}} seen in 1993 to {{val|47.0|0.1|u=mas}} seen in 2008— a contraction of almost {{val|0.9|u=AU}} in {{val|15|u=years}}.<ref name=TOWNES1/> The observed contraction is generally believed to be a variation in just a portion of the extended atmosphere around Betelgeuse, and observations at other wavelengths have shown an increase in diameter over a similar period.<ref name=montarges/>

The latest models of Betelgeuse adopt a photospheric angular diameter of around {{val|43|u=mas}}, with multiple shells out to 50–{{val|60|u=mas}}.<ref name=kervella2018/> Assuming a distance of {{val|197|u=pc}}, this means a stellar diameter of {{val|887|203|u=R_solar}}.<ref name=dolan2016/>

Once considered as having the largest angular diameter of any star in the sky after the [[Sun]], Betelgeuse lost that distinction in 1997 when a group of astronomers measured [[R Doradus]] with a diameter of {{val|57.0|0.5|u=mas}}, although R Doradus, being much closer to Earth at about {{val|200|u=ly}}, has a linear diameter roughly one-third that of Betelgeuse.<ref name=BEDDING>
{{cite journal
 | last1=Bedding |first1=T.R.
 | last2=Zijlstra  | first2=A.A.  | last3=von der Luhe  | first3=O.
 | last4=Robertson | first4=J.G.  | last5=Marson | first5=R.G.
 | last6=Barton    | first6=J.R.  | last7=Carter | first7=B.S.
 | year=1997
 | title=The angular diameter of R&nbsp;Doradus: A nearby Mira-like star
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=286  | issue=4  | pages=957–62
 | bibcode=1997MNRAS.286..957B | s2cid=15438522
 | arxiv = astro-ph/9701021
 | doi=10.1093/mnras/286.4.957  | doi-access=free
}}
</ref>

===Occultations===
[[File:Leona Betelgeuse.png|thumb|left|upright=1.35|Predicted path using SOLEX]]
Betelgeuse is too far from the ecliptic to be occulted by the major planets, but occultations by some [[asteroid]]s (which are more wide-ranging and much more numerous) occur frequently. A partial occultation by the 19th magnitude asteroid {{mp|(147857) 2005 UW|381}} occurred on 2 January 2012. It was partial because the angular diameter of the star was larger than that of the asteroid; the brightness of Betelgeuse dropped by only about 0.01 magnitudes.<ref name="occult">{{Cite web |last=Denissenko |first=Denis |date=3 October 2004 |title=Unique occultations |url=http://hea.iki.rssi.ru/~denis/special.html |archive-url=https://web.archive.org/web/20121216061951/http://hea.iki.rssi.ru/~denis/special.html |archive-date=16 December 2012}}</ref><ref>{{cite book |last=Hanslmeier |first=Arnold |title=Introduction to Astronomy and Astrophysics |year=2023 |isbn=978-3-662-64636-6 |pages=303–335 |chapter=State Variables of Stars |doi=10.1007/978-3-662-64637-3_8}}</ref>

The 14th magnitude asteroid [[319 Leona]] was predicted to occult on 12 December 2023, 01:12 UTC.<ref name="AT-20231209">{{cite news |last=Sigismondi |first=Costantino |date=9 December 2023 |title=The occultation of Betelgeuse by Leona: recovering the stellar surface brightness of a red supergiant, with a diffuse telescope, on Dec 12 1:12 UT |url=https://www.astronomerstelegram.org/?read=16374 |work=[[The Astronomer's Telegram]] |url-status=live |archiveurl=https://archive.today/20231212022447/https://www.astronomerstelegram.org/?read=16374 |archivedate=12 December 2023 |accessdate=11 December 2023 }}</ref> Totality was at first uncertain, and the occulation was projected to only last approximately twelve seconds (visible on a narrow path on Earth's surface, the exact width and location of which was initially uncertain due to lack of precise knowledge of the size and path of the asteroid).<ref>{{cite journal |last=Sigismondi |first=Costantino |year=2020 |title=The partial asteroidal occultation of Betelgeuse on Jan 2, 2012 |journal=Gerbertvs |volume=13 |page=25 |arxiv=1112.6398 |bibcode=2020Gerb...13...25S}}</ref> Projections were later refined as more data were analyzed for<ref>{{Cite web |title=IOTA-ES |url=https://www.iota-es.de/betelgeuse2023.html |access-date=2023-12-08 |website=www.iota-es.de}}</ref> a totality ("ring of fire") of approximately five seconds and a 60&nbsp;km wide path stretching from Tajikistan, Armenia, Turkey, Greece, Italy, Spain, the Atlantic Ocean, Miami, Florida and the [[Florida Keys]] to parts of Mexico.<ref>{{Cite news|url=https://www.theguardian.com/science/2023/dec/08/eclipse-betelgeuse-star-asteroid|title=Astronomers brace for rare eclipse as asteroid to pass in front of bright star|agency=Associated Press|date=8 December 2023|newspaper=The Guardian}}</ref> (The serendiptous event would also afford detailed observations of 319 Leona itself.)<ref>{{cite web |last=Hernandez |first=Joe |date=December 10, 2023 |title=A massive star called Betelgeuse will be briefly obscured by an asteroid Monday night |publisher=NPR |url=https://www.npr.org/2023/12/10/1218448190/a-massive-star-called-betelgeuse-will-be-briefly-obscured-by-an-asteroid-monday-}}</ref> Among other programmes 80 [[citizen science|amateur astronomers]] in Europe alone have been coordinated by astrophysicist [[Miguel Montargès]], et al. of the [[Paris Observatory]] for the event.<ref>{{cite web |last=Guenot |first=Marianne |date=Dec 7, 2023 |title=Betelgeuse, one of the brightest stars in the sky, will almost disappear next week. Here's how to see it. |website=[[MSN]] |url=https://www.msn.com/en-us/travel/news/betelgeuse-one-of-the-brightest-stars-in-the-sky-will-almost-disappear-next-week-heres-how-to-see-it/ar-AA1l9jJK |archive-url=https://web.archive.org/web/20231227010556/https://www.msn.com/en-us/travel/news/betelgeuse-one-of-the-brightest-stars-in-the-sky-will-almost-disappear-next-week-heres-how-to-see-it/ar-AA1l9jJK |archive-date=2023-12-27 |url-status=live}}</ref>

== Physical characteristics ==
[[File:Star-sizes.jpg|thumb|upright=1.85|(July 2008, outdated). Relative sizes of the planets in the [[Solar System]] and several stars, including Betelgeuse:
{{ordered list
| [[Mercury (planet)|Mercury]] < [[Mars]] < [[Venus]] < [[Earth]]
| [[Earth]] < [[Neptune]] < [[Uranus]] < [[Saturn]] < [[Jupiter]]
| [[Jupiter]] < [[Wolf 359]] < [[Sun]] < [[Sirius]]
| [[Sirius]] < [[Pollux (star)|Pollux]] < [[Arcturus]] < [[Aldebaran]]
| [[Aldebaran]] < [[Rigel]] < [[Antares]] < Betelgeuse
| Betelgeuse < [[Mu Cephei]] < [[VV Cephei A]] < [[VY Canis Majoris]]
}}
]]

Betelgeuse is a very large, luminous but cool star classified as an M1-2 Ia-ab [[red supergiant]]. The letter "M" in this designation means that it is a red star belonging to the [[Class M star|M spectral class]] and therefore has a relatively low photospheric temperature; the "Ia-ab" suffix [[Yerkes spectral classification scheme|luminosity class]] indicates that it is an intermediate-luminosity supergiant, with properties partway between a normal supergiant and a luminous supergiant. Since 1943, the spectrum of Betelgeuse has served as one of the stable anchor points by which other stars are classified.<ref name=baas25_1319>{{cite journal |last=Garrison |first=R.F. |year=1993 |title=Anchor points for the MK&nbsp;system of spectral classification |journal=[[Bulletin of the American Astronomical Society]] |volume=25 |page=1319 |bibcode=1993AAS...183.1710G |url=http://www.astro.utoronto.ca/~garrison/mkstds.html |access-date=4 February 2012 |archive-date=25 June 2019 |archive-url=https://web.archive.org/web/20190625094716/http://www.astro.utoronto.ca/~garrison/mkstds.html }}</ref>

Uncertainty in the star's surface temperature, diameter, and distance make it difficult to achieve a precise measurement of Betelgeuse's luminosity, but research from 2012 quotes a luminosity of around {{solar luminosity|126,000|link=y}}, assuming a distance of {{val|200|u=pc}}.<ref name=lebertre>{{cite journal |bibcode=2012MNRAS.422.3433L |arxiv=1203.0255 |title=Discovery of a detached H I gas shell surrounding {{nobr|{{mvar|α}} Orionis}} |journal=Monthly Notices of the Royal Astronomical Society |volume=422 |issue=4 |pages=3433 |last1=Le Bertre |first1=T. |last2=Matthews |first2=L. D.| last3=Gérard| first3=E.| last4=Libert| first4=Y. |year=2012 |doi=10.1111/j.1365-2966.2012.20853.x |doi-access=free |s2cid=54005037}}</ref> Studies since 2001 report effective temperatures ranging from 3,250 to 3,690 [[Kelvin|K]]. Values outside this range have previously been reported, and much of the variation is believed to be real, due to pulsations in the atmosphere.<ref name=dolan2016/> The star is also a slow rotator and the most recent velocity recorded was {{val|5.45|u=km/s}}<ref name=kervella2018/>—much slower than [[Antares]] which has a rotational velocity of {{val|20|u=km/s}}.<ref name="HR1">{{cite web |title=Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991) |work=[[VizieR]] |publisher=[[Centre de Données astronomiques de Strasbourg]] |url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%206134|access-date=7 September 2012}}</ref> The rotation period depends on Betelgeuse's size and orientation to Earth, but it has been calculated to take {{val|36|u=years}} to turn on its axis, inclined at an angle of around {{val|60|u=°}} to Earth.<ref name=kervella2018/>

In 2004, astronomers using computer simulations speculated that even if Betelgeuse is not rotating it might exhibit large-scale magnetic activity in its extended atmosphere, a factor where even moderately strong fields could have a meaningful influence over the star's dust, wind and mass-loss properties.<ref name=DORCH>
{{cite journal
 | last=Dorch |first=S.B.F.
 | year=2004
 | title=Magnetic activity in late-type giant stars: Numerical MHD simulations of non-linear dynamo action in Betelgeuse
 | journal=[[Astronomy & Astrophysics]]
 | volume= 423  | issue=3  | pages=1101–07
 | doi=10.1051/0004-6361:20040435
 | bibcode=2004A&A...423.1101D|arxiv = astro-ph/0403321 | s2cid=16240922
 | url=http://www.astro.ku.dk/~dorch/paper/copies/Dorch2004.pdf
}}
</ref>
A series of [[spectropolarimetry|spectropolarimetric]] observations obtained in 2010 with the [[Bernard Lyot Telescope]] at [[Pic du Midi Observatory]] revealed the presence of a weak magnetic field at the surface of Betelgeuse, suggesting that the giant convective motions of supergiant stars are able to trigger the onset of a small-scale [[dynamo effect]].<ref name="A&A516">
{{cite journal
 | last1=Aurière | first1=M. | last2=Donati | first2=J.-F.
 | last3=Konstantinova-Antova | first3=R. | last4=Perrin | first4=G.
 | last5=Petit | first5=P. | last6=Roudier | first6=T.
 | title=The magnetic field of Betelgeuse : A local dynamo from giant convection Cells?
 | year=2010
 | journal=[[Astronomy & Astrophysics]]
 | volume=516  | page=L2
 | arxiv=1005.4845  | bibcode=2010A&A...516L...2A
 | doi=10.1051/0004-6361/201014925
|s2cid=54943572 }}</ref>

===Mass===
Betelgeuse has no known orbital companions, so its mass cannot be calculated by that direct method. Modern mass estimates from theoretical modelling have produced values of {{Solar mass|9.5–21|link=y}},<ref name=NEILSON2011>
{{cite conference
 | last1=Neilson | first1=H.R.
 | last2=Lester | first2=J. B.
 | last3=Haubois | first3=X.
 | date=December 2011
 | title=Weighing Betelgeuse: Measuring the mass of {{nobr|{{mvar|α}} Orionis}} from stellar limb-darkening
 | journal=[[Astronomical Society of the Pacific]]
 | volume=451  | page = 117
 | conference=9th Pacific Rim Conference on Stellar Astrophysics. Proceedings of a conference held at Lijiang, China in 14–20 April 2011. ASP Conference Series
 | arxiv = 1109.4562
 | bibcode = 2011ASPC..451..117N
}}
</ref>
with values of {{solar mass|5}}–{{solar mass|30}} from older studies.<ref name=POSSON>
{{cite arXiv
 |last1=Posson-Brown |first1=Jennifer       |last2=Kashyap |first2=Vinay L.
 |last3=Pease        |first3=Deron O.       |last4=Drake   |first4=Jeremy J.
 |year=2006
 |title=Dark supergiant: Chandra's limits on X-rays from Betelgeuse
 |eprint=astro-ph/0606387
}}
</ref>
It has been calculated that Betelgeuse began its life as a star of {{solar mass|15–20}}, based on a solar luminosity of 90,000–150,000&nbsp;.<ref name=SMITH2009/> A novel method of determining the supergiant's mass was proposed in 2011, arguing for a current stellar mass of {{solar mass|11.6}} with an upper limit of 16.6 and lower of {{solar mass|7.7}}, based on observations of the star's intensity profile from narrow H-band interferometry and using a photospheric measurement of roughly {{val|4.3|u=AU}} or {{solar radius|{{val|955|217}}}}.<ref name=NEILSON2011/> A probabilistic age prior analysis give a current mass of {{solar mass|16.5–19}} and an initial mass of {{solar mass|18–21}}.<ref name=joyce2020/>

Betelgeuse's mass can also be estimated based on its position on the [[Hertzsprung–Russell diagram|color{{Nbh}}magnitude{{Nbh}}diagram&nbsp;(CMD)]]. Betelgeuse's color may have changed from yellow (or possibly orange; i.e. a yellow supergiant) to red in the last few thousand years, based on a 2022 review of historical records. This color change combined with the CMD suggest a mass of {{solar mass|14}}, an age of 14&nbsp;million year and a distance from 125 to 150&nbsp;parsecs (~400 to 500&nbsp;light years).<ref name=Neuhauser2022/>

=== Motion ===
[[File:Orion OB1 & 25 Ori Group.png|thumb|Map showing the Orion OB1 association, which contains the [[blue supergiants]] of [[Orion's Belt]] and the [[Orion Nebula]]. Betelgeuse is believed to be a runaway star that was ejected from the [[Orion OB1 association]].]]

The [[kinematics]] of Betelgeuse are complex. The age of class&nbsp;M supergiants with an initial mass of {{solar mass|20}} is roughly 10&nbsp;million years.<ref name=HARPER/><ref name=MAEDER>
{{cite conference
 | last1 = Maeder  | first1 = André
 | last2 = Meynet  | first2 = Georges
 | year = 2003
 | title = The role of rotation and mass loss in the evolution of massive stars
 | conference = IAU Symposium
 | volume = 212  | page = 267
 | bibcode = 2003IAUS..212..267M
}}
</ref>
Starting from its present position and motion, a projection back in time would place Betelgeuse around {{val|290|u=parsecs}} farther from the [[galactic plane]]—an implausible location, as there is no [[star formation]] [[Molecular cloud|region]] there. Moreover, Betelgeuse's projected pathway does not appear to intersect with the [[25 Orionis|25&nbsp;Ori]] [[Orion OB1 association|subassociation]] or the far younger Orion Nebula Cluster (ONC, also known as Ori OB1d), particularly since [[Very Long Baseline Array]] astrometry yields a distance from Betelgeuse to the ONC of between 389 and {{val|414|u=parsecs}}. Consequently, it is likely that Betelgeuse has not always had its current motion through space but has changed course at one time or another, possibly the result of a nearby [[Supernova|stellar explosion]].<ref name=HARPER/><ref name=REYNOLDS1>{{cite journal |doi=10.1086/157028 |bibcode=1979ApJ...229..942R |title=Optical evidence for a very large, expanding shell associated with the I Orion&nbsp;OB association, Barnard's loop, and the high galactic latitude H-alpha filaments in Eridanus |journal=The Astrophysical Journal |volume=229 |pages=942 |year=1979 |last1=Reynolds |first1=R.J. |last2=Ogden |first2=P.M. }}</ref> An observation by the [[Herschel Space Observatory]] in January 2013 revealed that the star's winds are crashing against the surrounding interstellar medium.<ref name=decin>{{cite journal |bibcode=2012A&A...548A.113D |arxiv=1212.4870 |title=The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure |journal=Astronomy & Astrophysics |volume=548 |pages=A113 |last1=Decin |first1=L. |last2=Cox |first2=N.L.J. |last3=Royer |first3=P. |last4=Van Marle |first4=A.J. |last5=Vandenbussche |first5=B. |last6=Ladjal |first6=D. |last7=Kerschbaum |first7=F. |last8=Ottensamer |first8=R. |last9=Barlow |first9=M.J. |last10=Blommaert |first10=J.A.D.L. |last11=Gomez |first11=H.L. |last12=Groenewegen |first12=M.A.T. |last13=Lim |first13=T. |last14=Swinyard |first14=B.M. |last15=Waelkens |first15=C. |last16=Tielens |first16=A.G.G.M. |year=2012 |doi=10.1051/0004-6361/201219792 |s2cid=53534124}}</ref>

The most likely star-formation scenario for Betelgeuse is that it is a runaway star from the [[Orion OB1 association]]. Originally a member of a high-mass multiple system within Ori OB1a, Betelgeuse was probably formed about 10–12&nbsp;million years ago,<ref>{{cite APOD |title=Orion: Head to Toe |date=23 October 2010 |access-date=8 October 2012}}</ref> but has evolved rapidly due to its high mass.<ref name="HARPER" /> H. Bouy and J. Alves suggested in 2015 that Betelgeuse may instead be a member of the newly discovered Taurion [[OB association]].<ref name=Buoy2015>{{cite journal |title=Cosmography of OB stars in the solar neighbourhood |last1=Bouy |first1=H. |last2=Alves |first2=J. |journal=Astronomy & Astrophysics |volume=584 |id=A26 |pages=13 |date=December 2015 |doi=10.1051/0004-6361/201527058 |bibcode=2015A&A...584A..26B |doi-access=free}}</ref>

=== Circumstellar dynamics ===
[[File:ESO-Betelgeuse.jpg|thumb|left|Image from [[ESO]]'s [[Very Large Telescope]] showing the stellar disk and an extended [[Stellar atmosphere|atmosphere]] with a previously unknown plume of surrounding gas]]

In the late phase of [[stellar evolution]], massive stars like Betelgeuse exhibit high rates of [[stellar mass loss|mass loss]], possibly as much as {{Solar mass|one}} every {{val|10,000|fmt=commas|u=years}}, resulting in a complex [[circumstellar envelope|circumstellar environment]] that is constantly in flux. In a 2009 paper, stellar mass loss was cited as the "key to understanding the evolution of the universe from the earliest cosmological times to the current epoch, and of planet formation and the formation of life itself".<ref name=RIDGEWAY>
{{cite journal
 | last1=Ridgway       | first1=Stephen        | last2=Aufdenberg | first2=Jason
 | last3=Creech-Eakman | first3=Michelle       | last4=Elias      | first4=Nicholas
 | last5=Howell        | first5=Steve          | last6=Hutter     | first6=Don
 | last7=Karovska      | first7=Margarita      | last8=Ragland    | first8=Sam
 | last9=Wishnow       | first9=Ed
 | display-authors=6
 | year=2009
 | title=Quantifying stellar mass loss with high angular resolution imaging
 | journal=Astronomy & Astrophysics
 | volume=247 | page=247
 | bibcode=2009astro2010S.247R
 |arxiv = 0902.3008
}}
</ref>
However, the physical mechanism is not well understood.<ref name=KERVELLA2011/> When [[Martin Schwarzschild]] first proposed his theory of huge convection cells, he argued it was the likely cause of mass loss in evolved supergiants like Betelgeuse.<ref name=SCHWARZSCHILD1975/> Recent work has corroborated this hypothesis, yet there are still uncertainties about the structure of their convection, the mechanism of their mass loss, the way dust forms in their extended atmosphere, and the conditions which precipitate their dramatic finale as a type II supernova.<ref name=KERVELLA2011/> In 2001, Graham Harper estimated a stellar wind at {{Solar mass|0.03}} every {{val|10,000|fmt=commas|u=years}},<ref name=HARPER2001>
{{cite journal
 | last1=Harper | first1=Graham M.
 | last2=Brown  | first2=Alexander
 | last3=Lim    | first3=Jeremy
 | date=April 2001
 | title=A spatially resolved, semiempirical model for the extended atmosphere of {{nobr|{{mvar|α}} Orionis}} (M2 Iab)
 | journal=The Astrophysical Journal
 | volume=551  | issue=2  | pages=1073–98
 | doi=10.1086/320215
 | bibcode=2001ApJ...551.1073H|s2cid=120271858 | doi-access=free
 }}</ref> but research since 2009 has provided evidence of episodic mass loss making any total figure for Betelgeuse uncertain.<ref name=OHNAKA2009/> Current observations suggest that a star like Betelgeuse may spend a portion of its lifetime as a [[Red supergiant star|red supergiant]], but then cross back across the H–R diagram, pass once again through a brief [[Yellow supergiant star|yellow supergiant]] phase and then explode as a [[blue supergiant]] or [[Wolf–Rayet star]].<ref name=LEVESQUE1>
{{cite conference
 | last=Levesque |first=E.M.
 | date=June 2010
 | title=The physical properties of red supergiants
 | publisher=[[Astronomical Society of the Pacific]]
 | conference = Hot and Cool: Bridging gaps in massive star evolution
 | series = ASP Conference Series
 | volume = 425   | page = 103
 | bibcode = 2010ASPC..425..103L | arxiv = 0911.4720
}}
</ref>
[[File:Betelgeuse Plume eso0927d.jpg|thumb|right|Artist's rendering from [[European Southern Observatory|ESO]] showing Betelgeuse with a gigantic bubble boiling on its surface and a radiant plume of gas being ejected to six photospheric radii or roughly the orbit of Neptune]]

Astronomers may be close to solving this mystery. They noticed a large plume of gas extending at least six times its stellar radius indicating that Betelgeuse is not shedding matter evenly in all directions.<ref name="KERVELLA2009" /> The plume's presence implies that the spherical symmetry of the star's photosphere, often observed in the infrared, is ''not'' preserved in its close environment. Asymmetries on the stellar disk had been reported at different wavelengths. However, due to the refined capabilities of the [[List of instruments at the Very Large Telescope|NACO]] adaptive optics on the VLT, these asymmetries have come into focus. The two mechanisms that could cause such asymmetrical mass loss, were large-scale convection cells or polar mass loss, possibly due to rotation.<ref name=KERVELLA2009/> Probing deeper with ESO's AMBER, gas in the supergiant's extended atmosphere has been observed vigorously moving up and down, creating bubbles as large as the supergiant itself, leading his team to conclude that such stellar upheaval is behind the massive plume ejection observed by Kervella.<ref name=OHNAKA2009>
{{cite journal
 | last1=Ohnaka  | first1=K.      | last2=Hofmann  | first2=K.-H.
 | last3=Benisty | first3=M.      | last4=Chelli   | first4=A.
 | last5=Driebe  | first5=T.      | last6=Millour  | first6=F.
 | last7=Petrov  | first7=R.      | last8=Schertl  | first8=D.
 | last9=Stee    | first9=Ph.
 | display-authors=6
 | year=2009
 | title=Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER
 | journal = [[Astronomy & Astrophysics]]
 | volume= 503 | issue=1 | pages=183–195
 | bibcode=2009A&A...503..183O
 | doi=10.1051/0004-6361/200912247
 | doi-access=free
 | arxiv = 0906.4792 | s2cid=17850433
}}
</ref>

==== Asymmetric shells ====
In addition to the photosphere, six other components of Betelgeuse's atmosphere have now been identified. They are a molecular environment otherwise known as the MOLsphere, a gaseous envelope, a chromosphere, a dust environment and two outer shells (S1 and S2) composed of [[carbon monoxide]] (CO). Some of these elements are known to be asymmetric while others overlap.<ref name=HAUBOIS/>
[[File:ESO Paranal Platform.jpg|thumb|left|Exterior view of ESO's Very Large Telescope ([[Very Large Telescope|VLT]]) in Paranal, Chile]]
At about 0.45 stellar radii (~2–{{val|3|u=AU}}) above the photosphere, there may lie a molecular layer known as the MOLsphere or molecular environment. Studies show it to be composed of water vapor and carbon monoxide with an effective temperature of about {{val|1500|500|u=K|fmt=commas}}.<ref name=HAUBOIS/><ref name=TSUJI>
{{cite journal
 | last=Tsuji | first=T.
 | year=2000
 | title=Water on the early M&nbsp;supergiant stars {{nobr|{{mvar|α}} Orionis}} and {{nobr|{{mvar|μ}} Cephei}}
 | journal=The Astrophysical Journal
 | volume=538 | issue=2 | pages=801–07
 | bibcode=2000ApJ...538..801T
 | doi=10.1086/309185 | doi-access=free
}}
</ref>
Water vapor had been originally detected in the supergiant's spectrum in the 1960s with the two Stratoscope projects but had been ignored for decades. The MOLsphere may also contain [[Silicon monoxide|SiO]] and [[Aluminium oxide|Al<sub>2</sub>O<sub>3</sub>]]—molecules which could explain the formation of dust particles.
[[File:Eso-paranal-16.jpg|thumb|left|Interior view of one of the four 8.2-meter Unit Telescopes at ESO's VLT]]

Another cooler region, the asymmetric gaseous envelope, extends for several radii (~10–{{val|40|u=AU}}) from the photosphere. It is enriched in oxygen and especially in [[nitrogen]] relative to carbon. These composition anomalies are likely caused by contamination by [[CNO cycle|CNO]]-processed material from the inside of Betelgeuse.<ref name=HAUBOIS/><ref name=LAMBERT>
{{cite journal
 | last1=Lambert | first1=D.L.      | last2=Brown   | first2=J.A.
 | last3=Hinkle  | first3=K.H.      | last4=Johnson | first4=H.R.
 | year=1984
 | title=Carbon, nitrogen, and oxygen abundances in Betelgeuse
 | journal=Astrophysical Journal
 | volume=284 | pages=223–37
 | bibcode=1984ApJ...284..223L
 | doi=10.1086/162401
}}</ref>

Radio-telescope images taken in 1998 confirm that Betelgeuse has a highly complex atmosphere,<ref name=NRAO/> with a temperature of {{val|3450|850|u=K|fmt=commas}}, similar to that recorded on the star's surface but much lower than surrounding gas in the same region.<ref name=NRAO>
{{cite press release
 |first=Dave |last=Finley
 |date=8 April 1998
 |title=VLA shows "boiling" in atmosphere of Betelgeuse
 |publisher=[[National Radio Astronomy Observatory]]
 |url=http://www.nrao.edu/pr/1998/betel/
 |access-date=7 September 2010
}}
</ref><ref name=LIM>
{{cite journal
 | title=Large Convection Cells as the Source of Betelgeuse's Extended Atmosphere
 | last1=Lim    | first1=Jeremy        | last2=Carilli | first2=Chris L.
 | last3=White  | first3=Stephen M.    | last4=Beasley | first4=Anthony J.
 | last5=Marson | first5=Ralph G.
 | year=1998
 | journal=[[Nature (journal)|Nature]]
 | volume=392  | issue=6676  | pages=575–577
 | bibcode=1998Natur.392..575L
 | doi=10.1038/33352
 |s2cid=4431516
}}
</ref> The VLA images also show this lower-temperature gas progressively cools as it extends outward. Although unexpected, it turns out to be the most abundant constituent of Betelgeuse's atmosphere. "This alters our basic understanding of red-supergiant star atmospheres", explained Jeremy Lim, the team's leader. "Instead of the star's atmosphere expanding uniformly due to gas heated to high temperatures near its surface, it now appears that several giant convection cells propel gas from the star's surface into its atmosphere."<ref name=NRAO/> This is the same region in which Kervella's 2009 finding of a bright plume, possibly containing carbon and nitrogen and extending at least six photospheric radii in the southwest direction of the star, is believed to exist.<ref name=HAUBOIS/>

The [[chromosphere]] was directly imaged by the Faint Object Camera on board the Hubble Space Telescope in ultraviolet wavelengths. The images also revealed a bright area in the southwest quadrant of the disk.<ref name=LOBEL2004/> The average radius of the chromosphere in 1996 was about 2.2&nbsp;times the optical disk (~{{val|10|u=AU}}) and was reported to have a temperature no higher than {{val|5500|u=K|fmt=commas}}.<ref name=HAUBOIS/><ref name=DUPREE>
{{cite journal
 | last1=Dupree    |first1=Andrea K.
 | last2=Gilliland |first2=Ronald L.
 | date=December 1995
 | title=HST direct image of Betelgeuse
 | journal=[[Bulletin of the American Astronomical Society]]
 | volume=27  | page=1328
 | bibcode=1995AAS...187.3201D
}}
</ref>{{efn|
"Such a major single feature is distinctly different from scattered smaller regions of activity typically found on the Sun although the strong ultraviolet flux enhancement is characteristic of stellar magnetic activity. This inhomogeneity may be caused by a large scale convection cell or result from global pulsations and shock structures that heat the chromosphere."<ref name=DUPREE/>
}}
However, in 2004 observations with the STIS, Hubble's high-precision spectrometer, pointed to the existence of warm chromospheric plasma at least one arcsecond away from the star. At a distance of {{val|197|u=pc}}, the size of the chromosphere could be up to {{val|200|u=AU}}.<ref name=LOBEL2004>
{{cite conference
 | last1=Lobel    |first1=A.          | last2=Aufdenberg |first2=J.
 | last3=Dupree   |first3=A.K.        | last4=Kurucz     |first4=R.L.
 | last5=Stefanik |first5=R.P.        | last6=Torres     |first6=G.
 | year=2004
 | title=Spatially resolved STIS spectroscopy of Betelgeuse's outer atmosphere
 | conference=219th Symposium of the IAU
 | page= 641
 | bibcode=2004IAUS..219..641L
 | volume=219
 | doi=10.1017/s0074180900182671
 | s2cid=15868906
 |arxiv = astro-ph/0312076
 | quote=
}}
</ref>{{efn|
"In the article, Lobel ''et al.'' equate 1&nbsp;arcsecond to approximately 40&nbsp;stellar radii, a calculation which in 2004 likely assumed a Hipparcos distance of 131&nbsp;pc (430&nbsp;ly) and a photospheric diameter of 0.0552″ from Weiner ''et al''."<ref name=LOBEL2004/>
}}
The observations have conclusively demonstrated that the warm chromospheric plasma spatially overlaps and co-exists with cool gas in Betelgeuse's gaseous envelope as well as with the dust in its circumstellar dust shells.<ref name="HAUBOIS" /><ref name=LOBEL2004/>

[[File:Nebula around Betelgeuse.jpg|thumb|This [[infrared]] image from the [[ESO]]'s [[Very Large Telescope|VLT]] shows complex shells of gas and dust around Betelgeuse – the [[:File:Nebula and betelgeuse VLT.jpg|tiny red circle]] in the middle is the size of the photosphere.]]

The first claim of a dust shell surrounding Betelgeuse was put forth in 1977 when it was noted that dust shells around mature stars often emit large amounts of radiation in excess of the photospheric contribution. Using [[Interferometry#Heterodyne detection|heterodyne interferometry]], it was concluded that the red supergiant emits most of its excess radiation from positions beyond 12 stellar radii or roughly the distance of the [[Kuiper belt]] at 50 to 60 AU, which depends on the assumed stellar radius.<ref name="SUTTON1977"/><ref name="HAUBOIS"/> Since then, there have been studies done of this dust envelope at varying wavelengths yielding decidedly different results. Studies from the 1990s have estimated the inner radius of the dust shell anywhere from 0.5 to {{val|1.0|ul=arcseconds}}, or 100 to {{val|200|u=AU}}.<ref name=SKINNER>
{{cite journal
 | last1=Skinner |first1=C.J.        | last2=Dougherty | first2=S.M.
 | last3=Meixner | first3=M.         | last4=Bode      | first4=M.F.
 | last5=Davis   | first5=R.J.       | last6=Drake     | first6=S.A.
 | last7=Arens   | first7=J.F.       | last8=Jernigan  | first8=J.G.
 | display-authors=6
 | year=1997
 | title=Circumstellar environments – V. The asymmetric chromosphere and dust shell of Alpha&nbsp;Orionis
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=288 | issue=2 | pages=295–306
 | bibcode=1997MNRAS.288..295S
 | doi=10.1093/mnras/288.2.295 | doi-access=free
}}
</ref><ref name=DANCHI>
{{cite journal
 | last1=Danchi    | first1=W.C.       | last2=Bester    | first2=M.
 | last3=Degiacomi | first3=C.G.       | last4=Greenhill | first4=L.J.
 | last5=Townes    | first5=C.H.
 | year=1994
 | title=Characteristics of dust shells around 13&nbsp;late-type stars
 | journal=The Astronomical Journal
 | volume=107 | issue=4 | pages=1469–1513
 | doi=10.1086/116960
 | bibcode=1994AJ....107.1469D
}}
</ref>
These studies point out that the dust environment surrounding Betelgeuse is not static. In 1994, it was reported that Betelgeuse undergoes sporadic decades-long dust production, followed by inactivity. In 1997, significant changes in the dust shell's morphology in one year were noted, suggesting that the shell is asymmetrically illuminated by a stellar radiation field strongly affected by the existence of photospheric hotspots.<ref name="SKINNER" /> The 1984 report of a giant asymmetric dust shell {{val|1|u=pc}} ({{val|206,265|fmt=commas|u=AU}}) has not been corroborated by recent studies, although another published the same year said that three dust shells were found extending four light-years from one side of the decaying star, suggesting that Betelgeuse sheds its outer layers as it moves.<ref name="BAUD">
{{cite journal
 | last1=Baud          | first1=B.        | last2=Waters    | first2=R.
 | last3=de&nbsp;Vries | first3=J.        | last4=van&nbsp;Albada | first4=G.D.
 | last5=Boulanger     | first5=F.        | last6=Wesselius | first6=P.R.
 | last7=Gillet        | first7=F.        | last8=Habing    | first8=H.J.
 | last9=van der Kruit | first9=P.C.
 | display-authors=6
 | date=January 1984
 | title=A giant asymmetric dust shell around Betelgeuse
 | journal=[[Bulletin of the American Astronomical Society]]
 | volume=16 | page=405
 | bibcode=1984BAAS...16..405B
}}
</ref><ref name=DAVID>
{{cite magazine
 | last1=David | first1=L.
 | last2=Dooling |first2=D.
 | year=1984
 | title=The Infrared Universe
 | magazine=Space World
 | issue=2
 | pages=4–7
 | bibcode=1984SpWd....2....4D
}}
</ref>

Although the exact size of the two outer [[carbon monoxide|CO]] shells remains elusive, preliminary estimates suggest that one shell extends from about 1.5 to 4.0&nbsp;[[arcseconds]] and the other expands as far as 7.0&nbsp;arcseconds.<ref name=HARPER2009>
{{cite journal
 | last1=Harper |first1=Graham M.  | last2=Carpenter  | first2=Kenneth G.
 | last3=Ryde | first3=Nils  | last4=Smith | first4=Nathan
 | last5=Brown | first5=Joanna  | last6=Brown  | first6=Alexander
 | last7=Hinkle | first7=Kenneth H. | last8=Stempels | first8=Eric
 | display-authors=6
  | year=2009
| title=UV, IR, and mm studies of CO surrounding the red supergiant {{nobr|{{mvar|α}} Orionis}} (M2 Iab)
 | journal=AIP Conference Proceedings
 | volume= 1094
 | pages=868–871
 | doi=10.1063/1.3099254
 | bibcode=2009AIPC.1094..868H
}}
</ref>
Assuming the Jovian orbit of {{val|5.5|u=AU}} as the star radius, the inner shell would extend roughly 50 to 150 stellar radii (~300 to {{val|800|u=AU}}) with the outer one as far as 250 stellar radii (~{{val|1,400|fmt=commas|u=AU}}). The Sun's [[heliopause (astronomy)|heliopause]] is estimated at 100 AU, so the size of this outer shell would be almost fourteen times the size of the Solar System.

==== Supersonic bow shock ====
Betelgeuse is travelling through the interstellar medium at a speed of {{val|30|u=km/second}} (i.e. ~{{val|6.3|u=AU/year}}) creating a [[Bow shocks in astrophysics|bow shock]].<ref name=MOHAMED1/><ref name=LAMERS1999>
{{cite book
 | last1=Lamers |first1=Henny J.G.L.M.
 | last2=Cassinelli |first2=Joseph P.
 | name-list-style=amp
 | date=June 1999
 | title=Introduction to Stellar Winds
 | publisher=Cambridge University Press
 | location=Cambridge, UK
 | isbn=978-0-521-59565-0
 | bibcode=1999isw..book.....L
}}
</ref>
The shock is not created by the star, but by its powerful [[stellar wind]] as it ejects vast amounts of gas into the interstellar medium at a speed of {{val|17|u=km/s}}, heating the material surrounding the star, thereby making it visible in infrared light.<ref name=ESA3>
{{cite press release
 |title=Akari Infrared Space Telescope: Latest science highlights
 |publisher=[[European Space Agency]]
 |url=http://www.esa.int/Our_Activities/Space_Science/Akari_infrared_space_telescope_latest_science_highlights
 |date=19 November 2008
 |access-date=25 June 2012
 |archive-url=https://web.archive.org/web/20110217144724/http://www.esa.int/esaSC/SEMCJT4DHNF_index_1.html
 |archive-date= 17 February 2011}}</ref> Because Betelgeuse is so bright, it was only in 1997 that the bow shock was first imaged. The [[comet]]ary structure is estimated to be at least one parsec wide, assuming a distance of 643&nbsp;light-years.<ref name=NORIEGA1>
{{cite journal
 | last1=Noriega-Crespo | first1=Alberto   | last2=van Buren | first2=Dave
 | last3=Cao        | first3=Yu            | last4=Dgani     | first4=Ruth
 | year=1997
 | title=A parsec-size bow shock around Betelgeuse
 | journal=[[Astronomical Journal]]
 | volume=114  | pages=837–40
 | bibcode=1997AJ....114..837N
 | doi=10.1086/118517  | doi-access=free
}}
</ref>{{efn|
"Noriega in 1997 estimated the size to be 0.8&nbsp;parsecs, having assumed the earlier distance estimate of 400 ly. With a current distance estimate of 643&nbsp;ly, the bow shock would measure ~1.28 parsecs or over 4&nbsp;ly."<ref name=NORIEGA1/>
}}

[[Fluid dynamics|Hydrodynamic]] simulations of the bow shock made in 2012 indicate that it is very young—less than 30,000&nbsp;years old—suggesting two possibilities: That Betelgeuse moved into a region of the interstellar medium with different properties only recently or that Betelgeuse has undergone a significant transformation producing a changed stellar wind.<ref name=ASTROBITES1>
{{cite web
 |last=Newton |first=Elizabeth
 |date=26 April 2012
 |title=This star lives in exciting times, or, how did Betelgeuse make that funny shape?
 |website=Astrobites (astrobites.com)
 |url=http://astrobites.com/2012/04/26/this-star-lives-in-exciting-times-or-how-did-betelgeuse-make-that-funny-shape/
 |access-date=25 June 2012  |url-status=dead
 |archive-url=https://web.archive.org/web/20120430035007/http://astrobites.com/2012/04/26/this-star-lives-in-exciting-times-or-how-did-betelgeuse-make-that-funny-shape/
 |archive-date=30 April 2012
}}
</ref>
A 2012 paper, proposed that this phenomenon was caused by Betelgeuse transitioning from a [[blue supergiant]] (BSG) to a red supergiant (RSG). There is evidence that in the late evolutionary stage of a star like Betelgeuse, such stars "may undergo rapid transitions from red to blue and vice versa on the Hertzsprung–Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks."<ref name="MOHAMED1">{{cite journal
 | last1=Mohamed |first1=S.
 | last2=Mackey |first2=J.
 | last3=Langer |first3=N.
 | year=2012
 | title=3D simulations of Betelgeuse's bow shock
 | journal=[[Astronomy & Astrophysics]]
 | volume= 541  | page=A1
 | bibcode=2012A&A...541A...1M
 | doi=10.1051/0004-6361/201118002
 | arxiv=1109.1555  | s2cid=118435586
}}
</ref><ref name=MACKEY1>
{{cite journal
 | last1=MacKey  | first1=Jonathan     | last2=Mohamed | first2=Shazrene
 | last3=Neilson | first3=Hilding R.   | last4=Langer  | first4=Norbert
 | last5=Meyer   | first5=Dominique M.-A.
 | year=2012
 | title=Double bow shocks around young, runaway red supergiants: Application to Betelgeuse
 | journal=The Astrophysical Journal
 | volume=751  | issue=1  | page=L10
 | bibcode=2012ApJ...751L..10M
 | doi=10.1088/2041-8205/751/1/L10
 | arxiv = 1204.3925  | s2cid=118433862
}}</ref> Moreover, if future research bears out this hypothesis, Betelgeuse may prove to have traveled close to 200,000 AU as a red supergiant scattering as much as {{val|3|u=M_solar}} along its trajectory.

==Life phases==
Betelgeuse is a red supergiant that has evolved from an [[O-type main-sequence star]]. After core hydrogen exhaustion, Betelgeuse evolved into a blue supergiant before evolving into its current red supergiant form.<ref name="vanloon" /> Its core will eventually collapse, producing a [[supernova]] explosion and leaving behind a compact [[supernova remnant|remnant]]. The details depend on the exact initial mass and other physical properties of that main sequence star.

===Main sequence===
[[File:Hertzsprung-Russell Diagram - ESO.png|thumb|right|[[Hertzsprung–Russell diagram]] identifying supergiants like Betelgeuse that have moved off the [[main sequence]]]]

The initial mass of Betelgeuse can only be estimated by testing different stellar evolutionary models to match its current observed properties. The unknowns of both the models and the current properties mean that there is considerable uncertainty in Betelgeuse's initial appearance, but its mass is usually estimated to have been in the range of {{solar mass|10–25}}, with modern models finding values of {{solar mass|15–20}}. Its chemical makeup can be reasonably assumed to have been around 70% hydrogen, 28% helium, and 2.4% heavy elements, slightly more metal-rich than the Sun but otherwise similar. The initial rotation rate is more uncertain, but models with slow to moderate initial rotation rates produce the best matches to Betelgeuse's current properties.<ref name=dolan2016/><ref name=vanloon/><ref name=meynet>{{cite conference |title=The past and future evolution of a star like Betelgeuse |book-title=Betelgeuse Workshop 2012 |editor=P. Kervella |volume=60 |pages=17–28 |last1=Meynet |first1=G. |last2=Haemmerlé |first2=L. |last3=Ekström |first3=S. |last4=Georgy |first4=C. |last5=Groh |first5=J. |last6=Maeder |first6=A. |year=2013 |bibcode=2013EAS....60...17M |arxiv=1303.1339 |doi=10.1051/eas/1360002 |citeseerx=10.1.1.759.5862 |s2cid=119111572}}</ref> That main sequence version of Betelgeuse would have been a hot luminous star with a spectral type such as O9V.<ref name=lebertre/>

A {{solar mass|15}} star would take between 11.5 and 15&nbsp;million years to reach the red supergiant stage, with more rapidly-rotating stars taking the longest.<ref name=meynet/> Rapidly-rotating {{solar mass|20}} stars take 9.3&nbsp;million years to reach the red supergiant stage, while {{solar mass|20}} stars with slow rotation take only 8.1&nbsp;million years.<ref name=vanloon/> These are the best estimates of Betelgeuse's current age, as the time since its [[Main sequence|zero age main sequence]] stage is estimated to be 8.0–8.5&nbsp;million years as a {{solar mass|20}} star with no rotation.<ref name=dolan2016/>

=== After core hydrogen exhaustion ===
Betelgeuse's time spent as a red supergiant can be estimated by comparing mass loss rates to the observed circumstellar material, as well as the abundances of heavy elements at the surface. Estimates range from 10,000&nbsp;years to a maximum of 140,000&nbsp;years. Betelgeuse appears to undergo short periods of heavy mass loss and is a runaway star moving rapidly through space, so comparisons of its current mass loss to the total lost mass are difficult.<ref name=dolan2016/><ref name=vanloon/>

[[File:O-type star.png|thumb|This is what Betelgeuse may have looked like up until about 1 million years ago, when it was a main-sequence star.]]
The surface of Betelgeuse shows enhancement of nitrogen, relatively low levels of carbon, and a high proportion of [[carbon-13|<sup>13</sup>C]] relative to [[carbon-12|<sup>12</sup>C]], all indicative of a star that has experienced the [[dredge-up|first dredge-up]]. However, the first dredge-up occurs soon after a star reaches the red supergiant phase and so this only means that Betelgeuse has been a red supergiant for at least a few thousand years. The best prediction is that Betelgeuse has already spent around 40,000&nbsp;years as a red supergiant,<ref name=dolan2016/> having left the main sequence perhaps one million years ago.<ref name=meynet/>

The current mass can be estimated from evolutionary models from the initial mass and the expected mass lost so far. For Betelgeuse, the total mass lost is predicted to be no more than about {{solar mass|one}}, giving a current mass of {{solar mass|19.4–19.7}}, considerably higher than estimated by other means such as pulsational properties or limb-darkening models.<ref name=dolan2016/>

[[File:Betelgeuse supernova.png|thumb|right|[[Celestia]] depiction of Orion as it might appear from Earth when Betelgeuse explodes as a [[supernova]], which could be brighter than the supernova that exploded in 1006 ([[SN 1006]])]]
All stars more massive than about {{solar mass|10}} are expected to end their lives when their cores collapse, typically producing a supernova explosion. Up to about {{solar mass|15}}, a type&nbsp;II-P supernova is always produced from the red supergiant stage.<ref name="meynet" />

More massive stars can lose mass quickly enough that they evolve towards higher temperatures before their cores can collapse, particularly for rotating stars and models with especially high mass loss rates. These stars can produce type&nbsp;II-L or type&nbsp;IIb supernovae from yellow or blue supergiants, or type I&nbsp;b/c supernovae from Wolf–Rayet stars.<ref name=groh2013>
{{cite journal
 |last1= Groh |first1= Jose H. |last2= Meynet |first2= Georges
 |last3= Georgy |first3= Cyril |last4= Ekstrom |first4= Sylvia
 |year= 2013
 |title= Fundamental properties of core-collapse supernova and GRB progenitors: Predicting the look of massive stars before death
 |journal= Astronomy & Astrophysics
 |volume= 558 |pages= A131
 |doi= 10.1051/0004-6361/201321906 |arxiv=1308.4681
 |bibcode=2013A&A...558A.131G |s2cid= 84177572
}}
</ref> Models of rotating {{solar mass|20}} stars predict a peculiar type&nbsp;II supernova similar to [[SN 1987A]] from a [[blue supergiant]] progenitor.<ref name=meynet/> On the other hand, non-rotating {{solar mass|20}} models predict a type&nbsp;II-P supernova from a red [[supergiant]] progenitor.<ref name="dolan2016" />

The time until Betelgeuse explodes depends on the predicted initial conditions and on the estimate of the time already spent as a red supergiant. The total lifetime from the start of the red supergiant phase to core collapse varies from about 300,000&nbsp;years for a rotating {{solar mass|25}} star, 550,000&nbsp;years for a rotating {{solar mass|20}} star, and up to a million years for a non-rotating {{solar mass|15}} star. Given the estimated time since Betelgeuse became a red supergiant, estimates of its remaining lifetime range from a "best guess" of under 100,000&nbsp;years for a non-rotating {{solar mass|20}} model to far longer for rotating models or lower-mass stars.<ref name=dolan2016/><ref name=meynet/> Betelgeuse's suspected birthplace in the [[Orion OB1 association]] is the location of several previous supernovae. It is believed that runaway stars may be caused by supernovae, and there is strong evidence that [[OB star]]s [[Mu Columbae|μ&nbsp;Columbae]], [[AE Aurigae]], and [[53 Arietis]] all originated from such explosions in Ori&nbsp;OB1 2.2, 2.7, and 4.9&nbsp;million years ago.<ref name=REYNOLDS1/>

A typical type&nbsp;II-P [[supernova]] emits {{val|2|e=46|ul=J}} of [[neutrino]]s and produces an explosion with a kinetic energy of {{val|2|e=44|u=J}}. As seen from Earth, Betelgeuse as a type&nbsp;II-P supernova would have a peak apparent magnitude somewhere in the range −8 to −12.<ref>
{{cite journal
 |last1=Goldberg |first1=Jared A.
 |last2=Bauer |first2=Evan B.
 |last3=Howell |first3=D. Andrew
 |year=2020
 |title=Apparent magnitude of Betelgeuse as a type II-P supernova
 |journal=Research Notes of the AAS
 |volume=4 |issue=3 |pages=35
 |doi=10.3847/2515-5172/ab7c68
 |bibcode=2020RNAAS...4...35G |s2cid=216398511
|doi-access=free
 }}
</ref> This would be easily visible in daylight, with a possible brightness up to a significant fraction of the [[full moon]], though likely not exceeding it. This type of supernova would remain at roughly constant brightness for 2–3&nbsp;months before rapidly dimming. The visible light is produced mainly by the radioactive decay of [[cobalt]], and sustains its brightness due to the increasing transparency of the cooling hydrogen ejected by the supernova.<ref name=wheeler>
{{cite book
 | last=Wheeler | first=J. Craig
 | year=2007
 | title=Cosmic Catastrophes: Exploding stars, black holes, and mapping the universe
 | publisher=Cambridge University Press
 | location=Cambridge, UK
 | edition=2nd
 | isbn=978-0-521-85714-7
 | pages=115–117
 | url=https://www.cambridge.org/core/books/cosmic-catastrophes/E68477687EFB37E52EBE00246AC203FC
 | doi=10.1017/CBO9780511536625.007
 | url-access=limited
}}
</ref>

====Media reporting====
Due to misunderstandings caused by the 2009 publication of the star's 15% contraction, apparently of its outer atmosphere,<ref name=UCBERKELEY2009/><ref name=ASTRONOMYMAG2009/> Betelgeuse has frequently been the subject of scare stories and rumors suggesting that it will explode within a year, and leading to exaggerated claims about the consequences of such an event.<ref>
{{cite news
 | last=Connelly | first=Claire
 | date=19 January 2011
 | title=Tatooine's twin suns – coming to a planet near you just as soon as Betelgeuse explodes
 | website=News.com.au
 | url=http://www.news.com.au/technology/sci-tech/tatooines-twin-suns-coming-to-a-planet-near-you-just-as-soon-as-betelgeuse-explodes/story-fn5fsgyc-1225991009247
 | access-date=14 September 2012 | url-status=dead
 | archive-url=https://web.archive.org/web/20120922083805/http://www.news.com.au/technology/sci-tech/tatooines-twin-suns-coming-to-a-planet-near-you-just-as-soon-as-betelgeuse-explodes/story-fn5fsgyc-1225991009247
 | archive-date=22 September 2012 | df=dmy-all
}}
</ref><ref>{{cite web
 | last=Plait
 | first=Phil
 | date=1 June 2010
 | title=Is Betelgeuse about to blow?
 | website=Bad Astronomy
 | publisher=Discovery
 | url=http://blogs.discovermagazine.com/badastronomy/2010/06/01/is-betelgeuse-about-to-blow/
 | access-date=14 September 2012
 | archive-date=21 April 2011
 | archive-url=https://web.archive.org/web/20110421003143/http://blogs.discovermagazine.com/badastronomy/2010/06/01/is-betelgeuse-about-to-blow/
 | url-status=dead
 }}</ref> The timing and prevalence of these rumors have been linked to broader misconceptions of astronomy, particularly to doomsday predictions relating to the [[2012 phenomenon|Mayan calendrical apocalypse]].<ref>
{{cite news
 | last=O'Neill | first=Ian
 | date=20 January 2011
 | title=Don't panic! Betelgeuse won't explode in 2012!
 | website=Discovery space news
 | url=http://news.discovery.com/space/betelgeuse-probably-wont-explode-in-2012.htm
 | access-date=14 September 2012
 | archive-url=https://web.archive.org/web/20110123082459/http://news.discovery.com/space/dont-panic-betelgeuse-wont-explode-in-2012.html
 | archive-date=23 January 2011
}}
</ref><ref>{{cite web
 | last=Plait
 | first=Phil
 | date=21 January 2011
 | title=Betelgeuse and 2012
 | website=Bad Astronomy
 | publisher=Discovery
 | url=http://blogs.discovermagazine.com/badastronomy/2011/01/21/betelgeuse-and-2012/
 | access-date=14 September 2012
 | archive-date=3 November 2012
 | archive-url=https://web.archive.org/web/20121103082609/http://blogs.discovermagazine.com/badastronomy/2011/01/21/betelgeuse-and-2012/
 | url-status=dead
 }}</ref> Betelgeuse is not likely to produce a [[gamma-ray burst]] and is not close enough for its [[X-ray]]s, ultraviolet radiation, or ejected material to cause significant effects on [[Earth]].<ref name=dolan2016/><ref>{{Cite web |last=Betz |first=Eric |date=2020-02-14 |title=When Betelgeuse goes supernova, what will it look like from Earth? |url=https://www.astronomy.com/science/when-betelgeuse-goes-supernova-what-will-it-look-like-from-earth/ |access-date=2023-06-15 |website=Astronomy Magazine |language=en-US}}</ref>

Following the dimming of Betelgeuse in December&nbsp;2019,<ref name=AT-20191208>{{cite news |last1=Guinan |first1=Edward F. |author-link1=Edward Guinan |last2=Wasatonic |first2=Richard J. |last3=Calderwood |first3=Thomas J. |title=ATel #13341 – The fainting of the nearby red supergiant Betelgeuse |url=http://www.astronomerstelegram.org/?read=13341 |date=8 December 2019 |work=[[The Astronomer's Telegram]] |access-date=27 December 2019}}</ref><ref name=AT-20191223/> reports appeared in the science and mainstream media that again included speculation that the star might be about to explode as a supernova – even in the face of scientific research that a supernova is not expected for perhaps 100,000&nbsp;years.<ref name=Sep2014-Slate>
{{cite magazine
 |first = Phil |last = Plait |author-link = Phil Plait
 |date = 8 September 2014
 |title = When will Betelgeuse explode?
 |magazine = [[Slate (magazine)|Slate]]
 |url = https://slate.com/technology/2014/09/betelgeuse-astronomers-give-it-100000-years-before-it-explodes.html
 |access-date = 28 December 2019
}}
</ref> Some outlets reported the magnitude as faint as +1.3 as an unusual and interesting phenomenon, like ''Astronomy'' magazine,<ref name=Dec2019-AstroMag/> the ''[[National Geographic]]'',<ref name=NG-20191226/> and the [[Smithsonian (magazine)|''Smithsonian'']].<ref>
{{cite news
 |first = Katherine J. |last = Wu
 |date = 26 December 2019
 |title = A giant star is dimming, which could be a sign it is about to explode
 |magazine = [[Smithsonian (magazine)|Smithsonian]]
 |url = https://www.smithsonianmag.com/smart-news/giant-star-betelgeuse-dimming-sign-it-could-explode-180973861/
 |access-date = 28 December 2019
}}
</ref>

Some mainstream media, like ''[[The Washington Post]]'',<ref name=Dec2019-WaPo/> ''[[ABC News (Australia)|ABC News]]'' in Australia,<ref name=Dec2019-ABC/> and ''[[Popular Science]]'',<ref>
{{cite news
 |first = Rachel |last = Feltman
 |date = 26 December 2019
 |title = We really don't know when Betelgeuse is going to explode
 |magazine = [[Popular Science]]
 |url = https://www.popsci.com/story/space/betelgeuse-star-supernova/
 |access-date = 28 December 2019
}}
</ref> reported that a supernova was possible but unlikely, whilst other outlets falsely portrayed a supernova as an imminent realistic possibility. [[CNN]], for example, chose the headline "A giant red star is acting weird and scientists think it may be about to explode",<ref name=Dec2019-CNN>
{{cite news
 |first = Ryan |last = Prior
 |date = 26 December 2019
 |title = A giant red star is acting weird and scientists think it may be about to explode
 |website = [[CNN]]
 |url = https://edition.cnn.com/2019/12/26/world/betelgeuse-may-explode-scn-trnd/index.html
 |access-date = 28 December 2019
}}
</ref> while the ''[[New York Post]]'' declared Betelgeuse as "due for explosive supernova".<ref name=Dec2019-NYP>
{{cite news
 |first = Hannah |last = Sparks
 |date = 26 December 2019
 |title = Massive 'Betelgeuse' star in Orion constellation due for explosive supernova
 |newspaper = [[New York Post]]
 |url = https://nypost.com/2019/12/26/massive-betelgeuse-star-in-orion-constellation-due-for-explosive-supernova/
 |access-date = 28 December 2019
}}
</ref>

[[Phil Plait]], in his ''[[Bad Astronomy]]'' blog, noting that Betelgeuse's recent behaviour, "[w]hile unusual . . . isn't unprecedented," argued that the star is not likely to explode "for a long, long time."<ref name = Dec2019-SciFiWire>
{{cite web
 |first = Phil |last = Plait |author-link = Phil Plait
 |date = 24 December 2019
 |title = Don't Panic! Betelgeuse is (almost certainly) not about to explode
 |website = [[Syfy#Syfy Wire|Syfy Wire]]
 |url = https://www.syfy.com/syfywire/dont-panic-betelgeuse-is-almost-certainly-not-about-to-explode
 |access-date = 28 December 2019
}}
</ref> [[Dennis Overbye]] of ''[[The New York Times]]'' agreed that an explosion was not imminent but added that "astronomers are having fun thinking about it."<ref name=NYT-20200109>
{{cite news
 |last=Overbye |first=Dennis |author-link=Dennis Overbye
 |date=9 January 2020
 |title=Just a fainting spell? Or is Betelgeuse about to blow? – A familiar star in the constellation Orion has dimmed noticeably since October. Astronomers wonder if its explosive finale is imminent
 |newspaper=[[The New York Times]]
 |url=https://www.nytimes.com/2020/01/09/science/astronomy-supernova-betelgeuse.html
 |access-date=12 January 2020
}}
</ref>

Following the eventual supernova, [[Compact star|a small dense remnant]] will be left behind, either a [[neutron star]] or [[black hole]]. Betelgeuse does not seem to have a core massive enough for a black hole, so the remnant will probably be a neutron star of approximately {{solar mass|1.5}}.<ref name=dolan2016/>

== Binarity ==
Betelgeuse generally has been considered to be a single isolated star and a [[runaway star]], not currently associated with any cluster or star-forming region, although its birthplace is unclear.<ref name=vanloon>{{cite journal |bibcode=2013EAS....60..307V |title=Betelgeuse and the Red Supergiants |journal=Betelgeuse Workshop 2012 |editor-first=P. |editor-last=Kervella |volume=60 |pages=307–316 |last1=Van Loon |first1=J. Th. |year=2013 |doi=10.1051/eas/1360036 |arxiv=1303.0321 |citeseerx=10.1.1.759.580 |s2cid=118626509}}</ref> However, starting in 1985, three studies have proposed companion stars to Betelgeuse. In 1985, analysis of [[Polarization (waves)|polarization]] data from 1968 through 1983 indicated a close companion with a periodic orbit of about 2.1&nbsp;years, and by using [[Speckle imaging|speckle interferometry]], the team concluded that the closer of the two companions was located at {{val|0.06|0.01|u="}} (≈9&nbsp;AU) from the main star with a position angle of 273°, an orbit that would potentially place it within the star's [[chromosphere]]. The more distant companion was at {{val|0.51|0.01|u="}} (≈77&nbsp;AU) with a position angle of 278°.<ref name=KAROVSKA1>{{cite journal| title=On a possible close companion to {{nobr|{{mvar|α}} Ori}} | author1=Karovska, M. | author2=Noyes, R.W.| author3=Roddier, F. | author4=Nisenson, P.| author5=Stachnik, R.V.| journal=Bulletin of the American Astronomical Society| volume=17| page=598| year=1985| bibcode=1985BAAS...17..598K}}</ref><ref name=KAROVSKA2>{{cite journal| title=On the alpha Orionis triple system| author1=Karovska, M.| author2=Nisenson, P.| author3=Noyes, R.| journal=Astrophysical Journal| volume=308 | pages=675–85| year=1986| doi=10.1086/164497| bibcode=1986ApJ...308..260K}}</ref> Other studies have found no evidence for these companions or have actively refuted their existence,<ref name="WILSON2">{{cite journal| title=High-resolution imaging of Betelgeuse and Mira| author1=Wilson, R. W.| author2=Baldwin, J. E.| author3=Buscher, D. F.| author4=Warner, P. J.| journal=Monthly Notices of the Royal Astronomical Society| volume=257 | issue=3 | pages=369–76| year=1992| bibcode=1992MNRAS.257..369W| doi=10.1093/mnras/257.3.369 | doi-access=free}}</ref> but the possibility of a close companion contributing to the overall flux has never been fully ruled out.<ref name="HAUBOIS"/> High-resolution interferometry of Betelgeuse and its vicinity, far beyond the technology of the 1980s and 1990s, has not detected any companions.<ref name=KERVELLA2009/><ref name=montarges2016/>

More recently, in 2024, two studies found evidence for a companion star. One study found that a not yet directly-observed, dust-modulating star or [[compact object]] of {{val|1.17|0.07|ul=Solar mass}} at a distance of {{val|8.60|0.33}}&nbsp;[[Astronomical unit|AU]] would be the most likely solution for Betelgeuse's 2170-day secondary periodicity, fluctuating radial velocity, moderate radius and low variation in effective temperature.<ref name="Goldberg2024">
{{Cite journal |last1=Goldberg |first1=Jared A. |last2=Joyce |first2=Meridith |last3=Molnár |first3=László |date=November 2024 |title=A buddy for Betelgeuse: Binarity as the origin of the long secondary period in {{nobr|{{mvar|α}} Orionis}} |journal=The Astrophysical Journal |language=en |volume=977 |issue=1 |pages=35 |doi=10.3847/1538-4357/ad87f4 |doi-access=free |arxiv=2408.09089 |bibcode=2024ApJ...977...35G |issn=0004-637X}}</ref> A second study produced by a different group of researchers examined observational data spanning a century, also suggesting a close-in stellar companion, possibly less massive and luminous than the Sun with an orbital period of 5.78 years. It is expected to be engulfed by Betelgeuse within 10,000 years.<ref name=MacLeod2024>{{cite journal |last1=MacLeod |first1=Morgan |last2=Blunt |first2=Sarah |last3=De Rosa |first3=Robert J. |last4=Dupree |first4=Andrea K. |last5=Granzer |first5=Thomas |last6=Harper |first6=Graham M. |last7=Huang |first7=Caroline D. |last8=Leiner |first8=Emily M. |last9=Loeb |first9=Abraham |last10=Nielsen |first10=Eric L. |last11=Strassmeier |first11=Klaus G. |last12=Wang |first12=Jason J. |last13=Weber |first13=Michael |title=Radial Velocity and Astrometric Evidence for a Close Companion to Betelgeuse |journal=The Astrophysical Journal |date=2024 |volume=978 |issue=1 |page=50 |doi=10.3847/1538-4357/ad93c8 |doi-access=free |bibcode=2025ApJ...978...50M |arxiv=2409.11332 }}</ref>

In 2025, two studies based on X-ray observations exclude the possibility the companion is a compact star, suggesting it is likely a low-mass [[young stellar object]].<ref name=Goldberg2025>{{Cite arXiv |last1=Goldberg |first1=Jared A. |last2=O'Grady |first2=Anna J. G. |last3=Joyce |first3=Meridith |last4=Johnson |first4=Christian I. |last5=Molnár |first5=László |last6=Dupree |first6=Andrea |last7=O'Connor |first7=Brendan |last8=Drout |first8=Maria R. |last9=Moe |first9=Maxwell |title=Betelgeuse, Betelgeuse, Betelgeuse, Betel-buddy? Constraints on the dynamical companion to α Orionis from HST |date=2025-05-23 |class=astro-ph.SR |eprint=2505.18375 }}</ref><ref name=Grady2025>{{cite arXiv|eprint=2505.18376 |last1=O'Grady |first1=Anna J. G. |last2=O'Connor |first2=Brendan |last3=Goldberg |first3=Jared A. |last4=Joyce |first4=Meridith |last5=Molnár |first5=László |last6=Johnson |first6=Christian I. |last7=Hare |first7=Jeremy |last8=Breivik |first8=Katelyn |last9=Drout |first9=Maria R. |last10=Moe |first10=Maxwell |last11=Calamida |first11=Annalisa |title=Betelgeuse's Buddy: X-Ray Constraints on the Nature of $α$ Ori B |date=2025 |class=astro-ph.SR }}</ref> Such objects have X-ray luminosities comparable with those observed in Betelgeuse.<ref name=Grady2025/> The mass of the companion should be less than {{solar mass|1.5}}, and is more likely less than {{solar mass|1}}.<ref name=Goldberg2025/>

== Ethnological attributes ==

=== Spelling and pronunciation ===
Betelgeuse has also been spelled ''Betelgeux''<ref name="OED">{{Cite encyclopedia
 | title=Betelgeuse
 | encyclopedia=Oxford English Dictionary
 |editor1=Simpson, J. |editor2=Weiner, E. | year=1989
 | edition= 2nd
 | page=130
 | location=Oxford
 | publisher=Clarendon Press
 | isbn= 978-0-19-861186-8}}</ref> and, in [[German language|German]], ''Beteigeuze''{{efn|Likely the result of mistaking the '''l''' for an '''i'''. Ultimately, this led to the modern "Betelgeuse".}} (according to [[Johann Elert Bode|Bode]]).<ref>[[Johann Elert Bode|Bode, Johann Elert]], (ed.). (1782) ''Vorstellung der Gestirne: auf XXXIV Kupfertafeln nach der Parisier Ausgabe des Flamsteadschen Himmelsatlas'', Gottlieb August Lange, Berlin / [[Stralsund]], pl. XXIV.</ref><ref>[[Johann Elert Bode|Bode, Johann Elert]], (ed.) (1801). ''Uranographia: sive Astrorum Descriptio'', Fridericus de Harn, Berlin, pl. XII.</ref> ''Betelgeux'' and ''Betelgeuze'' were used until the early 20th century, when the spelling ''Betelgeuse'' became universal.<ref name="schaaf">{{cite book
 |author=Schaaf, Fred
 |year=2008
 |title=The Brightest Stars
 |url=https://archive.org/details/brighteststarsdi00scha
 |url-access=limited
 |chapter=Betelgeuse
 |pages=[https://archive.org/details/brighteststarsdi00scha/page/n182 174]–82
 |publisher=Wiley
 |location=Hoboken, New Jersey
 |isbn=978-0-471-70410-2}}</ref><!-- cites previous two sentences -->
Consensus on its pronunciation is weak and is as varied as its spellings:
* {{IPAc-en|ˈ|b|ɛ|t|əl|dʒ|uː|z}} {{respell|BET|əl-jooz}}{{snd}}[[Oxford English Dictionary]]<ref name="OED" /> and [[Royal Astronomical Society of Canada]]
* {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|z|,_|-|dʒ|ɜː|z}} {{respell|BEE|təl|jooz|,_-|jurz}}{{snd}}[[Oxford English Dictionary]]<ref name="OED" />
* {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|s}} {{respell|BEE|təl|jooss}}{{snd}}[[Canadian Oxford Dictionary]] and ''Webster's Collegiate Dictionary''<ref name="MWD" /><!-- Schaaf says all 3 pronunciations used -->

=== Etymology ===
[[File:Al-Sufi's Orion, 1125 Baghdad copy, Doha Museum of Islamic Art Ms 2. 1998. SO.jpg|thumb|An illustration of Orion (horizontally reversed) in [[Abd al-Rahman al-Sufi|al-Sufi]]'s ''[[Book of Fixed Stars]]''. Betelgeuze is annotated as ''Yad al-Jauzā'' ("Hand of Orion"), one of the proposed etymological origins of its modern name, and also as ''Mankib al Jauzā''' ("Shoulder of Orion").]]

Betelgeuse is often mistranslated as "armpit of the central one".<ref>{{cite book | first=Ian | last=Ridpath | year=2006 | author-link=Ian Ridpath | page=8 | title=The Monthly Sky Guide | edition=7th | publisher=Cambridge University Press | isbn=978-0-521-68435-4 | url=https://books.google.com/books?id=P3JhtnAX-PwC&pg=PA8 }}</ref> In his 1899 work ''[[Star Names|Star-Names and Their Meanings]]'', American amateur naturalist Richard Hinckley Allen stated the derivation was from the {{nowrap|{{lang|ar|ابط الجوزاء}}}} ''{{transliteration|ar|Ibṭ al-Jauzah}}'', which he claimed degenerated into a number of forms, including ''Bed Elgueze'', ''Beit Algueze'', ''Bet El-gueze'', and ''Beteigeuze'', to the forms ''Betelgeuse'', ''Betelguese'', ''Betelgueze'' and ''Betelgeux''. The star was named ''Beldengeuze'' in the ''[[Alfonsine tables|Alfonsine Tables]]'',<ref name="Kunitzsch86">{{cite journal|last=Kunitzsch|first=Paul|year=1986|title=The Star Catalogue Commonly Appended to the Alfonsine Tables|journal=Journal for the History of Astronomy|volume=17|issue=49|pages=89–98|bibcode = 1986JHA....17...89K |doi=10.1177/002182868601700202|s2cid=118597258}}</ref> and Italian [[Jesuit]] priest and astronomer [[Giovanni Battista Riccioli]] had called it ''Bectelgeuze'' or ''Bedalgeuze''.<ref name="allen">{{cite book | author-link=Richard Hinckley Allen | author=Allen, Richard Hinckley | year=1963 | orig-year=1899 | title=Star Names: Their Lore and Meaning | edition=[[Reprint|rep]]. | publisher=[[Dover Publications]] Inc. | location=New York, [[New York (state)|NY]] | url=https://archive.org/details/starnamestheirlo00alle/page/310 | isbn=((978-0-486-21079-7)) | pages=[https://archive.org/details/starnamestheirlo00alle/page/310 310–12] }}</ref>

Paul Kunitzsch, Professor of Arabic Studies at the University of Munich, refuted Allen's derivation and instead proposed that the full name is a corruption of the Arabic {{lang|ar|يد الجوزاء}} ''{{transliteration|ar|Yad al-Jauzā'}}'', meaning "the Hand of ''al-Jauzā<nowiki>'"</nowiki>''; ''i.e.'', Orion.<ref name="KUNITZSCH1959">{{cite book |author=Kunitzsch, Paul |year=1959 |title=Arabische Sternnamen in Europa |publisher=[[Otto Harrassowitz]] |location=Wiesbaden |bibcode=1959ase..book.....K }}</ref> European mistransliteration into [[medieval Latin]] led to the first character ''y'' ('''ﻴ''', with two dots underneath) being misread as a ''b'' ('''ﺒ''', with only one dot underneath). During the [[Renaissance]], the star's name was written as {{lang|ar|بيت الجوزاء}} ''{{transliteration|ar|Bait al-Jauzā'}}'' ("house of Orion") or {{lang|ar|بط الجوزاء}} ''{{transliteration|ar|Baţ al-Jauzā'}}'', incorrectly thought to mean "armpit of Orion" (a true translation of "armpit" would be {{lang|ar|ابط}}, transliterated as ''{{transliteration|ar|Ibţ}})''. This led to the modern rendering as ''Betelgeuse''.<ref name="Kunitzsch">{{cite book |last1=Kunitzsch|first1=Paul |last2=Smart|first2= Tim |year = 2006 |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations |edition = 2nd rev. |publisher = [[Sky Publishing Corporation]] |location = [[Cambridge, Massachusetts|Cambridge]], [[Massachusetts|MA]] |isbn = 978-1-931559-44-7 |page = 45}}</ref> Other writers have since accepted Kunitzsch's explanation.<ref name="100greatest"/>

The last part of the name, "-elgeuse", comes from the Arabic {{lang|ar|الجوزاء}} ''{{transliteration|ar|al-Jauzā'}}'', a historical Arabic name of the constellation [[Orion (constellation)|Orion]], a feminine name in old [[Arabian legend]], and of uncertain meaning. Because {{lang|ar|جوز}} ''{{transliteration|ar|j-w-z}}'', the [[Root (linguistics)|root]] of ''{{transliteration|ar|jauzā'}}'', means "middle", ''{{transliteration|ar|al-Jauzā'}}'' roughly means "the Central One". The modern Arabic name for Orion is {{lang|ar|الجبار}} ''{{transliteration|ar|al-Jabbār}}'' ("the Giant"), although the use of {{lang|ar|الجوزاء}} ''{{transliteration|ar|al-Jauzā'}}'' in the star's name has continued.<ref name="Kunitzsch" /> The 17th-century English translator [[Edmund Chilmead]] gave it the name ''Ied Algeuze'' ("Orion's Hand"), from [[Jakob Christmann|Christmannus]].<ref name="allen" /> Other Arabic names recorded include {{lang|ar| اليد اليمنى}} ''{{transliteration|ar|Al Yad al Yamnā}}'' ("the Right Hand"), {{lang|ar|الذراع}} ''{{transliteration|ar|Al Dhira}}'' ("the Arm"), and {{lang|ar|المنكب}} ''{{transliteration|ar|Al Mankib}}'' ("the Shoulder"), all of al-Jauzā, Orion,<ref name="allen" /> as {{lang|ar|منكب الجوزاء}} ''{{transliteration|ar|Mankib al Jauzā'}}''.
[[File:Dunhuang Star Atlas - Orion.jpg|thumb|right|[[Dunhuang Star Chart]], ''circa'' AD 700, showing {{lang|zh|參宿四}} {{lang|zh-Latn|Shēnxiùsì}} (Betelgeuse), the Fourth Star of the constellation of Three Stars]]

=== Other names ===
Other names for Betelgeuse included the Persian ''{{lang|fa-Latn|Bašn}}'' "the Arm", and [[Coptic language|Coptic]] ''{{lang|cop-Latn|Klaria}}'' "an Armlet".<ref name="allen" /> ''{{lang|sa-Latn|Bahu}}'' was its [[Sanskrit]] name, as part of a Hindu understanding of the constellation as a running antelope or stag.<ref name="allen" /> In traditional [[Chinese astronomy]], the [[Chinese star names|name]] for Betelgeuse is {{lang|zh|参宿四}} (''{{lang|zh-Latn|Shēnxiùsì}}, the Fourth Star of the constellation of [[Three Stars (Chinese constellation)|Three Stars]]'')<ref name="sb2">{{Cite web |url=http://aeea.nmns.edu.tw/2006/0605/ap060525.html |publisher=AEEA (Activities of Exhibition and Education in Astronomy) |title=天文教育資訊網 2006 年 5 月 25 日 |trans-title=Astronomy Education Information Network 25 May 2006 |website=aeea.nmns.edu.tw |date=25 May 2006 |access-date=26 June 2012 |archive-date=16 July 2011 |archive-url=https://web.archive.org/web/20110716122642/http://aeea.nmns.edu.tw/2006/0605/ap060525.html |url-status=dead }}</ref> as the [[Orion in Chinese astronomy|Chinese constellation]] {{lang|zh|参宿}} originally referred to the three stars in [[Orion's Belt]]. This constellation was ultimately expanded to ten stars, but the earlier name stuck.<ref name="ridpath">{{cite web |url = http://www.ianridpath.com/startales/orion2.html#chinese |last = Ridpath |first = Ian |title = Orion: Chinese associations |access-date =24 June 2012 |work = Star Tales}}</ref> In Japan, the [[Heike clan|Taira, or Heike, clan]] adopted Betelgeuse and its red color as its symbol, calling the star ''Heike-boshi'', ({{lang|ja|平家星}}), while the [[Minamoto clan|Minamoto, or Genji, clan]] chose Rigel and its white color. The two powerful families fought a [[Genpei War|legendary war]] in Japanese history, the stars seen as facing each other off and only kept apart by the Belt.<ref name="RENSHAW1">{{cite web
 |title=''Yowatashi Boshi''; Stars that Pass in the Night
 |author1=Steve Renshaw
 |author2=Saori Ihara
 |name-list-style=amp
 |url=http://www.renshaworks.com/jastro/orion.htm
 |access-date=25 June 2012
 |archive-url=https://web.archive.org/web/20160604221737/http://www.renshaworks.com/jastro/orion.htm
 |archive-date=2016-06-04
 |url-status=usurped
}} Other Versions: {{cite magazine
 |title=''Yowatashi Boshi''; Stars that Pass in the Night
 |magazine=Griffith Observer
 |date=October 1999 | volume=63|issue=10|pages=2–17
}} and {{cite magazine
 |title=''Yowatashi Boshi''; Stars that Pass in the Night
 |magazine=The Kyoto Journal |issue=48 |date=July 2000
}}</ref><ref>[[Hōei Nojiri]]"Shin seiza jyunrei"p.19 {{ISBN|978-4-12-204128-8}}</ref>

In Tahitian lore, Betelgeuse was one of the pillars propping up the sky, known as ''Anâ-varu'', the pillar to sit by. It was also called ''Ta'urua-nui-o-Mere'' "Great festivity in parental yearnings".<ref name="henry1907">{{cite journal|last=Henry|first=Teuira |author-link=Teuira Henry |year=1907|title=Tahitian Astronomy: Birth of Heavenly Bodies|journal=The Journal of the Polynesian Society |volume=16|issue=2|pages=101–04|jstor=20700813}}</ref> A Hawaiian term for it was ''Kaulua-koko'' ("brilliant red star").<ref name="brosch">{{Cite book | last=Brosch | first=Noah | title=Sirius Matters | year=2008 | publisher=Springer | isbn=978-1-4020-8318-1 | page= 46 |url = https://books.google.com/books?id=ricStR4SE-UC&pg=PA46}}</ref> The [[Lacandon people]] of Central America knew it as ''chäk tulix'' ("red butterfly").<ref>{{cite book|last=Milbrath|first=Susan|title=Star Gods of the Maya: Astronomy in Art, Folklore, and Calendars|publisher=University of Texas Press|location=Austin, Texas|year=1999|page=39|isbn=978-0-292-75226-9|url=https://books.google.com/books?id=iZN6AAAAMAAJ}}</ref>

Astronomy writer [[Robert Burnham Jr.]] proposed the term ''padparadaschah'', which denotes a rare orange sapphire in India, for the star.<ref name="schaaf" />

=== Mythology ===
With the [[history of astronomy]] intimately associated with mythology and astrology before the [[scientific revolution]], the red star, like the planet Mars that derives its name from a [[Mars (mythology)|Roman war god]], has been closely associated with the martial [[archetype]] of conquest for millennia, and by extension, the motif of death and rebirth.<ref name="allen" /> Other cultures have produced different myths. Stephen R. Wilk has proposed the constellation of Orion could have represented the Greek mythological figure [[Pelops]], who had an artificial shoulder of ivory made for him, with Betelgeuse as the shoulder, its color reminiscent of the reddish yellow sheen of ivory.<ref name="wilk99" />

[[Australian Aborigines|Aboriginal]] people from the [[Great Victoria Desert]] of South Australia incorporated Betelgeuse into their oral traditions as the club of Nyeeruna (Orion), which fills with fire-magic and dissipates before returning. This has been interpreted as showing that early Aboriginal observers were aware of the brightness variations of Betelgeuse.<ref>{{cite journal|last1=Hamacher|first1=D.W.|title=Observations of red–giant variable stars by Aboriginal Australians|journal=The Australian Journal of Anthropology|volume=29|pages=89–107|doi=10.1111/taja.12257|arxiv=1709.04634|bibcode=2018AuJAn..29...89H|year=2018|s2cid=119453488}}</ref><ref>{{cite journal|last1=Leaman|first1=T.|last2=Hamacher|first2=D.W.|title=Aboriginal Astronomical traditions from Ooldea, South Australia, Part 1: Nyeeruna and the Orion Story|journal=Journal of Astronomical History and Heritage|date=2014|volume=17|issue=2|pages=180–194|doi=10.3724/SP.J.1440-2807.2014.02.05 |arxiv=1403.7849|bibcode=2014JAHH...17..180L|s2cid=53477850 }}</ref> The [[Wardaman people]] of northern Australia knew the star as ''Ya-jungin'' ("Owl Eyes Flicking"), its variable light signifying its intermittent watching of ceremonies led by the Red Kangaroo Leader Rigel.<ref>{{cite book|last1=Harney |first1=Bill Yidumduma |last2=Cairns |first2=Hugh C. |title=Dark Sparklers |publisher=Hugh C. Cairns |location=Merimbula, New South Wales |pages=139–40 |year=2004 |orig-year=2003 |edition=Revised |isbn=978-0-9750908-0-0}}</ref> In South African mythology, Betelgeuse was perceived as a lion casting a predatory gaze toward the three zebras represented by Orion's Belt.<ref>{{cite book|first=C. Scott |last=Littleton |year=2005 |page=1056 |title=Gods, goddesses, and mythology | volume=1 |publisher=Marshall Cavendish |isbn=978-0-7614-7559-0 |url=https://books.google.com/books?id=HC93q4gsOAwC&pg=PA1056 }}</ref>

In the Americas, Betelgeuse signifies a severed limb of a man-figure (Orion)—the [[Pemon people|Taulipang]] of Brazil know the constellation as Zililkawai, a hero whose leg was cut off by his wife, with the variable light of Betelgeuse linked to the severing of the limb. Similarly, the [[Lakota people]] of North America see it as a chief whose arm has been severed.<ref name="wilk99">{{cite journal|last=Wilk|first=Stephen R.|year=1999|title=Further Mythological Evidence for Ancient Knowledge of Variable Stars|journal= The Journal of the American Association of Variable Star Observers|volume=27|issue=2|pages=171–74|bibcode=1999JAVSO..27..171W}}</ref>

A Sanskrit name for Betelgeuse is ārdrā ("the moist one"), eponymous of the [[Ardra Nakshatra|Ardra]] [[nakshatra|lunar mansion]] in [[Hindu astrology]].<ref name="motz">{{cite book|last=Motz|first=Lloyd|author2=Nathanson, Carol|title=The Constellations: An Enthusiast's Guide to the Night Sky|publisher=Aurum Press|location=London, United Kingdom|year=1991|page=85|isbn=978-1-85410-088-7}}</ref> The [[Rigvedic deities|Rigvedic God]] of storms [[Rudra]] presided over the star; this association was linked by 19th-century star enthusiast [[Star Names: Their Lore and Meaning|Richard Hinckley Allen]] to Orion's stormy nature.<ref name="allen" /> The constellations in Macedonian folklore represented agricultural items and animals, reflecting their way of life. To them, Betelgeuse was ''Orach'' ("the ploughman"), alongside the rest of Orion, which depicted a plough with oxen. The rising of Betelgeuse at around 3&nbsp;a.m. in late summer and autumn signified the time for village men to go to the fields and plough.<ref>{{cite journal|title=Macedonian Folk Constellations |author=Cenev, Gjore |journal=Publications of the Astronomical Observatory of Belgrade|volume= 85|pages=97–109|bibcode=2008POBeo..85...97C|year=2008}}</ref> To the [[Inuit astronomy|Inuit]], the appearance of Betelgeuse and [[Bellatrix]] high in the southern sky after sunset marked the beginning of spring and lengthening days in late February and early March. The two stars were known as ''Akuttujuuk'' ("those [two] placed far apart"), referring to the distance between them, mainly to people from North Baffin Island and Melville Peninsula.<ref name=inuit/>

The opposed locations of Orion and [[Scorpius]], with their corresponding bright red variable stars Betelgeuse and [[Antares]], were noted by ancient cultures around the world. The setting of Orion and rising of Scorpius signify the death of Orion by the scorpion. In China they signify brothers and rivals Shen and Shang.<ref name="wilk99" /> The [[Batak (Indonesia)|Batak]] of Sumatra marked their New Year with the first [[new moon]] after the sinking of Orion's Belt below the horizon, at which point Betelgeuse remained "like the tail of a rooster". The positions of Betelgeuse and Antares at opposite ends of the celestial sky were considered significant, and their constellations were seen as a pair of scorpions. Scorpion days marked as nights that both constellations could be seen.<ref name="kelley11">{{cite book|author1=Kelley, David H. |author2=Milone, Eugene F. |author3=Aveni, A.F. |title=Exploring Ancient Skies: A Survey of Ancient and Cultural Astronomy|publisher=Springer|location=New York, New York|year=2011|page=307|isbn=978-1-4419-7623-9|url=https://books.google.com/books?id=ILBuYcGASxcC&pg=PA307}}</ref>

=== In popular culture ===
As one of the brightest and best-known stars, Betelgeuse has featured in many works of fiction. The star's unusual name inspired the title of the 1988 film ''[[Beetlejuice]]'', referring to its titular antagonist, and script writer [[Michael McDowell (author)|Michael McDowell]] was impressed by how many people made the connection.<ref name="schaaf" /><!-- ref cites two previous sentences --> In the popular science fiction series ''[[The Hitchhiker's Guide to the Galaxy]]'' by [[Douglas Adams]], [[Ford Prefect (character)|Ford Prefect]] was from "a small planet somewhere in the vicinity of Betelgeuse."<ref name="conley">{{cite book
 |title=Magic Words: A Dictionary
 |author=Conley, Craig
 |year=2008
 |page=121
 |url=https://books.google.com/books?id=3SB60Wavy6MC&pg=PA121
 |access-date=22 September 2010
 |isbn=978-1-57863-434-7
 |publisher=Weiser}}</ref>

Two American navy ships were named after the star, both of them World War II vessels, the {{USS|Betelgeuse|AKA-11}} launched in 1939 and {{USS|Betelgeuse|AK-260}} launched in 1944. In 1979, the French supertanker ''[[Whiddy Island disaster|Betelgeuse]]'' was moored off [[Whiddy Island]], discharging oil when it exploded, killing 50 people in one of the worst disasters in Ireland's history.<ref>{{cite news
 | first=Nicolla | last=Tallant | date=15 July 2007
 | work=Independent Digital
 | publisher=Independent News & Media PLC
 | title=Survivor recalls the night an apocalypse came to Whiddy
 | url=http://www.independent.ie/national-news/survivor-recalls-the-night-an-apocalypse-came-to-whiddy-1037842.html
 | access-date=10 June 2011}}</ref>

The [[Dave Matthews Band]] song "[[Black and Blue Bird (song)|Black and Blue Bird]]" references the star.<ref>{{cite web|url=http://dmbalmanac.com/Lyrics.aspx?iid=55845&sid=2828 |title=Black and Blue Bird |website=Dmbalmanac.com |date=5 July 2015 |access-date=30 January 2016}}</ref> The [[Blur (band)|Blur]] song "Far Out" from their 1994 album [[Parklife]] mentions Betelgeuse in its lyrics.<ref>{{cite web |title=Blur – Far Out Lyrics |url=https://genius.com/Blur-far-out-lyrics |website=genius.com |access-date=7 February 2020}}</ref>

The [[Philip Larkin]] poem "The North Ship", found in [[The North Ship|the collection of the same name]], references the star in the section "Above 80° N", which reads:
<blockquote>"&thinsp;'A woman has ten claws,' <br/>
Sang the drunken boatswain; <br/>
Farther than Betelgeuse,  <br/>
More brilliant than Orion  <br/>
Or the planets Venus and Mars, <br/>
The star flames on the ocean;  <br/>
'A woman has ten claws,' <br/>
Sang the drunken boatswain."</blockquote>
[[Humbert Wolfe]] wrote a poem about Betelgeuse, which was set to music by [[Gustav Holst]].<ref>{{cite book | chapter-url=https://books.google.com/books?id=4L0gidyMKgEC | title=Try Whistling This: Writings on Music | publisher=Black Incorporated | author-link=Andrew Ford (composer) | year=2012 | location=Collingwood, Victoria | isbn=9781921870682 | last=Ford | first=Andrew | chapter=Holst, the Mystic}}</ref>

== Table of angular diameter estimates ==
This table provides a non-exhaustive list of angular measurements conducted since 1920. 
{| class="wikitable" style="text-align:center;"
! style="width:50pt; text-align:left;"|Article
! style="width:30pt;"|Year{{efn|The final year of observations, unless otherwise noted}}
! style="width:50pt;"|Telescope
! style="width:15pt;"|[[Measurements|#]]
! style="width:82pt;"|[[Electromagnetic spectrum|Spectrum]]
! style="width:70pt;"|<big>{{mvar|λ}}</big> ([[Micrometre|μm]])
! style="width:75pt;"|<big>∅</big> ([[Milliarcseconds|mas]]){{efn|Uniform disk measurement, unless otherwise noted}}
! Notes
|-
|style="text-align:left;"|[[Albert A. Michelson|Michelson]]<ref name="MICHELSON" />
|1920
|[[Mount Wilson Observatory|Mount Wilson]]
|1
|[[Visible spectrum|Visible]]
|0.575
|{{val|47.0|4.7}}
|style="text-align:left;"|Limb darkened +17% = 55.0
|-
|style="text-align:left;"|Bonneau<ref name="BONNEAU1973"/>
|1972
|[[Palomar Observatory|Palomar]]
|8
|Visible
|0.422–0.719
|52.0–69.0
|style="text-align:left;"|Strong correlation of <big>∅</big> with <big>{{mvar|λ}}</big>
|-
|style="text-align:left;" rowspan="2"|Balega<ref name=BALEGA/>
|1978
|style="text-align:center;"|[[ESO 3.6 m Telescope|ESO]]
|3
|Visible
|0.405–0.715
|45.0–67.0
|rowspan="2" style="text-align:left;"|No correlation of <big>∅</big> with <big>{{mvar|λ}}</big>
|-
|1979
|[[Special Astrophysical Observatory of the Russian Academy of Science|SAO]]
|4
|Visible
|0.575–0.773
|50.0–62.0
|-
|style="text-align:left;"|Buscher<ref name="BUSCHER" />
|1989
|[[William Herschel Telescope|WHT]]
|4
|Visible
|0.633–0.710
|54.0–61.0
|style="text-align:left;"|Discovered asymmetries/hotspots
|-
|style="text-align:left;"|Wilson<ref name="WILSON2" />
|1991
|WHT
|4
|Visible
|0.546–0.710
|49.0–57.0
|style="text-align:left;"|Confirmation of hotspots
|-
|style="text-align:left;" rowspan="2"|Tuthill<ref name="TUTHILL" />
|1993
|WHT
|8
|Visible
|0.633–0.710
|43.5–54.2
|rowspan="2" style="text-align:left;"|Study of hotspots on 3 stars
|-
|1992
|WHT
|1
|[[Infrared#Astronomy division scheme|NIR]]
|0.902
|{{val|42.6|3.0}}
|-
|rowspan="2" style="text-align:left;"|Gilliland<ref name="GILLILAND1" />
|rowspan="2"|1995
|rowspan="2"|[[Hubble Space Telescope|HST]]
|rowspan="2"|
|rowspan="2"|[[ultraviolet|UV]]
|0.24–0.27
|104–112
|rowspan="2" style="text-align:left;"|FWHM diameters
|-
|0.265–0.295
|92–100
|-
|style="text-align:left;"|Weiner<ref name="WEINER" />
|1999
|[[Infrared Spatial Interferometer|ISI]]
|2
|MIR ([[Infrared astronomy#Modern infrared astronomy|N Band]])
|11.150
|{{val|54.7|0.3}}
|style="text-align:left;"|Limb darkened = {{val|55.2|0.5}}
|-
|style="text-align:left;"|Perrin<ref name="PERRIN2" />
|1997
|[[Infrared Optical Telescope Array|IOTA]]
|7
|NIR ([[K band (infrared)|K band]])
|2.200
|{{val|43.33|0.04}}
|style="text-align:left;"|[[K band (infrared)|K]] and [[L band (infrared)|L bands]], {{val|11.5|u=μm}} data contrast
|-
|style="text-align:left;"|Haubois<ref name="HAUBOIS" />
|2005
|IOTA
|6
|NIR ([[H band (infrared)|H band]])
|1.650
|{{val|44.28|0.15}}
|style="text-align:left;"|Rosseland diameter {{val|45.03|0.12}}
|-
|style="text-align:left;"|Hernandez<ref name="HERNANDEZ" />
|2006
|[[Very Large Telescope|VLTI]]
|2
|NIR (K band)
|2.099–2.198
|{{val|42.57|0.02}}
|style="text-align:left;"|High precision AMBER results.
|-
|style="text-align:left;"|Ohnaka<ref name="OHNAKA2009" />
|2008
|VLTI
|3
|NIR (K band)
|2.280–2.310
|{{val|43.19|0.03}}
|style="text-align:left;"|Limb darkened {{val|43.56|0.06}}
|-
|style="text-align:left;" rowspan="3"|Townes<ref name="TOWNES1" />
|1993
|ISI
|rowspan="3"|17
|[[Infrared#Astronomy division scheme|MIR]] (N band)
|11.150
|{{val|56.00|1.00}}
|style="text-align:left;" rowspan="3"|Systematic study involving 17 measurements at the same wavelength from 1993 to 2009
|-
|2008
|ISI
|MIR (N band)
|11.150
|{{val|47.00|2.00}}
|-
|2009
|ISI
|MIR (N band)
|11.150
|{{val|48.00|1.00}}
|-
|style="text-align:left;"|Ohnaka<ref name="OHNAKA2011" />
|2011
|VLTI
|3
|NIR (K band)
|2.280–2.310
|{{val|42.05|0.05}}
|style="text-align:left;"|Limb darkened {{val|42.49|0.06}}
|-
|style="text-align:left;"|Harper<ref name="HARPER" />
|2008
|[[Very Large Array|VLA]]
|
| colspan="4" style="text-align:left;" |Also noteworthy, Harper ''et al.'' in the conclusion of their paper make the following remark: ''"In a sense, the derived distance of {{val|200|u=pc}} is a balance between the {{val|131|u=pc}} ({{val|425|u=ly}}) Hipparcos distance and the radio which tends towards {{val|250|u=pc}} ({{val|815|u=ly}})"''—hence establishing ± {{val|815|u=ly}} as the outside distance for the star.
|}

== See also ==
* [[List of stars in Orion]]
* [[List of stars that have unusual dimming periods]]
* [[Stellar evolution]]
* [[List of semiregular variable stars]]
* [[List of supernova candidates]]

==Notes==
{{notelist}}

== References ==
{{reflist|25em}}

== External links ==
{{Commons category|Betelgeuse}}
{{Wiktionary|Betelgeuse}}
* [http://www.mrao.cam.ac.uk/outreach/radio-telescopes/coast/coast-astronomical-results/surface-imaging-of-betelgeuse/ Surface imaging of Betelgeuse with COAST and the WHT] – interferometric images taken at different wavelengths
* [http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/irregions.html Near, mid and far infrared] {{Webarchive|url=https://web.archive.org/web/20200429131359/http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/irregions.html |date=29 April 2020 }} – Infrared Processing and Analysis Center (IPAC) webpage showing pictures at various wavelengths
* [[Astronomy Picture of the Day|APOD]] Pictures:
# [http://apod.nasa.gov/apod/ap071225.html Mars and Orion over Monument Valley] skyscape showing the relative brightness of Betelgeuse and Rigel
# [http://apod.nasa.gov/apod/ap101023.html Orion: head to toe] breathtaking vista the Orion molecular cloud complex from Rogelio Bernal Andreo
# [http://apod.nasa.gov/apod/ap100106.html The spotty surface of Betelgeuse] – a reconstructed image showing two hotspots, possibly convection cells
# [http://apod.nasa.gov/apod/ap001222.html Simulated Supergiant Star] – Freytag's "Star in a Box" illustrating the nature of Betelgeuse's "monster granules"
# [http://apod.nasa.gov/apod/ap000725.html Why stars twinkle] – image of Betelgeuse showing the effect of atmospheric twinkling in a telescope
* [http://www.astro.uu.se/~bf/movie/dst35gm04n26/rsgintro_en.html Red supergiant movie] – numerical simulation of a red supergiant star like Betelgeuse

{{Stars of Orion}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Authority control}}
<!-- Properties -->

{{DEFAULTSORT:Betelgeuse}}
[[Category:M-type supergiants]]
[[Category:Semiregular variable stars]]
[[Category:Runaway stars]]
[[Category:Population I stars]]
<!-- Location/catalogues -->
[[Category:Orion (constellation)]]
[[Category:Bayer objects|Orionis, Alpha]]
[[Category:Bright Star Catalogue objects|2061]]
[[Category:Durchmusterung objects]]
[[Category:Flamsteed objects|Orionis, 58]]
[[Category:Henry Draper Catalogue objects|039801]]
[[Category:Hipparcos objects|027989]]
[[Category:TIC objects]]
[[Category:Stars with proper names]]