View source for Betelgeuse

{{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
  | x = 448 | y = 312
  }}
 | caption = Betelgeuse (circled) in the constellation Orion 
}}
{{Starbox observe
|epoch = J2000.0
|constell = [[Orion (constellation)|Orion]]
|pronounce = {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|z|,_|ˈ|b|ɛ|t|əl|-|,_|-|dʒ|uː|s}}<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>
|ra = {{RA|05|55|10.30536}}<ref name=hipparcos/>
|dec = {{DEC|+07|24|25.4304}}<ref name=hipparcos/>
}}
{{Starbox character
| type=[[Red supergiant]]
|class = M1–M2 Ia–ab<ref name=mk>{{cite journal|bibcode=1989ApJS...71..245K|title=The Perkins catalog of revised MK types for the cooler stars|journal=Astrophysical Journal Supplement Series|volume=71|pages=245|author1=Keenan|first1=Philip C.|last2=McNeil|first2=Raymond C.|year=1989|doi=10.1086/191373}}</ref>
| appmag_1_passband = [[Visible spectrum|V]]
| appmag_1 = 0.50<ref name="NICOLET" /> {{nowrap|(0.0 - 1.3<ref name=gcvs/>)}}
| appmag_2_passband = [[J band (infrared)|J]]
| appmag_2 = −3.00<ref name=ducati>{{cite journal|bibcode=2002yCat.2237....0D|title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system|journal=CDS/ADC Collection of Electronic Catalogues|volume=2237|author1=Ducati|first1=J. R.|year=2002}}</ref>
| appmag_3_passband = [[K band (infrared)|K]]
| appmag_3 = −4.05<ref name=ducati/>
|b-v = +1.85<ref name="NICOLET">{{cite journal
 | author=Nicolet, B.
 | title=Catalogue of Homogeneous Data in the UBV Photoelectric Photometric System
 | journal=Astronomy & Astrophysics
 | year=1978
 | volume=34
 | pages=1–49
 | bibcode=1978A&AS...34....1N
 | doi= }}</ref>
|u-b = +2.06<ref name="NICOLET" />
|variable = [[semiregular variable star|SRc]]<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S|volume=1|display-authors=etal|author1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
}}
{{Starbox astrometry
|radial_v = +21.91<ref>{{cite journal|bibcode=2005A&A...430..165F|title=Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data.  Revisiting the concept of superclusters|journal=Astronomy and Astrophysics|volume=430|pages=165|author1=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|doi=10.1051/0004-6361:20041272|arxiv = astro-ph/0409579 }}</ref>
|prop_mo_ra = {{nowrap|26.42 ± 0.25<ref name=harper2017/>}}
|prop_mo_dec = {{nowrap|9.60 ± 0.12<ref name=harper2017/>}}
|parallax = 4.51
|p_error = 0.80
|parallax_footnote=<ref name=harper2017/>
|dist_ly =
|dist_pc = {{val|222|48|34}}<ref name=harper2017/>
|absmag_v = −5.85<ref name=HARPER/>
}}
{{Starbox detail
|mass={{val|11.6|5.0|3.9}}<ref name="NEILSON2011"/>
|radius=887 ± 203<ref name=dolan2016 />, {{nowrap|{{val|955|217}}<ref name="NEILSON2011"/>}}
|luminosity={{val|90000}} – {{val|150000}}<ref name="SMITH2009"/>
|temperature={{val|3590}}<ref name="NEILSON2011"/>
|gravity=−0.5<ref name="LOBEL">{{cite journal
|author1=Lobel, Alex |author2=Dupree, Andrea K. | title=Modeling the Variable Chromosphere of α Orionis
| journal=The Astrophysical Journal
| year=2000
| volume=545
| issue=1
| pages=454–74
| url=http://iopscience.iop.org/0004-637X/545/1/454/pdf/51504.web.pdf
| accessdate=10 July 2010
| bibcode=2000ApJ...545..454L
| doi=10.1086/317784}}</ref>
| metal_fe=+0.05<ref name="RAMIREZ">{{cite journal
| author=Ramírez, Solange V.
| title=Stellar Iron Abundances at the Galactic Center
| journal=The Astrophysical Journal
| date=July 2000
| volume=537
| issue=1
| pages=205–20
| url=http://iopscience.iop.org/0004-637X/537/1/205/pdf/50790.web.pdf
| format=PDF
| accessdate=9 July 2010
| bibcode=2000ApJ...537..205R
| doi=10.1086/309022|arxiv = astro-ph/0002062
| last2=Sellgren
| first2=K.
| last3=Carr
| first3=John S.
| last4=Balachandran
| first4=Suchitra C.
| display-authors=4
| last5=Blum
| first5=Robert
| last6=Terndrup
| first6=Donald M.
| last7=Steed
| first7=Adam}}</ref>
|rotational_velocity=5<ref name="KERVELLA2009" />
|age_myr = 8.0 – 8.5<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|pages=7|year=2016|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 }}</ref>
}}
{{Starbox catalog
|names=Betelgeuse, [[Bayer designation|α Ori]], [[Flamsteed designation|58&nbsp;Ori]], [[Harvard Revised catalogue|HR]]&nbsp;2061, [[Bonner Durchmusterung|BD]]+7°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+0724AP, [[American Association of Variable Star Observers|AAVSO]]&nbsp;0549+07
}}
{{Starbox reference
|Simbad=HD+39801}}
{{Starbox end}}
[[File:Betelgeuse captured by ALMA.jpg|thumb|This orange blob shows the nearby star Betelgeuse, as seen by the Atacama Large Millimeter/submillimeter Array (ALMA). This is the first time that ALMA has ever observed the surface of a star and this first attempt has resulted in the highest-resolution image of Betelgeuse available.]]
'''Betelgeuse''', also designated '''Alpha Orionis''' ('''α Orionis''', abbreviated '''Alpha Ori''', '''α Ori'''), is the 9th brightest [[star]] in the night sky and second-brightest in the Orion constellation. It is distinctly reddish, and is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first magnitude star. Betelgeuse is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon. It would be the brightest star in the night sky if the human eye could view all wavelengths of radiation.

Classified as a with a [[stellar classification|spectral type]] M1-2, the star is one of the [[List:Largest known stars|largest]] and most luminous stars visible to the naked eye. If Betelgeuse were at the center of the [[Solar System]], its surface would extend past the orbit of [[Jupiter]]. Having been ejected from its birthplace in the Orion OB1 Association, which includes the stars in Orion's Belt, this runaway star has been observed moving through the interstellar medium at a speed of 30&nbsp;km/s, creating a bow shock over four light-years wide. Currently in a late stage of stellar evolution, the supergiant is expected to explode as a supernova within the next 10 to 1,000 years. The angular diameter of Betelgeuse is only exceeded by [[R Doradus]], not including the [[Sun]].

== Diameter ==
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 not yet widely developed, the experiment proved successful. The researchers used a uniform disk model to determine that Betelgeuse had a diameter of 0.047&nbsp;arcseconds, although the stellar disk was likely up to 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
 |author1=Townes, C. H. |author2=Wishnow, E. H. |author3=Hale, D. D. S. |author4=Walp, B. | journal=The Astrophysical Journal Letters
 | volume= 697
 | issue= 2
 | pages= L127–28
 | year=2009
 | url=http://iopscience.iop.org/1538-4357/697/2/L127/pdf/apjl_697_2_127.pdf
 | bibcode=2009ApJ...697L.127T
 | doi=10.1088/0004-637X/697/2/L127}}</ref> Since then, other studies have produced angular diameters that range from 0.042 to 0.069&nbsp;arcseconds.<ref name="BONNEAU1973"/><ref name="WEINER" /><ref name="BALEGA">{{cite journal
 | author=Balega, Iu. |author2=Blazit, A. |author3=Bonneau, D. |author4=Koechlin, L. |author5=Labeyrie, A. |author6=Foy, 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 815&nbsp;ly yields a projected radius of the stellar disk of anywhere from 1.2 to 8.9&nbsp;astronomical units.<ref name="NOTEANGULAR" group="note" /> Using the Solar System for comparison, the orbit of [[Solar System#Mars|Mars]] is about 1.5&nbsp;AU, [[Solar System#Ceres|Ceres]] in the [[asteroid belt]] 2.7&nbsp;AU, [[Solar System#Jupiter|Jupiter]] 5.5&nbsp;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 9.5&nbsp;AU.
[[File:Betelgeuse radio wavelengths.jpg|thumb|right|upright=1.2|Radio image from 1998 (pre-Harper) showing the size of Betelgeuse's photosphere (circle) and the effect of convective forces on the star's atmosphere]]

Betelgeuse's 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 | title=Interferometric Observations of the Supergiant Stars α Orionis and α Herculis with FLUOR at IOTA  |author1=Perrin, G. |author2=Ridgway, S. T. |author3=Coudé du Foresto, V. |author4=Mennesson, B. |author5=Traub, W. A. |author6=Lacasse, M. G. | journal=Astronomy and Astrophysics
 | volume=418
 | issue= 2
 | pages=675–85
 | year=2004
 | doi=10.1051/0004-6361:20040052
 | bibcode=2004A&A...418..675P
 | quote=Assuming a distance of 197 ± 45 pc, an angular distance of 43.33 ± 0.04 mas would equate to a radius of 4.3&nbsp;AU or {{solar radius|920}}|arxiv = astro-ph/0402099 }}</ref><ref name="YOUNG">{{cite web
 | last=Young
 | first=John
 | date=24 November 2006
 | url=http://www.mrao.cam.ac.uk/telescopes/coast/betel.html
 | 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]]
 | accessdate=21 June 2007
 | deadurl=yes
 | archiveurl=https://web.archive.org/web/20070614111315/http://www.mrao.cam.ac.uk/telescopes/coast/betel.html
 | archivedate=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" />
Which part of the electromagnetic spectrum—the visible, near-infrared ([[Infrared#Astronomy division scheme|NIR]]) or mid-infrared (MIR)—produces the most accurate angular measurement is still debated.<ref name="NOTEANGULAR" group="note" /> In 1996, Betelgeuse was shown to have a uniform disk of 56.6 ± 1.0&nbsp;mas. In 2000, the SSL team produced another measure of 54.7 ± 0.3&nbsp;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 55.2 ± 0.5&nbsp;mas. The earlier estimate equates to a radius of roughly 5.6&nbsp;AU or {{val|1200|u=R_solar}}, assuming the 2008 Harper distance of 197.0 ± 45&nbsp;pc,<ref name="SMITH2009">{{cite journal
 |author1=Smith, Nathan |author2=Hinkle, Kenneth H. |author3=Ryde, Nils | title=Red Supergiants as Potential Type IIn Supernova Progenitors: Spatially Resolved 4.6 μm CO Emission Around VY CMa and Betelgeuse
 | journal=The Astronomical Journal
 |date=March 2009
 | volume=137
 | issue=3
 | pages=3558–3573
 | arxiv=0811.3037
 | doi=10.1088/0004-6256/137/3/3558
 | bibcode=2009AJ....137.3558S}}</ref> a figure larger than the orbit of [[Saturn]]. A team of astronomers working in the near-infrared announced in 2004, that the more accurate photospheric measurement was 43.33 ± 0.04&nbsp;mas.<ref name="PERRIN2" /> 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 Perrin's analysis and yielded diameters ranging from 42.57 to 44.28&nbsp;mas with comparatively insignificant margins of error.<ref name="HAUBOIS">{{cite journal | author=Haubois, X.
 | title=Imaging the Spotty Surface of Betelgeuse in the H Band
 | journal=Astronomy & Astrophysics
 | year=2009
 | volume=508
 | issue=2
 | pages=923–32
 | bibcode=2009A&A...508..923H
 | doi=10.1051/0004-6361/200912927
 | last2=Perrin
 | first2=G.
 | last3=Lacour
 | first3=S.
 | last4=Verhoelst
 | first4=T.
 | last5=Meimon
 | first5=S.
 | display-authors=5
 | last6=Mugnier
 | first6=L.
 | last7=Thiébaut
 | first7=E.
 | last8=Berger
 | first8=J. P.
 | last9=Ridgway
 | first9=S. T.|arxiv = 0910.4167 }}</ref><ref name="HERNANDEZ">{{cite journal
 | author=Hernandez Utrera, O. |author2=Chelli, 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
}}</ref> In 2011, a third estimate in the near-infrared corroborating the 2009 numbers, this time showing a limb-darkened disk diameter of 42.49&nbsp;±&nbsp;0.06 mas.<ref name="OHNAKA2011">{{cite journal  |author1=Ohnaka, K. |author2=Weigelt, G. |author3=Millour, F. |author4=Hofmann, K.-H. |author5=Driebe, T. |author6=Schertl, D. |author7=Chelli, A. |author8=Massi, F. |author9=Petrov, R. |author10=Stee, Ph. | title=Imaging the Dynamical Atmosphere of the Red Supergiant Betelgeuse in the CO First Overtone Lines with VLTI/AMBER
 | journal=Astronomy & Astrophysics
 |date=May 2011
 | volume=529, id.A163
 | arxiv=1104.0958
 | doi=10.1051/0004-6361/201016279
 | bibcode=2011A&A...529A.163O
 | quote="We derive a uniform-disk diameter of 42.05 ± 0.05&nbsp;mas and a power-law-type limb-darkened disk diameter of 42.49 ± 0.06&nbsp;mas and a limb-darkening parameter of (9.7 ± 0.5) × 10<sup>−2</sup>"
 | pages=A163}}</ref> Consequently, if one combines the smaller Hipparcos distance from van Leeuwen of 152 ± 20&nbsp;pc with Perrin's angular measurement of 43.33&nbsp;mas, a near-infrared photospheric estimate would equate to about 3.4&nbsp;AU or {{solar radius|730}}.<ref name="KERVELLA2011">{{cite journal |author1=Kervella, P. |author2=Perrin, G. |author3=Chiavassa, A. |author4=Ridgway, S. T. |author5=Cami, J. |author6=Haubois, X. |author7=Verhoelst, T. | title=The Close Circumstellar Environment of Betelgeuse. II. Diffraction-limited Spectro-imaging from 7.76 to 19.50 μm with VLT/VISIR
 | journal=Astronomy & Astrophysics
 | year=2011
 | volume=531, id.A117
 | arxiv=1106.5041
 | doi=10.1051/0004-6361/201116962
 | bibcode=2011A&A...531A.117K
 | pages=A117}}</ref> Central to this discussion, it was announced in 2009, that the radius of Betelgeuse had shrunk from 1993 to 2009 by 15%, with the 2008 angular measurement equal to 47.0&nbsp;mas, not too far from Perrin's estimate.<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=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 1 Astrophysical Journal Letters.}}</ref> Unlike most earlier papers, this study encompassed a 15-year period at one specific wavelength. Earlier studies have typically lasted one to two years by comparison and have explored multiple wavelengths, often yielding vastly different results. The diminution in Betelgeuse's [[apparent size]] equates to a range of values between 56.0&nbsp;±&nbsp;0.1&nbsp;mas seen in 1993 to 47.0&nbsp;±&nbsp;0.1&nbsp;mas seen in 2008—a contraction of almost 0.9&nbsp;AU in 15&nbsp;years. What is not fully known is whether this observation is evidence of a rhythmic expansion and contraction of the star's photosphere as astronomers have theorized, and if so, what the periodic cycle might be, although Townes suggested that if a cycle does exist, it is probably a few decades long.<ref name="TOWNES1" /> Other possible explanations are photospheric protrusions due to convection or a star that is not spherical but asymmetric causing the appearance of expansion and contraction as the star rotates on its axis.<ref name="COURTLAND">{{cite web
 | author=Courtland, Rachel
 | year=2009
 | url=https://www.newscientist.com/article/dn17282-betelgeuse-the-incredible-shrinking-star.html
 | title=Betelgeuse: The incredible Shrinking Star?
 | work=New Scientist
 | publisher=Reed Business Information Ltd.
 |accessdate=25 September 2010}}</ref>

The debate about the vast differences between measurements in the mid-infrared, which suggest a possible expansion and contraction of the star, and the near-infrared, which advocates a relatively constant photospheric diameter, which remains to be resolved. But in a paper published in 2012, the Berkeley team reported that their measurements were "dominated by the behavior of cool, optically thick material above the stellar photosphere," indicating that the apparent expansion and contraction may be due to activity in the star's outer shells and not the photosphere itself.<ref name="RAVI1" /> This conclusion, if further corroborated, would suggest an average angular diameter for Betelgeuse closer to Perrin's estimate at 43.33&nbsp;arcseconds, hence a stellar radius of about 3.4&nbsp;AU ({{solar radius|730}}) assuming the shorter Hipparcos distance of 498&nbsp;±&nbsp;73&nbsp;ly in lieu of Harper's estimate at 643&nbsp;±&nbsp;146&nbsp;ly. The [[Gaia (spacecraft)|Gaia spacecraft]] may clarify assumptions presently used in calculating the size of Betelgeuse's stellar disk.

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

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, but there are widely used conversion factors depending on the wavelength used for the angular measurements.<ref name=dyck>{{cite journal|doi=10.1086/300453|title=Radii and Effective Temperatures for K and M Giants and Supergiants. II|journal=The Astronomical Journal|volume=116|issue=2|pages=981|year=1998|last1=Dyck|first1=H. M.|last2=Van Belle|first2=G. T.|last3=Thompson|first3=R. R.|bibcode=1998AJ....116..981D|citeseerx=10.1.1.24.1889}}</ref> For example, a measured angular diameter of 55.6 mas corresponds to a Rosseland mean diameter of 56.2 mas. The Rosseland radius derived from angular measurements of the star's photosphere rather than an extended envelope is {{solar radius|887}}.<ref name=dolan2016/>

==Evolution==
[[File:Hertzsprung-Russel StarData.png|thumb|right|upright=1.2|[[Hertzsprung–Russell diagram]] identifying supergiants like Betelgeuse that have moved off the [[main sequence]]]]
Betelgeuse is a red supergiant that has evolved from an O-type [[main sequence]] star, which was very similar to the other stars of [[Orion]]. Its core will eventually collapse, producing a [[supernova]] explosion and leaving behind a compact supernova remnant. The details depend on the exact initial mass and other physical properties of that main sequence star.
{{clear}}
== References ==
{{Reflist|30em}}
{{Portal|Astronomy|Star}}

{| border= "1"
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{{s-bef|before=[[Mu Cephei]]}}
{{s-ttl|title=[[List of largest known stars|Largest known star]]|years=2001}}{{cn|date=October 2017}}
1,180 {{solar radius}}
{{s-aft|after=[[VV Cephei]]}}
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{{Stars of Orion}}

{{featured article}}

[[Category:Arabic words and phrases]]
[[Category:Bayer objects|Orionis, Alpha]]
[[Category:Flamsteed objects|Orionis, 58]]
[[Category:Henry Draper Catalogue objects|039801]]
[[Category:Hipparcos objects|027989]]
[[Category:HR objects|2061]]
[[Category:M-type supergiants]]
[[Category:Orion (constellation)]]
[[Category:Semiregular variable stars]]
[[Category:Stars with proper names]]
[[Category:Durchmusterung objects]]