User:Sadalsuud/Beetle1geuse#Properties

Betelgeuse and its red coloration have been noted since antiquity; the classical astronomer Ptolemy described its color as ὑπόκιρρος (hypókirros), a term which was later described by a translator of Ulugh Beg's Zij-i Sultani as rubedo, Latin for "ruddiness".Stella lucida in umero dextro, quae ad rubedinem vergit. "Bright star in right shoulder, which inclines to ruddiness." In the nineteenth century, before modern systems of stellar classification, Angelo Secchi included Betelgeuse as one of the prototypes for his Class III (orange to red) stars.{{cite conference

| last=Brück | first=H. A. | year=1979

| title=P. Angelo Secchi, S. J. 1818–1878

| book-title=Spectral Classification of the Future, Proceedings of the IAU Colloq. 47

| location=Vatican City | date=11–15 July 1978

| editor=M. F. McCarthy, A. G. D. Philip, and G. V. Coyne

| pages=7–20 | bibcode=1979RA......9....7B }} By contrast, three centuries before Ptolemy, Chinese astronomers observed Betelgeuse as having a yellow coloration, suggesting that the star may have spent time as a yellow supergiant around the beginning of the common era,{{cite journal

| title=Ancient Chinese Suggest Betelgeuse is a Young Star

| page=238 | journal=New Scientist | date=22 October 1981

| volume=92 | issue=1276

| url=https://books.google.com/books?id=L4NTyHivbV8C&pg=PA238

| last1=Information

| first1=Reed Business }} an intriguing possibility given current research into the complex circumstellar environment of these stars.

File:Sir John Herschel with Cap, by Julia Margaret Cameron.jpg a few years before his death]]

The variation in Betelgeuse's brightness was first described in 1836 by Sir John Herschel, when he published his observations in Outlines of Astronomy. From 1836 to 1840 he noticed significant changes in magnitude with Betelgeuse outshining Rigel in October 1837 and again in November 1839. A quiescent period followed lasting about 10 years, then in 1849, Herschell noted another short cycle of variability which peaked in 1852. Later observers recorded unusually high maxima with an interval of several years, but only small variations from 1957 to 1967. The records of the American Association of Variable Star Observers (AAVSO) show a maximum brightness of 0.2 in the years 1933 and 1942, with a minimum of 1.2, observed in both 1927 and 1941.{{cite web

| title=Variable Star of the Month: Alpha Orionis

| publisher=American Association of Variable Star Observers (AAVSO)

| author=Davis, Kate (AAVSO Technical Assistant, Web)

| url=http://www.aavso.org/vsots_alphaori

| year=2000

| date=December 2000

| accessdate=10 July 2010}}{{cite book

| first=Robert

| last=Burnham

| authorlink=Robert Burnham, Jr.

| year=1978

| title=Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Volume 2

| page=1290

| publisher=Courier Dover Publications

| location=New York

| isbn=0-486-23568-8}} This variability in brightness may explain why Johann Bayer, with the publication of his Uranometria in 1603, designated the star alpha as it may have rivalled the usually brighter Rigel (beta).{{cite book

| title=The Hundred Greatest Stars

| author=Kaler, James B.

| year=2002

| publisher=Copernicus Books

| location=New York

| isbn=0-387-95436-8

| page=33}}

In 1920, Albert Michelson and Francis Pease mounted a 6-metre interferometer on the front of the 2.5-metre telescope at Mount Wilson Observatory. Helped by John Anderson, the trio measured the angular diameter of Betelgeuse at 0.047", a figure which resulted in a diameter of 3.84 × 10⁸ km (2.58 AU) based on the then-current parallax value of 0.018".{{cite journal

| author=Michelson, Albert Abraham; Pease, Francis G.

| title=Measurement of the diameter of alpha Orionis with the interferometer

| journal=Astrophysical Journal

| year=1921

| volume=53

| pages=249–59

| doi = 10.1086/142603

| bibcode = 1921ApJ....53..249M

| s2cid=21969744

| quote=The 0.047 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 arcseconds}} However there was known uncertainty owing to limb darkening and measurement errors—a central theme which would be the focus of scientific inquiry for almost a century. Beginning with this first angular measurement at visible wavelengths, researchers have since tried the measurement at other wavelengths with varying results.

The 1950s and '60s saw important scientific developments, the two Stratoscope projects and the 1958 publication of Structure and Evolution of the Stars, principally the work of Martin Schwarzschild and his close colleague at Princeton University, Richard Härm.{{cite web

| title=The Bruce Medalists

| work=Martin Schwarzschild 1965

| publisher=Astronomical Society of the Pacific (ASP)

| author=Tenn, Joseph S.

| url=http://www.phys-astro.sonoma.edu/BruceMedalists/

| year=2009

| month=June 09

| accessdate=28 September 2010}}{{cite book

| author=Schwarzschild, Martin

| title=Structure and Evolution of the Stars.

| publisher=Princeton University Press

| year=1958

| bibcode =1958ses..book.....S

| isbn=0-486-61479-4}} This book taught a generation of astrophysicists how to use budding computer technologies to create stellar models while the Stratoscope projects, by taking instrumented balloons above the Earth's turbulence, produced some of the finest images of solar granules and sunspots ever seen, thus confirming the existence of convection in the solar atmosphere. Both developments would prove to have a significant impact on our understanding of the structure of red supergiants like Betelgeuse.

File:Betelgeuse star (Hubble).jpg light by the Hubble Space Telescope and subsequently enhanced by NASA{{cite journal

| author=Gilliland, Ronald L.; Dupree, Andrea K.

| title=First Image of the Surface of a Star with the Hubble Space Telescope

| journal=Astrophysical Journal Letters

| year=1996

| date=May 1996

| volume=463

| issue=1

| pages=L29

| url=http://iopscience.iop.org/1538-4357/463/1/L29/pdf/5023.pdf

| accessdate=1 August 2010

| bibcode=1996ApJ...463L..29G

| doi=10.1086/310043

| s2cid=117717866

| quote=The yellow/red "image" or "photo" of Betelgeuse usually seen is actually not a picture of the red giant but rather a mathematically generated image based on the photograph. The photograph was actually of much lower resolution: The entire Betelgeuse image fit entirely within a 10x10 pixel area on the Hubble Space Telescopes Faint Object Camera. The actual images were oversampled by a factor of 5 with bicubic spline interpolation, then deconvolved.}}]]

The 1970s saw several notable advances in interferometry from the Berkeley Space Sciences Laboratory working in the infrared and Antoine Labeyrie in the visible, when researchers began to combine images from multiple telescopes and later invented "fringe-tracking" technology. But it was not until the late 1980s and early 1990s, when Betelgeuse became a regular target for aperture masking interferometry, that significant breakthroughs occurred in visible-light and infrared imaging. Pioneered by John E. Baldwin and other colleagues of the Cavendish Astrophysics Group, the new technique contributed some of the most accurate measurements of Betelgeuse to date while revealing a number of bright spots on the star's photosphere.{{cite journal

| author=Buscher, D. F.; Baldwin, J. E.; Warner, P. J.; Haniff, C. A.

| title=Detection of a bright feature on the surface of Betelgeuse

| journal=Monthly Notices of the Royal Astronomical Society

| year=1990

| volume=245

| page=7

| bibcode=1990MNRAS.245P...7B

| last2=Baldwin

| last3=Warner

| last4=Haniff}}{{cite journal

| author=Wilson, R. W.; Dhillon, V. S.; Haniff, C. A.

| title=The changing face of Betelgeuse

| journal=Monthly Notices of the Royal Astronomical Society

| year=1997

| volume=291

| page=819

| bibcode=1997MNRAS.291..819W

| last2=Dhillon

| last3=Haniff | issue=4

| doi=10.1093/mnras/291.4.819

}}{{cite journal

| author=Burns, D.

| title=The surface structure and limb-darkening profile of Betelgeuse

| journal=Monthly Notices of the Royal Astronomical Society

| year=1997

| date=September 1997

| volume=290

| issue=1

| pages=L11–L16

| bibcode=1997MNRAS.290L..11B

| last2=Baldwin

| last3=Boysen

| last4=Haniff

| last5=Lawson

| last6=MacKay

| last7=Rogers

| last8=Scott

| last9=Warner

| first2=J. E.

| first3=R. C.

| first4=C. A.

| display-authors=5

| first5=P. R.

| first6=C. D.

| first7=J.

| first8=T. R.

| first9=P. J.| doi=10.1093/mnras/290.1.L11

}} These were the first optical and infrared images of a stellar disk other than the Sun, first from ground-based interferometers and later from higher-resolution observations of the COAST telescope, with the "bright patches" or "hotspots" potentially corroborating a theory put forth by Schwarzschild decades earlier of massive convection cells dominating the stellar surface.{{cite journal

| title=Hotspots on late-type supergiants

| author=Tuthill, P. G.; Haniff, C. A.; Baldwin, J. E.

| journal=Monthly Notices of the Royal Astronomical Society

| volume=285

| issue=3

| pages=529–39

| year=1997

| date=March 1997

| bibcode=1997MNRAS.285..529T

| last2=Haniff

| last3=Baldwin| doi=10.1093/mnras/285.3.529

}}

In 1995, the Hubble Space Telescope's Faint Object Camera captured an ultraviolet image of comparable resolution—the first conventional-telescope image (or "direct-image" in NASA terminology) of the disk of another star. The image was taken at ultraviolet wavelengths since ground-based instruments cannot produce images in the ultraviolet with the same precision as Hubble. Like earlier pictures, this ultraviolet image also contained a bright patch indicating a region in the southwestern quadrant 2,000K hotter than the stellar surface.{{cite book

| author=Petersen, Carolyn Collins; Brandt, John C.

| title=Hubble Vision: Further Adventures with the Hubble Space Telescope

| publisher=Cambridge University Press

| location=Cambridge, England

| year=1998

| origyear=1995

| edition=2nd

| pages=91–92

| isbn=0-521-59291-7}} 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 North of about 55°.{{cite journal

| author=Uitenbroek, Han; Dupree, Andrea K.; Gilliland, Ronald L.

| title=Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of α Orionis

| journal=The Astronomical Journal

| year=1998

| volume=116

| issue=5

| pages=2501–12

| url=http://iopscience.iop.org/1538-3881/116/5/2501/fulltext

| doi=10.1086/300596

| bibcode=1998AJ....116.2501U

| s2cid=117596395

| accessdate=20 June 2007}}

{{Clear}}

File:Light curve of Betelgeuse.png V-band light curve of Betelgeuse (Alpha Orionis) from Dec. 1988 – Aug. 2002 ]] The first decade of the 21st century has witnessed major advances on multiple fronts, the most central of which have been the imaging of the star's photosphere at different wavelengths and the study of Betelgeuse's complex circumstellar shells. At the dawn of the millennium, the star's diameter was measured in the mid-infrared using the Infrared Spatial Interferometer (ISI) producing a limb darkened estimate of 55.2 ± 0.5 milliarcseconds (mas)—a figure entirely consistent with Michelson's findings eighty years earlier.{{cite journal

| last1=Weiner | first1 = J.

| title=Precision Measurements of the Diameters of α Orionis and ο Ceti at 11 Microns

| journal=The Astrophysical Journal

| year=2000 | date=December 2000

| volume=544

| issue=2

| pages=1097–1100

| url=http://iopscience.iop.org/0004-637X/544/2/1097/pdf/52233.web.pdf

| bibcode=2000ApJ...544.1097W

| doi=10.1086/317264

| accessdate=23 June 2007

| last2=Danchi

| first2=W. C.

| last3=Hale

| first3=D. D. S.

| last4=McMahon

| first4=J.

| display-authors=4

| last5=Townes

| first5=C. H.

| last6=Monnier

| first6=J. D.

| last7=Tuthill

| first7=P. G.| s2cid = 11697011

}} At the time of its publication, the estimated parallax from the Hipparcos mission was 7.63 ± 1.64 mas, yielding an estimated radius for Betelgeuse of 3.6 AU. However, numerous interferometric studies in the near-infrared have appeared since from the Paranal Observatory in Chile arguing for much tighter diameters. Nevertheless, on June 9, 2009, Nobel Laureate Charles Townes announced that the star had shrunk 15% since 1993 at an increasing rate without a significant diminution in magnitude{{cite web

| title=Red Giant Star Betelgeuse Mysteriously Shrinking

| author=Sanders, Robert

| date=9 June 2009

| work=UC Berkeley News

| publisher=UC Berkeley

| url=http://www.berkeley.edu/news/media/releases/2009/06/09_betelim.shtml

| accessdate=18 April 2010}} Subsequent observations suggest that the apparent contraction may be due to shell activity in the star's extended atmosphere.{{cite journal

| author=Ravi, V.; Wishnow, E.; Lockwood, S.; Townes, C.

| title=The Many Faces of Betelgeuse

| journal=Astronomical Society of the Pacific

| year=2011

| date=December 2011

| pages=1025

| url=http://arxiv.org/pdf/1012.0377v1.pdf

| bibcode=2011ASPC..448.1025R

| accessdate=5 July 2012|arxiv = 1012.0377

| last2=Wishnow

| last3=Lockwood

| last4=Townes

| volume=448 }}

Enveloping this whole discussion have been numerous inquiries into the abstruse dynamics of Betelgeuse's extended atmosphere. The mass that makes up galaxies is recycled as stars are formed and destroyed. For decades astronomers have understood that the outer shells of red giants are central to this process, yet the actual mechanics of stellar mass loss remain a mystery.

{{cite journal

| title=The Circumstellar Shells and Mass Loss Rates of Four M Supergiants

| author=Bernat, Andrew P.

| journal=Astrophysical Journal

| volume=213

| pages=756–66

| year=1977

| bibcode=1977ApJ...213..756B

| doi=10.1086/155205

| s2cid=121146305

}} With recent advances in interferometric methodologies, astronomers may be close to resolving this conundrum. In July 2009, images released by the European Southern Observatory, taken by the ground-based Very Large Telescope Interferometer (VLTI), showed a vast plume of gas being ejected into the surrounding atmosphere with distances approximating 30 AU.{{cite journal

| author=Kervella, P.

| title=The Close Circumstellar Environment of Betelgeuse. Adaptive Optics Spectro-imaging in the Near-IR with VLT/NACO

| journal=Astronomy and Astrophysics

| year=2009

| date=September 2009

| volume=504

| issue=1

| pages=115–25

| url=http://arxiv.org/pdf/0907.1843v1.pdf

| accessdate=10 July 2010

| bibcode=2009A&A...504..115K

| doi=10.1051/0004-6361/200912521

| last2=Verhoelst

| first2=T.

| last3=Ridgway

| first3=S. T.

| last4=Perrin

| first4=G.

| display-authors=5

| last5=Lacour

| first5=S.

| last6=Cami

| first6=J.

| last7=Haubois

| first7=X.|arxiv = 0907.1843 | s2cid=14278046

}}{{cite web

| title=Sharpest Views of Betelgeuse Reveal How Supergiant Stars Lose Mass

| date=29 July 2009

| work=Press Releases

| publisher=European Southern Observatory

| url=http://www.eso.org/public/news/eso0927/

| accessdate=6 September 2010}} Comparable to the distance between the Sun and Neptune, this mass ejection is but one of multiple dynamics occurring in the surrounding atmosphere. Astronomers have identified at least six different shells surrounding Betelgeuse. Solving the mystery of mass loss in the late stages of a star's evolution may reveal those factors which precipitate the explosive deaths of these stellar giants.

File:Orion Head to Toe.jpg showing Betelgeuse in relationship to the dense nebulas of the Orion Molecular Cloud Complex and the Belt of Orion]]

Betelgeuse is easy to spot in the night sky, as it appears in proximity to the famous belt of Orion and has a distinctive orange-red color to the naked eye. In the Northern Hemisphere, beginning in January of each year, it can be seen rising in the east just after sunset. By mid-March, it is visible to virtually every inhabited region of the globe, with only a few research stations in Antarctica at latitudes south of 82° unable to see it. Once May arrives, the red giant can be glimpsed but briefly on the western horizon just after sunset, reappearing again a few months later on the eastern horizon before sunrise.

The apparent magnitude of Betelgeuse is listed in SIMBAD at 0.42, making it on average the eighth brightest star in the celestial sphere excluding the Sun—just ahead of Achernar. Because Betelgeuse is a variable star whose brightness ranges between 0.2 and 1.2, there are periods when it will surpass Procyon to become the seventh brightest star. Occasionally it can even outshine Rigel and become the sixth brightest star, as the latter star, with a nominal apparent magnitude of 0.12, has been reported to fluctuate slightly in brightness, by 0.03 to 0.3 magnitudes.{{cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=V/50/catalog&recno=1713 |title= HR 1713, database entry |work= The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version)|author=Hoffleit, D.; Warren, W. H. Jr.| publisher= CDS ID [http://vizier.u-strasbg.fr/viz-bin/Cat?V/50 V/50] |accessdate= 19 August 2010}} At its faintest, Betelgeuse will fall behind Deneb as the 19th brightest star and compete with Mimosa for the 20th position. File:ESO-Betelgeuse.jpg's Very Large Telescope showing not only the stellar disk, but also an extended atmosphere with a previously unknown plume of surrounding gas]]

Betelgeuse has a color index (B–V) of 1.85—a figure which points to the advanced "redness" of this celestial object. The photosphere has an extended atmosphere which displays strong lines of emission rather than absorption, a phenomenon which occurs when a star is surrounded by a thick gaseous envelope. This extended gaseous atmosphere has been observed moving both away from and towards Betelgeuse, depending on radial velocity fluctuations in the photosphere. Betelgeuse is the brightest near-infrared source in the sky with a J band magnitude of −2.99.{{cite web

|date=7 September 2009

|title=Very Bright Stars in the 2MASS Point Source Catalog (PSC)

|publisher=The Two Micron All Sky Survey at IPAC

|author=R. Cutri and M. Skrutskie

|url=http://www.ipac.caltech.edu/2mass/releases/allsky/doc/sec1_6b.html#satr1

|accessdate=28 December 2011}} As a result, only about 13% of the star's radiant energy is emitted in the form of visible light. If human eyes were sensitive to radiation at all wavelengths, Betelgeuse would appear as the brightest star in the sky.

Since the first successful parallax measurement by Friedrich Bessel in 1838, astronomers have been puzzled by Betelgeuse's distance. Solving this enigma holds the key to understanding other stellar parameters, since an accurate "distance leads to the luminosity and when combined with an angular diameter gives the physical radius and effective temperature; luminosity and isotopic abundances provide estimates of the stellar age and mass".{{cite journal

| author=Harper, Graham M.; Brown, Alexander; Guinan, Edward F.

| title=A New VLA-Hipparcos Distance to Betelgeuse and its Implications

| journal=The Astronomical Journal

| year=2008

| date=April 2008

| volume=135

| issue=4

| pages=1430–40

| url=http://iopscience.iop.org/1538-3881/135/4/1430/pdf/aj_135_4_1430.pdf

| accessdate=10 July 2010

| bibcode=2008AJ....135.1430H

| doi=10.1088/0004-6256/135/4/1430| s2cid=34660949

}} In 1920, when the first interferometric studies were performed on the star's diameter, the assumed parallax was 0.0180 arcseconds. That equated to a distance of 56 parsecs (pc) or roughly 180 light-years (ly) and produced not only an inaccurate radius for the star, but every other stellar characteristic. Since then, there has been ongoing work to measure the actual distance of Betelgeuse, with proposed distances as high as 400 pc or about 1,300 ly.

Before the publication of the Hipparcos Catalogue (1997), there were two conflicting parallax measurements for Betelgeuse. The first was the Yale University Observatory (1991) with a published parallax of π = 9.8 ± 4.7 mas, yielding a distance of roughly 102 pc or 330 ly.{{cite journal

| author=van Altena, W. F.; Lee, J. T.; Hoffleit, D.

| title=Yale Trigonometric Parallaxes Preliminary

| journal=Yale University Observatory (1991)

| year=1995

| date=October 1995

| bibcode=1995yCat.1174....0V

| last2=Lee

| last3=Hoffleit

| volume=1174

| pages=0}} The second was the Hipparcos Input Catalogue (1993) with a trigonometric parallax of π = 5 ± 4 mas, a distance of 200 pc or 650 ly—almost twice the Yale estimate.{{cite web

| title=Hipparcos Input Catalogue, Version 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

| accessdate=20 June 2010}} With such uncertainty, researchers were adopting a wide range of distance estimates, leading to significant variances in the calculation of the star's attributes.File:USA.NM.VeryLargeArray.02.jpg's Very Large Array used to derive Betelgeuse's current distance estimate]]

The results from the Hipparcos mission were released in 1997. The measured parallax of Betelgeuse was π = 7.63 ± 1.64 mas, which equated to a distance of 131 pc or roughly 430 ly, and had a smaller reported error than previous measurements.{{Cite journal | display-authors=1 | 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}} However, later evaluation of the Hipparcos parallax measurements for variable stars like Betelgeuse found that the uncertainty of these measurements were underestimated.{{cite journal

| author=Eyer, L.; Grenon, M.

| title=Problems Encountered in the Hipparcos Variable Stars Analysis

| journal=Delta Scuti and Related Stars, Reference Handbook and Proceedings of the 6th Vienna Workshop in Astrophysics

| year=2000

| series=ASP Conference Series

| volume=210

| bibcode=2000ASPC..210..482E

| isbn=1-58381-041-2|arxiv = astro-ph/0002235

| last2=Grenon

| page=482 }} In 2007, Floor van Leeuwen improved upon the Hipparcos parallax, producing a new figure of π = 6.55 ± 0.83, hence a much tighter error factor yielding a distance of roughly 152 ± 20pc or 520 ± 73ly.{{cite journal | title=Hipparcos, the New Reduction | last1=van Leeuwen | first1=F | year=2007 | date=November 2007 | work=VizieR | publisher=Centre de Données astronomiques de Strasbourg | pages=653 | issue=2 | volume=474 | doi=10.1051/0004-6361:20078357 | journal=Astronomy and Astrophysics | bibcode=2007A&A...474..653V |arxiv = 0708.1752| s2cid=18759600 }}

In 2008, Graham Harper, using the Very Large Array (VLA), produced a radio solution of π = 5.07 ± 1.10 mas, equaling a distance of 197 ± 45 pc or 643 ± 146 ly. As Harper points out: "The revised Hipparcos parallax leads to a larger distance (152 ± 20 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 suffer from systematic errors as well, the Harper solution combines both datasets in the hope of mitigating such errors.

The next breakthrough will likely come from the European Space Agency's upcoming Gaia mission when it undertakes a detailed analysis of physical properties for each star observed, revealing luminosity, temperature, gravity and composition. Gaia will achieve this by repeatedly measuring the positions of all objects down to magnitude 20, and those brighter than magnitude 15, to an accuracy of 24 microarcseconds—akin to measuring the diameter of a human hair from 1000 km away. On-board detection equipment will ensure that variable stars like Betelgeuse will all be detected to this faint limit, thus addressing most of the limitations of the earlier Hipparcos mission.{{cite web

|title=Gaia Overview

|publisher=European Space Agency

|url=http://www.esa.int/esaSC/120377_index_0_m.html

|date=Last update: 4 May 2010

|accessdate=14 July 2010}}

File:Betelgeuse pulsating UV (HST).jpg

Betelgeuse is classified as a semiregular variable star of subgroup SRc; these are pulsating red supergiants with low amplitude variations and periods of stable brightness. Different hypotheses have been put forward to explain Betelgeuse's volatile choreography—a phenomenon which causes an absolute magnitude oscillation from −5.27 and −6.27.This range of absolute magnitudes assumes an apparent magnitude that varies from 0.2 to 1.2 and a distance of 197 pc. Established theories of stellar structure suggest that the outer layers of this supergiant gradually expand and contract, causing the surface area (photosphere) to alternately increase and decrease, and the temperature to rise and fall—thereby eliciting the measured cadence in the star's brightness between its dimmest magnitude of 1.2, seen as early as 1927, and its brightest of 0.2, seen in 1933 and 1942. A red supergiant like Betelgeuse will pulsate this way because its stellar atmosphere is inherently unstable. As the star contracts, it absorbs more and more of the energy that passes through it, causing the atmosphere to heat up and expand. Conversely, as the star expands, its atmosphere becomes less dense allowing the energy to escape and the atmosphere to cool, thus initiating a new contraction phase. Calculating the star's pulsations and modeling its periodicity have been difficult, as it appears there are several cycles interlaced. As discussed in papers by Stebbins and Sanford in the 1930s, there are short-term variations of around 150 to 300 days that modulate a regular cyclic variation with a period of roughly 5.7 years.{{cite journal

| author=Goldberg, Leo

| title=The Variability of Alpha Orionis

| journal=Publications of the Astronomical Society of the Pacific

| year=1984

| volume=96

| pages=366–71

| bibcode=1984PASP...96..366G

| doi=10.1086/131347| s2cid=121926262

}}

File:Sun diagram.svg showing photospheric granules :
1. Core
2. Radiative zone
3. Convective zone
4. Photosphere
5. Chromosphere
6. Corona
7. Sunspot
8. Granules
9. Prominence ]]

In fact, the supergiant consistently displays irregular photometric, polarimetric and spectroscopic variations, phenomena which point to complex activity on the star's surface and its extended atmosphere. In marked contrast to most giant stars that are typically long period variables with reasonably regular periods, red giants are generally semiregular or irregular with pulsating characteristics. Martin Schwarzschild in 1975 attributed these brightness fluctuations to the changing granulation pattern formed by a few giant convection cells covering the surface of these stars.{{cite journal

| author=Schwarzschild, Martin

| title=On the Scale of Photospheric Convection in Red Giants and Supergiants

| journal=Astrophysical Journal

| year=1975

| volume=195

| issue=1

| pages=137–44

| bibcode=1975ApJ...195..137S

| doi=10.1086/153313}}{{cite journal

| title=Spots on the Surface of Betelgeuse – Results from New 3D Stellar Convection Models

| author=Freytag, B.; Steffen, M.; Dorch, B.

| journal=Astronomische Nachrichten

| year=2002

| date=July 2002

| volume=323

| issue=3/4

| pages=213–19

| bibcode=2002AN....323..213F

| doi=10.1002/1521-3994(200208)323:3/4<213::AID-ASNA213>3.0.CO;2-H

}} For the Sun, these convection cells, otherwise known as solar granules, represent the foremost mode of heat transfer—hence those convective elements which dominate the brightness variations in the solar photosphere. The typical diameter for a solar granule is about 2,000 km (a surface area roughly the size of India), with an average depth of 700 km. With a surface of roughly 6 trillion km², there are about 2 million such granules lying on the Sun's photosphere, which because of their number produce a relatively constant flux.{{cite journal

| author=Leighton, Robert B.

| title=Transport of Magnetic Fields on the Sun

| journal=Astrophysical Journal

| year=1964

| volume=140

| page=1547

| bibcode=1964ApJ...140.1547L

| doi=10.1086/148058}} By contrast, Schwarzschild argues that stars like Betelgeuse may have only a dozen monster granules with diameters of 180 million km or more dominating the surface of the star with depths of about 60 million km, which, because of the very low temperatures and extremely low density found in red giant envelopes, result in convective inefficiency. Consequently, if only a third of these convective cells are visible to us at any one time, the time variations in their observable light may well be reflected in the irregular brightness variations of the integrated light of the star.

The hypothesis that gigantic convection cells dominate the surface of red giants and supergiants remains accepted by the astronomical community. When the Hubble Space Telescope captured its first direct image of Betelgeuse in 1995 revealing a mysterious hot spot, astronomers attributed it to convection.{{cite journal

| author=Dupree, Andrea K.; Gilliland, Ronald L.

| title=HST Direct Image of Betelgeuse

| journal=Bulletin of the American Astronomical Society

| year=1995

| date=December 1995

| volume=27

| page=1328

| bibcode=1995AAS...187.3201D

| quote=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."

| last2=Gilliland}} Two years later, astronomers observed intricate asymmetries in the brightness distribution of the star revealing at least three bright spots, the magnitude of which was "consistent with convective surface hotspots". Then in 2000, another team of astronomers led by Alex Lobel of the Harvard–Smithsonian Center for Astrophysics (CfA) noted that Betelgeuse exhibits raging storms of hot and cold gas in its turbulent atmosphere. The team surmised that huge areas of the star's photosphere vigorously bulge out in different directions at times, ejecting long plumes of warm gas into the cold dust envelope. Another explanation that was also given was the occurrence of shock waves caused by warm gas traversing cooler regions of the star.{{cite web

|title=Betelgeuse; Release No.: 04-03

|author=SolStation

|publisher=Sol Company

|url=http://www.nova.org/~sol/solcom/x-objects/betelgeuse.htm

|accessdate=20 July 2010}}{{cite web

|title=Storms Of Hot And Cold Gas Rage In Betelgeuse's Turbulent Atmosphere

|publisher=Harvard–Smithsonian Center for Astrophysics

|author=Aguilar, David; Pulliam, Christine; Lobel, A.

|year=2004

|month=January 6, 9:20 a.m. EST

|url=http://www.cfa.harvard.edu/news/archive/pr0403.html

|accessdate=27 July 2010}} The team investigated the atmosphere of Betelgeuse over a period of five years between 1998 and 2003 with the Space Telescope Imaging Spectrograph aboard Hubble. They found that the bubbling action of the chromosphere tosses gas out one side of the star, while it falls inward at the other side, similar to the slow-motion churning of a lava lamp.

{{seealso|List of largest known stars}}

A third challenge that has confronted astronomers has been measuring the star's angular diameter. On December 13, 1920, Betelgeuse became the first star outside the Solar System to ever have its photosphere measured. Although interferometry was still in its infancy, the experiment proved a success and Betelgeuse was found to have a uniform disk of 0.047 arcseconds. The astronomers' insights on limb darkening were noteworthy; in addition to a measurement error of 10%, the team concluded that the stellar disk was likely 17% larger due to the diminishing intensity of light around the edges—hence an angular diameter of about 0.055".{{cite journal

| title= A Systematic Change with Time in the Size of Betelgeuse

| author=Townes, C. H.; Wishnow, E. H.; Hale, D. D. S.; 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| s2cid=121009337

}} Since then, there have been other studies conducted, which have produced angles that range from 0.042 to 0.069 arcseconds.{{cite journal

| author=Bonneau, D.; Labeyrie, A.

| title=Speckle Interferometry: Color-Dependent Limb Darkening Evidenced on Alpha Orionis and Omicron Ceti

| journal=Astrophysical Journal

| year=1973

| volume= 181

| page=L1

| bibcode=1973ApJ...181L...1B

| doi=10.1086/181171}}{{cite journal

| author=Balega, Iu.; Blazit, A.; Bonneau, D.; Koechlin, L.; Labeyrie, A.; Foy, R..

| title=The angular diameter of Betelgeuse

| journal=Astronomy and Astrophysics

| date=November 1982

| volume=115

| issue= 2

| year=1982

| pages=253–56

| bibcode=1982A&A...115..253B

| last2=Blazit

| last3=Bonneau

| last4=Koechlin

| last5=Labeyrie

| last6=Foy

}} Combining that data with historical distance estimates of 180 to 815 ly yields a projected diameter of the stellar disk of anywhere from 2.4 to 17.8 AU, hence a radius of 1.2 to 8.9 AU respectively.The following table provides a non-exhaustive list of angular measurements conducted since 1920. Also included is a column providing a current range of radii for each study based on Betelgeuse's most recent distance estimate (Harper et al) of 197±45 pc:

¹The final year of observations, unless otherwise noted.

²Uniform disk measurement, unless otherwise noted.

³Radii calculations use the same methodology as outlined in Note #2 below ^‡Limb darkened measurement.

Using the Solar System as a yardstick, the orbit of Mars is about 1.5 AU, Ceres in the asteroid belt 2.7 AU, Jupiter 5.5 AU—consequently a photosphere which, depending on Betelgeuse's actual distance from Earth, could well extend beyond the Jovian orbit but not quite as far as Saturn at 9.5 AU. File:Betelgeuse radio wavelengths.jpg

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

1. The rhythmic expansion and contraction of the photosphere, as theory suggests, means the diameter is never constant;
2. There is no definable "edge" to the star as limb darkening causes the optical emissions to vary in color and decrease the farther one extends out from the center;
3. Betelgeuse is surrounded by a circumstellar envelope composed of matter being ejected from the star—matter which both absorbs and emits light—making it difficult to define the actual surface of the star;
4. Measurements can be taken at varying wavelengths within the electromagnetic spectrum, with each wavelength revealing something different. Studies have shown that angular diameters are considerably larger at visible wavelengths, decrease to a minimum in the near-infrared, only to increase again in the mid-infrared.{{cite journal

| title=Interferometric Observations of the Supergiant Stars α Orionis and α Herculis with FLUOR at IOTA

| author=Perrin, G.; Ridgway, S. T.; Coudé du Foresto, V.; Mennesson, B.; Traub, W. A.; 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 AU or 920 R_☉|arxiv = astro-ph/0402099 | s2cid=18648216

}}{{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 interferometers

|accessdate=21 June 2007}} The difference in reported diameters can be as much as 30–35%, yet because each wavelength measures something different, comparing one finding with another is difficult;

1. Atmospheric twinkling limits the resolution obtainable from ground-based telescopes since turbulence degrades angular resolution.

To overcome these challenges, researchers have employed various solutions. Astronomical interferometry, first conceived by Hippolyte Fizeau in 1868, was the seminal concept that revolutionized modern telescopy and lead to the creation of the Michelson interferometer in the 1880s, and the first successful measurement of Betelgeuse.{{cite journal

| author=Perrin, Guy; Malbet, Fabien

| title=Observing with the VLTI

| journal=EAS Publications Series

| year=2003

| volume= 6

| bibcode=2003EAS.....6D...3P

| last2=Malbet

| pages=3

| doi=10.1051/eas/20030601}} Just as human depth perception increases when two eyes perceive an object instead of one, Fizeau proposed the observation of stars through two apertures instead of one to obtain interferences that would furnish information on the star's spatial intensity distribution. The science evolved quickly where today multiple-aperture interferometers are now used to capture numerous speckled images, which are then synthesized using Fourier analysis to produce a portrait of extraordinary resolution.{{cite web

| author=Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

| title=3 Auxiliary Telescopes

| work=Today's Astronomy Picture of the Day

| date=21 April 2012

| url=http://apod.nasa.gov/apod/ap120421.html

| accessdate=17 August 2012

| quote=Photograph showing three of the four enclosures which house 1.8 meter Auxiliary Telescopes (ATs) at the Paranal Observatory in the Atacama Desert region of Chile.}} It was this methodology that identified the hotspots on Betelgeuse in the 1990s.{{cite journal

| author=Worden, S.

| title=Speckle Interferometry

| journal=New Scientist

| year=1978

| volume=78

| pages=238–40

| bibcode=1978NewSc..78..238W}} Other technological breakthroughs include adaptive optics,{{cite journal

| title=Ground-Based Interferometry with Adaptive Optics

| author=Roddier, F.

| journal=Working on the Fringe: Optical and IR Interferometry from Ground and Space. Proceedings from ASP Conference

| volume=194

| year=1999

| isbn=1-58381-020-X

| bibcode=1999ASPC..194..318R

| pages=318}} space observatories like Hipparcos, Hubble and Spitzer,{{cite web

| title=Top Five Breakthroughs From Hubble's Workhorse Camera

| date=4 May 2009

| url=http://www.jpl.nasa.gov/news/features.cfm?feature=2132

| publisher=NASA Jet Propulsion Laboratory, California Institute of Technology

|accessdate=28 August 2007}} and the Astronomical Multi-BEam Recombiner (AMBER), which combines the beams of three telescopes simultaneously, allowing researchers to achieve milliarcsecond spatial resolution.{{cite web

| author=Melnick, J.; Petrov R.; Malbet, 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

|accessdate=29 August 2007}}{{cite web

| title=MIDI and AMBER from the User's Point of View

| author=Wittkowski, M.

| date=23 February 2007

| url=http://www.vlti.org/events/assets/1/proceedings/2.4_Wittkowski.pdf

| publisher=European Southern Observatory VLTI

|accessdate=29 August 2007}}

The current debate revolves around which wavelength—the visible, near-infrared (NIR) or mid-infrared (MIR)—produces the most accurate angular measurement. In 1996, Manfred Bester, working with the ISI in the mid-infrared, led a team at the Space Sciences Laboratory (SSL) at U.C. Berkeley to produce a solution showing Betelgeuse with a uniform disk of 56.6 ± 1.0 mas. In 2000, the SSL team produced another measure of 54.7 ± 0.3 mas, ignoring any possible contribution from hotspots, which are less noticeable in the mid-infrared. Also included was a theoretical allowance for limb darkening yielding a diameter of 55.2 ± 0.5 mas. The Bester estimate equates to a radius of roughly 5.6 AU or 1,200 R_☉, assuming the 2008 Harper distance of 197.0 ± 45 pc,{{cite journal

| author=Smith, Nathan; Hinkle, Kenneth H.; 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

| year=2009

| date=March 2009

| volume=137

| issue=3

| pages=3558–3573

| url=http://arxiv.org/pdf/0811.3037v1.pdf

| arxiv=0811.3037

| accessdate=9 September 2012

| doi=10.1088/0004-6256/137/3/3558

| bibcode=2009AJ....137.3558S| s2cid=19019913

}}For detailed computations of stellar radius and implications relating to the star's luminosity, see the Computational challenges section in the Luminosity article. a figure roughly the size of the Jovian orbit of 5.5 AU, published in 2009 in Astronomy Magazine and a year later in NASA's Astronomy Picture of the Day.{{cite journal

| title=Red Giant Star Betelgeuse in the Constellation Orion is Mysteriously Shrinking

| journal=Astronomy Magazine

| year=2009

| url=http://www.astronomy.com/en/News-Observing/News/2009/06/Red%20giant%20star%20Betelgeuse%20in%20the%20constellation%20Orion%20is%20mysteriously%20shrinking.aspx

| accessdate=14 September 2012}}{{cite web| author=Robert Nemiroff (MTU) & Jerry Bonnell (USRA) | title=The Spotty Surface of Betelgeuse | work=Today's Astronomy Picture of the Day | date=6 January 2010 | url=http://apod.nasa.gov/apod/ap100106.html | accessdate=18 July 2010}}

Across the Atlantic, another team of astronomers working in the near-infrared and led by Guy Perrin of the Observatoire de Paris produced a 2004 document arguing that the more accurate photospheric measurement was 43.33 ± 0.04 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 and 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. Comparing studies, however, is problematic since each wavelength produces a different view of the star, requiring different interpretations.File:Orion's Big Head Revealed in Infrared.jpg and Bellatrix with surrounding nebulas{{cite web

|title=Orion's Big Head Revealed in Infrared

|author=NASA/JPL-Caltech/UCLA

|publisher=NASA Mission News

|url=http://www.nasa.gov/mission_pages/WISE/multimedia/gallery/pia14040.html

|date=Last update: 18 April 2011

|accessdate=12 June 2012}}]]

Studies done in 2009 with the IOTA and VLTI brought strong support to Perrin's analysis yielding diameters ranging from 42.57 to 44.28 mas with comparatively insignificant margins of error.{{cite journal

| author=Hernandez Utrera, O.; 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

| last2=Chelli

}}{{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 | s2cid=118593802

}} In 2011, Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy produced a third estimate in the near-infrared corroborating Perrin's numbers, this time showing a limb-darkened disk diameter of 42.49 ± 0.06 mas.{{cite journal

| author=Ohnaka, K.; Weigelt, G.; Millour, F.; Hofmann, K.-H.; Driebe, T.; Schertl, D.; Chelli, A.; Massi, F.; Petrov, R.; Stee, Ph.

| title=Imaging the Dynamical Atmosphere of the Red Supergiant Betelgeuse in the CO First Overtone Lines with VLTI/AMBER

| journal=Astronomy & Astrophysics

| year=2011

| date=May 2011

| volume=529, id.A163

| pages=A163

| url=http://arxiv.org/pdf/1104.0958v1.pdf

| arxiv=1104.0958

| accessdate=14 September 2012

| doi=10.1051/0004-6361/201016279

| bibcode=2011A&A...529A.163O

| s2cid=56281923

| quote="We derive a uniform-disk diameter of 42.05 ± 0.05 mas and a power-law-type limb-darkened disk diameter of 42.49 ± 0.06 mas and a limb-darkening parameter of (9.7 ± 0.5) × 10^-2"}} Consequently, if we combine the smaller Hipparcos distance from van Leeuwen of 152 ± 20 pc with Perrin's angular measurement of 43.33 mas, a near-infrared photospheric estimate would equate to about 3.4 AU or 730 R_☉.{{cite journal

| author=Kervella, P.; Perrin, G.; Chiavassa, A.; Ridgway, S. T.; Cami, J.; Haubois, X.; 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

| pages=A117

| url=http://arxiv.org/pdf/1106.5041v1.pdf

| arxiv=1106.5041

| accessdate=14 September 2012

| doi=10.1051/0004-6361/201116962

| bibcode=2011A&A...531A.117K| s2cid=119190969

}}

Central to this discussion is another paper published by the Berkeley team in 2009, this time led by Charles Townes, reporting that the radius of Betelgeuse had actually shrunk from 1993 to 2009 by 15%, with the 2008 angular measurement equal to 47.0 mas, not too far from Perrin's estimate.{{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.}} Unlike most papers heretofore published, 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 ± 0.1 mas seen in 1993 to 47.0 ± 0.1 mas seen in 2008—a contraction of almost 0.9 AU in 15 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. Other possible explanations are photospheric protrusions due to convection or a star that is not spherical but rather asymmetric causing the appearance of expansion and contraction as the star rotates on its axis.{{cite web

| author=Courtland, Rachel

| year=2009

| url=http://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}}

In conclusion, the current debate 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, is yet to be resolved. 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. This conclusion, if further corroborated, would suggest an average angular diameter for Betelgeuse closer to Perrin's estimate at 43.33 arcseconds, hence a stellar radius of about 3.4 AU (730 R_☉), if we assume the shorter Hipparcos distance of 498 ± 73 ly in lieu of Harper's estimate at 643 ± 146 ly. The Gaia spacecraft will likely clarify many of the assumptions presently used in calculating the size of Betelgeuse's stellar disk, yielding a much wider consensus among astronomers.

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 57.0 ± 0.5 mas. Betelgeuse is now considered to be in third place, although R Doradus, being much closer to Earth at about 200 ly, has an actual diameter roughly one-third that of Betelgeuse.{{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

}}

Since 1943, the spectrum of Betelgeuse has served as one of the stable anchor points by which other stars are classified.{{Cite journal

| last1=Garrison | first1=R. F.

| title=Anchor Points for the MK System of Spectral Classification

| journal=Bulletin of the American Astronomical Society | volume=25

| page=1319| year=1993 | bibcode=1993AAS...183.1710G

| url=http://www.astro.utoronto.ca/~garrison/mkstds.html

| accessdate=4 February 2012

}} Its spectral class of M2Iab, signifies that it is a red Class M star;{{cite web

| url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=betelgeuse

| title =SIMBAD Query Result: BETELGEUSE – Semi-regular Pulsating Star

| publisher=Centre de Données astronomiques de Strasbourg

| accessdate=20 June 2007}} the "ab" suffix, derived from the Yerkes spectral classification system, indicates that it is an intermediate luminous supergiant. Uncertainties regarding the star's surface temperature, angular diameter and distance, make it very difficult to achieve a precise measurement of Betelgeuse's luminosity. Current research gives Betelgeuse an average luminosity of 120,000 ± 30,000 L_☉, assuming a median temperature of 3,300 K and a radius of 1,200 R_☉. However, with most of the star's radiant energy occurring in the infrared and a substantial amount being absorbed by circumstellar matter, the human eye simply cannot perceive the star's intrinsic brightness.

Because the existence of stellar companions has never been confirmed, there is no direct method of measuring Betelgeuse's mass.{{cite journal

| author=Neilson, H. R.; Lester, J. B.; Haubois, X.

| title=Weighing Betelgeuse: Measuring the Mass of α Orionis from Stellar Limb-darkening

| journal=Astronomical Society of the Pacific

| pages = 117

| year=2011

| date=December 2011

| volume=9th Pacific Rim Conference on Stellar Astrophysics. Proceedings of a conference held at Lijiang, China in 14-20 April 2011. ASP Conference Series, Vol. 451

| url=http://arxiv.org/pdf/1109.4562v1.pdf

| arxiv = 1109.4562

| accessdate=9 September 2012

| bibcode = 2010ASPC..425..103L}} A mass estimate is only possible using theoretical modeling, a situation which has produced mass estimates ranging from 5—30 M_☉ in the last decade.{{cite arXiv

| title=Dark Supergiant: Chandra's Limits on X-rays from Betelgeuse

| author=Posson-Brown, Jennifer; Kashyap, Vinay L.; Pease, Deron O.; Drake, Jeremy J.

| year=2006

| eprint=astro-ph/0606387

| class=astro-ph}}{{cite journal

| title=Betelgeuse and Its Variations

| author=Gray, David F.

| journal=The Astrophysical Journal

| volume= 532

| issue=1

| pages=487–96

| year=2000

|url=http://iopscience.iop.org/0004-637X/532/1/487/pdf/40185.web.pdf

| doi=10.1086/308538

| bibcode=2000ApJ...532..487G

| s2cid=121170944

| quote=The mass of the star is unknown, but most investigators show a preference for a fairly large mass in the range of 10–20 M_☉}} Smith and colleagues calculated that Betelgeuse began its life as a star of 15 to 20 M_⊙, based on a photospheric measurement of 5.6 AU or 1,200 R_⊙.{{cite journal

| author=Smith, Nathan; Hinkle, Kenneth H.; 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

| year=2009

| volume=137

| issue=3

| pages=3558–3573

| url=http://arxiv.org/pdf/0811.3037v1.pdf

| arxiv=0811.3037

| accessdate=9 September 2012

| doi=10.1088/0004-6256/137/3/3558

| bibcode=2009AJ....137.3558S| s2cid=19019913

}} However, a novel method of determining the supergiant's mass was proposed in 2011 by Hilding Neilson and colleagues, arguing for a stellar mass of 11.6 M_⊙ with an upper limit of 16.6 and lower of 7.7 M_⊙, based on observations of the star’s intensity profile from narrow H-band interferometry and using a photospheric measurement of roughly 4.3 AU or 955 R_⊙. How the debate will be resolved is still open to question—at least until a companion star is identified allowing for a direct calculation of stellar mass.

Typical of red supergiants, Betelgeuse is a cool star. Because of its variability and the presence of hotspots, the photospheric temperature is somewhat uncertain. Studies in the last decade report temperatures ranging from 3,140 to 3,641 K with a median of about 3,300K. The star is also a slow rotator, with the most recent velocity recorded at 5 km/s. Depending on its photospheric radius, it could take the star anywhere from 25 to 32 years to turn on its axis—much slower than Antares which has a rotational velocity of 20 km/s.{{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

|accessdate=07 September 2012}}

In 2002, astronomers using sophisticated computer simulations began to speculate that Betelgeuse might exhibit 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.{{cite journal

| title=Magnetic Activity in Late-type Giant Stars: Numerical MHD Simulations of Non-linear Dynamo Action in Betelgeuse

| author=Dorch, S. B. F.

| journal=Astronomy & Astrophysics

| volume= 423

| issue=3

| pages=1101–07

| year=2004

|url=http://www.astro.ku.dk/~dorch/paper/copies/Dorch2004.pdf

| doi=10.1051/0004-6361:20040435

| bibcode=2004A&A...423.1101D|arxiv = astro-ph/0403321 | s2cid=16240922

}} A series of 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.

{{cite journal

| title=The Magnetic Field of Betelgeuse : a Local Dynamo from Giant Convection Cells?

| author=Aurière, M; Donati, J.-F.; Konstantinova-Antova, R.; Perrin, G. ;Petit, P.; Roudier, T.

| journal=Astronomy & Astrophysics

| year=2010

| volume=516

| page=L2

| arxiv=1005.4845

| bibcode=2010A&A...516L...2A

| doi=10.1051/0004-6361/201014925

| s2cid=54943572

}}

File:Orion OB1 & 25 Ori Group.png

The kinematics of Betelgeuse are not easily explained. The age of Class M supergiants with an initial mass of 20 M_☉ is roughly 10 million years.

{{cite journal

| title= The Role of Rotation and Mass Loss in the Evolution of Massive Stars

| author= Maeder, André; Meynet, Georges

| journal=Publications of the Astronomical Society of the Pacific

| page=267

| year=2003

| bibcode=2003IAUS..212..267M

| last2= Meynet

| volume= 212

}} Given its current space motion, a projection back in time would take Betelgeuse around 290 parsecs farther from the galactic plane—an implausible hypothesis, as there is no star formation region there. Moreover, Betelgeuse's projected pathway does not appear to intersect with either the 25 Ori subassociation or the far younger Orion Nebula Cluster (ONC, also known as Ori OB1d), particularly since Very Long Baseline Array astrometry yields a distance to the ONC between 389 and 414 parsecs. Consequently, it is likely that Betelgeuse has not always had its current motion through space and has changed course at one time or another, possibly the result of a nearby stellar explosion.

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 million years ago from the [http://antwrp.gsfc.nasa.gov/apod/ap101023.html molecular clouds] observed in Orion, but has evolved rapidly due to its unusually high mass.

Like many young stars in Orion whose mass is greater than 10 M_☉, Betelgeuse will use its fuel quickly and not live very long. On the Hertzsprung-Russell diagram, Betelgeuse has moved off the main sequence and has swelled and cooled to become a red supergiant. Although young, Betelgeuse has probably exhausted the hydrogen in its core—unlike its OB cousins born about the same time—causing it to contract under the force of gravity into a hotter and denser state. As a result, it has begun to fuse helium into carbon and oxygen producing enough radiation to unfurl its outer envelopes of hydrogen and helium. Its extreme luminosity is being generated by a mass so large that the star will eventually fuse higher elements through neon, magnesium, sodium, and silicon all the way to iron, at which point it will probably collapse and explode as a type II supernova.{{cite web

| title=Betelgeuse (Alpha Orionis)

| publisher=University of Illinois

| author=Kaler, James B. (Jim)

| work=Stars website

| url=http://stars.astro.illinois.edu/sow/betelgeuse.html

| accessdate=19 July 2009}}

[[File:Star-sizes.jpg|left|thumb|300px|Relative sizes of the planets in the Solar System and several well-known stars, including Betelgeuse

1. Mercury < Mars < Venus < Earth

2. Earth < Neptune < Uranus < Saturn < Jupiter

3. Jupiter < Wolf 359 < Sun < Sirius

4. Sirius < Pollux < Arcturus < Aldebaran

5. Aldebaran < Rigel < Antares < Betelgeuse

6. Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris.]]

As an early M-type supergiant, Betelgeuse is one of the largest, most luminous and yet one of the most ethereal stars known. A radius of 5.5 AU is roughly 1,180 times the radius of the Sun—a sphere so imposing that it could contain over 2 quadrillion Earths (2.15 × 10¹⁵) or more than 1.6 billion (1.65 × 10⁹) Suns. That is the equivalent of Betelgeuse being a giant football stadium like Wembley Stadium in London with the Earth a tiny pearl, 1 millimeter in diameter, orbiting a Sun the size of a mango.For computations relating to Betelgeuse volume, click [show].

{{Collapse|1= The analogy is based on the computation of certain ratios – specifically the diameter, radius and volume of the three celestial bodies in question, Betelgeuse, the Sun and Earth. Once these ratios are derived, the relative size of each as they relate to Wembley Stadium can be easily determined. The calculations begin with the formula for angular diameter as follows:

• Betelgeuse diameter ≈ 0.0552 arcseconds × 197.0 pc ≈ 11.000 AU (rounded up) × 149,597,871 km ≈ 1.646 ×10⁹ km,
• Betelgeuse radius ≈ 11.000 AU ÷ 2 ≈ 5.500 AU × 149,597,871 km ≈ 8.230 ×10⁸ km ≈ 823,000,000 km,
• Betelgeuse volume ≈ (4÷3×π) × 823,000,000³ ≈ 2.335 × 10²⁷ km³.

Also:

• Solar radius ≈ 696,000 km. Volume ≈ 1.412×10¹⁸ km³,
• Earth radius ≈ 6,371.0 km. Volume ≈ 1.083×10¹² km³.
• Wembley Bowl Volume ≈ 1,139,100 m³. Spherical radius ≈ (1,139,100m³ ÷ (4/3*π))^1/3 ≈ 64.787 m or 64,787 mm.

Therefore:

• Betelgeuse ≈ (2.335 × 10²⁷) ÷ (1.412×10¹⁸) ≈ 1.654 × 10⁹ Suns,
• Betelgeuse ≈ (2.335 × 10²⁷) ÷ (1.083×10¹²) ≈ 2.156 × 10¹⁵ Earths.

• Solar volume relative to Wembley ≈ 1,139,100 m³ ÷ (1.654 × 10⁹) × 10⁹{i.e. to convert to mm³} ≈ 689,000 mm³ (rounded up)
• Solar diameter relative to Wembley ≈ (689,000 mm³ ÷ (4/3*π))^1/3 ≈ 55.61845 × 2 ≈ 110 mm
• Earth volume relative to Wembley ≈ 1,139,100 m³ ÷ (2.156 × 10¹⁵) × 10⁹{i.e. to convert to mm³} ≈ 0.528 mm³
• Earth diameter relative to Wembley ≈ (0.528 mm³ ÷ (4/3*π))^1/3 ≈ 0.501 × 2 ≈ 1.002 mm
• Earth's orbital radius (1 AU) relative to Wembley ≈ 1 AU ÷ 5.5 AU × 64.787 meters = 11.8 m

Conclusion:

• If the immense space of Wembley Stadium were Betelgeuse, the Earth would be a tiny pearl, 1.0 mm in diameter, orbiting a Sun, 11.0 cm in diameter (i.e. the size of an average mango or grapefruit), with an orbital distance of about 11.8 m. |bg=#F0F2F5}} Moreover, recent observations of Betelgeuse exhibiting a 15% contraction in angular diameter would equate to a shortening of the star's radius from about 5.5 to 4.6 AU, assuming that the photosphere is a perfect sphere. A reduction of this magnitude would correspond to a diminution in photospheric volume of about 41%.For computations relating to stellar contraction, click [show].{{Collapse|1=

As pointed out in the Angular anomalies section, the observed contraction could be due to a shrinking of the star's radius or by other phenomena. Assuming the photosphere is spherical, calculating a reduction in volume begins with the formula for angular diameter as follows:

Calculations for 1993 values:

• Betelgeuse radius ≈ 0.056 arcseconds × 197.0 pc ≈ 11.032 AU ÷ 2 ≈ 5.516 AU × 149,597,871 km ≈ 825,000,000 km,
• Betelgeuse volume ≈ (4÷3×π) × 825,000,000³ ≈ 2.352 × 10²⁷ km³.

Calculations for 2008 values:

• Betelgeuse radius ≈ 0.047 arcseconds × 197.0 pc ≈ 9.260 AU ÷ 2 ≈ 4.630 AU × 149,597,871 km ≈ 692,500,000 km,
• Betelgeuse volume ≈ (4÷3×π) × 692,500,000³ ≈ 1.391 × 10²⁷ km³.

Therefore:

• Betelgeuse change in volume ≈ 2.352 × 10²⁷ km³ – 1.391 × 10²⁷ km³ ≈ –9.610E × 10²⁶ km³
• Betelgeuse percent change in volume ≈ –9.610E × 10²⁶ km³ ÷ 2.352 × 10²⁷ km³ ≈ –40.86%
• Betelgeuse volume change as a function of Solar volume ≈ –9.610E × 10²⁶ ÷ 1.412×10¹⁸ km³ ≈ –681,000,000 Suns.|bg=#F0F2F5}}

File:Post L2 Play-Off Final.jpg. The center circle (9.15 m radius) is a close analogy for the Earth's orbit around the Sun, while the air in the stadium is actually far more dense than the star itself.]]

Not only is the photosphere enormous, but the star is surrounded by a complex circumstellar environment where light could take over three years just to escape. In the outer reaches of the photosphere, the density is extremely low. In volume, Betelgeuse exceeds the Sun by a factor of about 1.6 billion. Yet the actual mass of the star is believed to be no more than 20 M_☉, with mass loss estimates projected at one to two Suns since birth. Consequently, the average density of this stellar mystery is less than twelve parts-per-billion (1.119 × 10⁻⁸) that of the Sun. Such star matter is so tenuous, in fact, that Betelgeuse has often been called a "red-hot vacuum".

In the late phase of stellar evolution, massive stars like Betelgeuse exhibit high rates of mass loss, possibly as much as 1 M_☉ every 10,000 years, resulting in a complex circumstellar environment that is constantly in flux. In a recent paper, Stephen Ridgeway points out that "stellar mass loss is 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."

{{cite journal

| title=Quantifying Stellar Mass Loss with High Angular Resolution Imaging

| author=Ridgway, Stephen

| journal=Astronomy & Astrophysics

| volume=247

| year=2009

| bibcode=2009astro2010S.247R

| last2=Aufdenberg

| last3=Creech-Eakman

| last4=Elias

| last5=Howell

| last6=Hutter

| last7=Karovska

| last8=Ragland

| last9=Wishnow

| pages=247

| first2=Jason

| first3=Michelle

| first4=Nicholas

| display-authors=4

| first5=Steve

| first6=Don

| first7=Margarita

| first8=Sam

| first9=Ed|arxiv = 0902.3008 }} The physical mechanism of this mass loss, however, is not well understood. When Schwarzschild first proposed his theory of monster convection cells, he argued it was the likely cause in evolved supergiants like Betelgeuse. Recent work has corroborated this hypothesis, yet certain mysteries remain to be solved—specifically 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. Current observations in fact suggest that a star like Betelgeuse may spend a portion of its lifetime as a red supergiant, but then cross back across the H-R diagram, passing once again through a brief yellow supergiant phase and then exploding as either a blue supergiant or Wolf-Rayet star.{{cite journal

| author=Levesque, E. M.

| title=The Physical Properties of Red Supergiants

| journal=Astronomical Society of the Pacific

| year=2010

| date=June 2010

| volume=425 Hot and Cool: Bridging Gaps in Massive Star Evolution ASP Conference Series

| url=http://arxiv.org/pdf/0911.4720v1.pdf

| accessdate=3 July 2012

| bibcode = 2010ASPC..425..103L | arxiv = 0911.4720 | pages = 103 }}File:Betelgeuse Plume eso0927d.jpg showing Betelgeuse with a gigantic bubble boiling on its surface and a radiant plume of gas being ejected to at least six photospheric radii or roughly the orbit of Neptune]]

As a result of work done by Pierre Kervella and his team at the Paris observatory, astronomers may be close to solving this mystery. Kervella noticed a large plume of gas extending outward at least six times the stellar radius indicating that Betelgeuse is not shedding matter evenly in all directions. The plume's presence, in fact, 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 many times at different wavelengths. However, due to the refined capabilities of the NACO adaptive optics on the VLT, these asymmetries have come into focus. The two mechanisms that could cause such asymmetrical mass loss, Kervella noted, were large-scale convection cells or polar mass loss, possibly due to rotation. Probing deeper still with ESO's AMBER, Keiichi Ohnaka observed that the gas in the supergiant's extended atmosphere is 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.

{{cite journal

| title=Spatially Resolving the Inhomogeneous Structure of the Dynamical Atmosphere of Betelgeuse with VLTI/AMBER

| author=A. P.Ohnaka, K.

| journal=Astronomy & Astrophysics

| volume= 503 | issue=1 | pages=183–95

| year=2009

| bibcode=2009A&A...503..183O

| doi=10.1051/0004-6361/200912247

| last2=Hofmann

| first2=K.-H.

| last3=Benisty

| first3=M.

| last4=Chelli

| first4=A.

| display-authors=4

| last5=Driebe

| first5=T.

| last6=Millour

| first6=F.

| last7=Petrov

| first7=R.

| last8=Schertl

| first8=D.

| last9=Stee

| first9=Ph.

|arxiv = 0906.4792 | s2cid=17850433

}}

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.

File:ESO Paranal Platform.jpg) in Paranal, Chile]]

At about 0.45 stellar radii (~2–3 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 1500 ± 500 K.

{{cite journal

| title=Water on the Early M Supergiant Stars α Orionis and μ Cephei

| author=Tsuji, T.

| journal=The Astrophysical Journal

| volume=538 | issue=2 | pages=801–07

| year=2000

| url=http://iopscience.iop.org/0004-637X/538/2/801/pdf/51446.web.pdf

| bibcode=2000ApJ...538..801T

| doi=10.1086/309185

| s2cid=122207991

}} Water vapor had been originally detected in the supergiant's spectrum back in the 1960s with the two Stratoscope projects but had been ignored for decades. Recent studies suggest that the MOLsphere may also contain SiO and Al₂O₃—molecules which could explain the formation of dust particles.

File:Eso-paranal-16.jpg

Extending for several radii (~10–40 AU) about the photosphere there exists another cool region known as an asymmetric gaseous envelope. It is enriched in oxygen and especially in nitrogen relative to carbon. These composition anomalies are likely caused by contamination by CNO processed material from the inside of Betelgeuse.{{cite journal

| title=Carbon, Nitrogen, and Oxygen Abundances in Betelgeuse

| author=Lambert, D. L.; Brown, J. A.; Hinkle, K. H.; Johnson, H. R.

| journal=Astrophysical Journal

| volume=284

| pages=223–37

| year=1984

| bibcode=1984ApJ...284..223L

| doi=10.1086/162401

}}

The radio-telescope images taken in 1998 confirm that Betelgeuse has a dense highly complex atmosphere, with a temperature of 3,450 ± 850K—similar to that recorded on the star's surface but much lower than surrounding gas in the same region.{{cite web

|title=VLA Shows "Boiling" in Atmosphere of Betelgeuse

|publisher=National Radio Astronomy Observatory

|author=Dave Finley

|date=8 April 1998

|url=http://www.nrao.edu/pr/1998/betel/

|accessdate=7 September 2010

}}

{{cite journal

| title=Large Convection Cells as the Source of Betelgeuse's Extended Atmosphere

| author=Lim, Jeremy; Carilli, Chris L.; White, Stephen M.; Beasley, Anthony J.; Marson, Ralph G.

| journal=Nature

| volume=392

| issue=6676

| pages=575–77

| year=1998

| bibcode=1998Natur.392..575L

| doi=10.1038/33352

| s2cid=4431516

}} 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 because of gas heated to very high temperatures near its surface, it now appears that several giant convection cells propel gas from the star's surface into its atmosphere." 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.

The chromosphere, as mentioned earlier, was directly imaged by the Faint Object Camera on board the Hubble Space Telescope in the ultraviolet wavelengths. The images also revealed a bright area in the southwest quadrant of the disk. The average radius of the chromosphere in 1996 was about 2.2 times the optical disk (~10 AU) and was reported to have a temperature no higher than 5,500K. 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 197 pc, the size of the chromosphere could be up to 200 AU

{{cite journal

| title=Spatially Resolved STIS Spectroscopy of Betelgeuse's Outer Atmosphere

| author=Lobel, A.; Aufdenberg, J.; Dupree, A. K.; Kurucz, R. L.; Stefanik, R. P.; Torres, G.

| journal=Publications of the Astronomical Society of the Pacific

| page= 641

| year=2004

| bibcode=2004IAUS..219..641L

| quote=In the article, Lobel et al. equate 1 arcsecond to approximately 40 stellar radii, a calculation which in 2004 likely assumed a Hipparcos distance of 131 pc (430 ly) and a photospheric diameter of 0.0552" from Weiner et al.|arxiv = astro-ph/0312076

| last2=Aufdenberg

| last3=Dupree

| last4=Kurucz

| last5=Stefanik

| last6=Torres

| volume=219}} The observations have conclusively demonstrated that the warm chromospheric plasma spatially overlaps and coexists with cool gas in Betelgeuse's gaseous envelope as well as with the dust in its circumstellar dust shells (see below).

File:Nebula around Betelgeuse.jpg's VLT image of a complex nebula around Betelgeuse; the tiny red circle in the middle represents the photosphere, as it ejects its plume of gas into the immediate atmosphere ultimately creating a dust environment that extends ~400 AU from the star.{{cite news|title=The Flames of Betelgeuse|url=http://www.eso.org/public/news/eso1121/|accessdate=24 June 2011|newspaper=ESO Photo Release|date=23 June 2011}}{{cite web

| author=Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

| title=Stardust and Betelgeuse

| work=Today's Astronomy Picture of the Day

| date=28 June 2011

| url=http://apod.nasa.gov/apod/ap110628.html

| accessdate=10 June 2012}}]]

The first attestation of a dust shell surrounding Betelgeuse was put forth by Sutton and colleagues, who noted in 1977 that dust shells around mature stars often emit large amounts of radiation in excess of the photospheric contribution. Using heterodyne interferometry, they concluded that the red supergiant emits most of its excess beyond 12 stellar radii or roughly the distance of the Kuiper belt at 50 to 60 AU, depending on the assumed stellar radius.

{{cite journal

| title=Spatial Heterodyne Interferometry of VY Canis Majoris, Alpha Orionis, Alpha Scorpii, and R Leonis at 11 Microns

| author=Sutton, E. C.; Storey, J. W. V.; Betz, A. L.; Townes, C. H.; Spears, D. L.

| journal=Astrophysical Journal Letters

| volume=217

| pages=L97–L100

| year=1977

| doi=10.1086/182547

| bibcode=1977ApJ...217L..97S

}} Since then, there have been numerous studies done of this dust envelope at varying wavelengths yielding decidedly different results. More recent studies have estimated the inner radius of the dust shell anywhere from 0.5 to 1.0 arcseconds, or 100 to 200 AU.

{{cite journal

| title=Circumstellar Environments – V. The Asymmetric Chromosphere and Dust Shell of Alpha Orionis

| author=Skinner, C. J.

| journal=Monthly Notices of the Royal Astronomical Society

| volume=288 | issue=2 | pages=295–306

| year=1997

| bibcode=1997MNRAS.288..295S

| last2=Dougherty

| last3=Meixner

| last4=Bode

| last5=Davis

| last6=Drake

| last7=Arens

| last8=Jernigan

| first2=S. M.

| first3=M.

| first4=M. F.

| display-authors=5

| first5=R. J.

| first6=S. A.

| first7=J. F.

| first8=J. G.

| doi=10.1093/mnras/288.2.295

}}

{{cite journal

| title=Characteristics of Dust Shells around 13 Late-type Stars

| author=Danchi, W. C.; Bester, M.; Degiacomi, C. G.; Greenhill, L. J.; Townes, C. H.

| journal=The Astronomical Journal

| volume=107 | issue=4 | pages=1469–1513

| year=1994

| doi=10.1086/116960

| bibcode=1994AJ....107.1469D

}} What these studies point out is that the dust environment surrounding Betelgeuse is anything but static. In 1994, Danchi et al. reported that Betelgeuse undergoes sporadic dust production involving decades of activity followed by inactivity. A few years later, a group of astronomers led by Chris Skinner noticed significant changes in the dust shell's morphology in just one year, suggesting that the shell is asymmetrically illuminated by a stellar radiation field strongly affected by the existence of photospheric hotspots. The 1984 report of a giant asymmetric dust shell located 1 pc (206,265 AU) from the star has not been corroborated in recent studies, although another report published the same year said that three dust shells were found extending four light-years from one side of the decaying star, suggesting that, like a snake, Betelgeuse sheds its outer layers as it journeys across the heavens.

{{cite journal

| title=A Giant Asymmetric Dust Shell around Betelgeuse

| author=Baud, B.

| journal=Bulletin of the American Astronomical Society

| volume=16

| page=405

| year=1984

| date=January 1984

| bibcode=1984BAAS...16..405B

| last2=Waters

| last3=De Vries

| last4=Van Albada

| last5=Boulanger

| last6=Wesselius

| last7=Gillet

| last8=Habing

| last9=Van Der Kruit

| first2=R.

| first3=J.

| first4=G. D.

| display-authors=4

| first5=F.

| first6=P. R.

| first7=F.

| first8=H. J.

| first9=P. C.

}}

{{cite journal

| title=The Infrared Universe

| author=David, L.; Dooling, D.

| journal=Space World

| pages=4–7

| year=1984

| bibcode=1984SpWd....2....4D

| volume=2

}}

Although the exact size of the two outer CO shells remains elusive, preliminary estimates suggest that one shell extends from about 1.5 to 4.0 arcseconds with the other expanding as far as 7.0 arcseconds.{{cite journal

| title=UV, IR, and mm Studies of CO Surrounding the Red Supergiant α Orionis (M2 Iab)

| author=Harper, Graham M.

| journal=AIP Conference Proceedings

| volume= 1094

| pages=868–71

| year=2009

| doi=10.1063/1.3099254

| bibcode=2009AIPC.1094..868H

| last2=Carpenter

| first2=Kenneth G.

| last3=Ryde

| first3=Nils

| last4=Smith

| first4=Nathan

| display-authors=5

| last5=Brown

| first5=Joanna

| last6=Brown

| first6=Alexander

| last7=Hinkle

| first7=Kenneth H.

| last8=Stempels

| first8=Eric}} Using the Jovian orbit of 5.5 AU as the "average" radius for this gargantuan star, the inner shell would extend roughly 50 to 150 stellar radii (~300 to 800 AU) with the outer one as far as 250 stellar radii (~1400 AU). With the sun's heliopause estimated at about 100 AU, the size of this outer shell is almost fourteen times the size of the Solar System.

Studies since the beginning of the millennium have revealed that Betelgeuse is travelling supersonically through the interstellar medium (ISM) at a speed of 30 km per second (i.e. ~6.3 AU per year) creating a bow shock.{{cite web

|title=Akari Infrared Space Telescope: Latest Science Highlights

|publisher=European Space Agency

|url=http://www.esa.int/esaSC/SEMCJT4DHNF_index_1.html

|date=19 November 2008

|accessdate=25 June 2012}} The shock is not created by the star itself, but rather a powerful stellar wind as it ejects vast amounts of gas into the ISM at a rate of 17 km/sec, heating up the material surrounding the star thereby making it visible in infrared light. Because Betelgeuse is so bright, it was only in 1997 that the bow shock was first imaged. The cometary structure is estimated to be at least 1 parsec wide, assuming a current distance of 643 light-years.{{cite journal

| author=Noriega-Crespo, Alberto; van Buren, Dave; Cao, Yu; Dgani, Ruth

| title=A Parsec-Size Bow Shock around Betelgeuse

| journal=Astronomical Journal

| year=1997

| volume=114

| pages=837–40

| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1997AJ....114..837N&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf

| accessdate=25 June 2012

| bibcode=1997AJ....114..837N

| doi=10.1086/118517

| quote=Noriega in 1997 estimated the size to be 0.8 parsecs, having assumed the earlier distance estimate of 400ly. With a current distance estimate of 643ly, the bow shock would measure ~1.28 parsecs or over 4 ly}}

Recent 3D hydrodynamic simulations of the bow shock indicate that it is very young—less than 30,000 years old—suggesting either of two possibilities: one, that Betelgeuse moved into a region of the ISM with very different properties recently or two, that Betelgeuse itself has undergone a significant transformation as its stellar wind has changed.{{cite web

|title=This Star Lives in Exciting Times, or, How Did Betelgeuse Make that Funny Shape?

|author=Newton, Elizabeth

|publisher=Astrobites

|url=http://astrobites.com/2012/04/26/this-star-lives-in-exciting-times-or-how-did-betelgeuse-make-that-funny-shape/

|date=26 April 2012

|accessdate=25 June 2012}} In their 2012 paper, Mohamed et al. propose that this phenomenon was caused by Betelgeuse transitioning from a blue supergiant (BSG) to a red supergiant (RSG). In fact, in the late evolutionary stage of a star like Betelgeuse, evidence suggests that 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."{{cite journal

| author=Mohamed, S.; Mackey, J.; Langer, N.

| title=3D Simulations of Betelgeuse's Bow Shock

| journal=Astronomy & Astrophysics

| year=2012

| volume= 541, id.A1

| bibcode=2012A&A...541A...1M

| doi=10.1051/0004-6361/201118002

| arxiv=1109.1555v2.pdf

| pages=A1| s2cid=118435586

}}{{cite journal

| author=Mackey, Jonathan

| title=Double Bow Shocks around Young, Runaway Red Supergiants: Application to Betelgeuse

| journal=The Astrophysical Journal Letters

| year=2012

| date=May 2012

| volume=751

| issue=1, article id. L10

| pages=837–40

| bibcode=2012ApJ...751L..10M

| doi=10.1088/2041-8205/751/1/L10

| last2=Mohamed

| first2=Shazrene

| last3=Neilson

| first3=Hilding R.

| last4=Langer

| first4=Norbert

| display-authors=5

| arxiv=1204.3925v1.pdf

| last5=Meyer

| first5=Dominique M.-A.

| author6=| s2cid=118433862

}} Moreover, if future research bears out this hypothesis, Betelgeuse may well prove to have traveled close to 200,000 AU as a red supergiant scattering as much as 3 $\backslash begin\{smallmatrix\}M\_\{\backslash odot\}\; \backslash end\{smallmatrix\}$ along its trajectory.

The future fate of Betelgeuse depends on its mass—a critical factor which is not well understood. Since most investigators concede a mass greater than 10 M_☉, the most likely scenario is that the supergiant will continue to burn and fuse elements until its core is iron, at which point Betelgeuse will explode as a type II supernova. During this event the core will collapse, leaving behind a neutron star remnant some 20 km in diameter. File:Betelgeuse supernova.png's computerized depiction of Orion as it might appear from Earth should Betelgeuse explode as a supernova]] File:Chandra Gamma Ray Burst 01.jpg showing jets and supernova shell{{cite web

|title=Cosmic Forensics Confirms Gamma-ray Burst/Supernova Connection

|author=CXC/M.Weiss; Spectrum: NASA/CXC/N.Butler et al.

|publisher=Harvard-Smithsonian Center for Astrophysics

|url=http://chandra.harvard.edu/photo/2003/grb020813/

|date=Last update: 30 September 2010

|accessdate=16 November 2010}}]]

Betelgeuse is already old for its size class and is expected to explode relatively soon compared to its age. Solving the riddle of mass-loss will be the key to knowing when a supernova may occur, an event expected anytime in the next million years.{{cite journal

| author=Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

| title=Betelgeuse Resolved

| journal=Today's Astronomy Picture of the Day

| date=5 August 2009

| url=http://antwrp.gsfc.nasa.gov/apod/ap090805.html

| accessdate=17 November 2010

|quote= Betelgeuse is a candidate to undergo a spectacular supernova explosion almost anytime in the next few thousand years.}}{{cite web

|title=Betelgeuse: Will explode someday

|publisher=EarthSky Communications, Inc

|author=Sessions, Larry

|date =29 June 2009

|url=http://earthsky.org/brightest-stars/betelgeuse-will-explode-someday

|accessdate=16 November 2010}} Supporting this hypothesis are a number of unusual features that have been observed in the interstellar medium of the Orion Molecular Cloud Complex, which suggest that there have been multiple supernova explosions in the recent past.{{cite journal

| title=Optical evidence for a very large, expanding shell associated with the I Orion OB association, Barnard's loop, and the high galactic latitude H-alpha filaments in Eridanus

| author=Reynolds, R. J.; Ogden, P. M.

| journal=Astrophysical Journal

| volume= 229

| pages=942–53

| year=1979

| doi=10.1086/157028

| bibcode=1979ApJ...229..942R}} Betelgeuse's suspected birthplace in the Orion OB1 Association is the probable location for such supernovae. Since the oldest subgroup in the association has an approximate age of 12 million years, the more massive stars likely had sufficient time to reach the end of their lifespan and explode already. Also, because runaway stars are believed to be caused by supernovae, there is strong evidence that OB stars μ Columbae, AE Aurigae and 53 Arietis all originated with such explosions in Ori OB1 2.2, 2.7 and 4.9 million years ago.

At its current distance from Earth, such a supernova explosion would be the brightest recorded, outshining the Moon in the night sky and becoming easily visible in broad daylight. Professor J. Craig Wheeler of The University of Texas at Austin predicts the supernova will emit 10⁵³ ergs of neutrinos, which will pass through the star's hydrogen envelope in around an hour, then reach the Solar System several centuries later. Since its rotational axis is not pointed toward the Earth, Betelgeuse's supernova is unlikely to send a gamma ray burst in the direction of Earth large enough to damage ecosystems.{{cite web

|title=Betelgeuse

|author=Jean Tate

|publisher=Universe Today

|url=http://www.universetoday.com/42361/betelgeuse/

|date=13 Oct 2009

|accessdate=16 November 2010}} The flash of ultraviolet radiation from the explosion will likely be weaker than the ultraviolet output of the Sun. The supernova could brighten to an apparent magnitude of −12 over a two-week period, then remain at that intensity for 2 to 3 months before rapidly dimming. The year following the explosion, radioactive decay of cobalt to iron will dominate emission from the supernova remnant, and the resulting gamma rays will be blocked by the expanding envelope of hydrogen. If the neutron star remnant becomes a pulsar, then it could produce gamma rays for thousands of years.{{cite book

| title=Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe

| author=Wheeler, J. Craig

| publisher=Cambridge University Press

| location=Cambridge, UK

| year=2007

| edition=2nd

| isbn=978-0-521-85714-7

| pages=115–17}}

Due to misunderstandings caused by the 2009 publication of the star's 15% contraction, Betelgeuse has frequently been the subject of scare stories and rumors suggesting that it will explode within a year, leading to exaggerated claims about the consequences of such an event.{{cite news

| 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

| title=Tatooine's twin suns - coming to a planet near you just as soon as Betelgeuse explodes

| last=Connelly

| first=Claire

| work=News.com.au

| year=2011

| date=19 January 2011

| accessdate=2012-09-14

}}{{cite web

| url=http://blogs.discovermagazine.com/badastronomy/2010/06/01/is-betelgeuse-about-to-blow/

| title=Is Betelgeuse about to blow?

| last=Plait

| first=Phil

| year=2010

| date=1 June 2010

| accessdate=2012-09-14

| work=Bad Astronomy

| publisher=Discovery

}} The timing and prevalence of these rumors have been linked to broader misconceptions of astronomy, particularly in reference to doomsday predictions relating to the Mayan calendar.

{{cite news

| url=http://news.discovery.com/space/dont-panic-betelgeuse-wont-explode-in-2012.html

| title=Don't panic! Betelgeuse won't explode in 2012!

| last=O'Neill

| first=Ian

| year=2011

| date=20 January 2011

| accessdate=2012-09-14

| work=Discovery space news

}}

{{cite web

| url=http://blogs.discovermagazine.com/badastronomy/2011/01/21/betelgeuse-and-2012/

| title=Betelgeuse and 2012

| last=Plait

| first=Phil

| year=2011

| date=21 January 2011

| accessdate=2012-09-14

| work=Bad Astronomy

| publisher=Discovery

}} In their 2012 study, the Space Sciences Laboratory physicists point out that the apparent contraction in the star's diameter may actually be due to the complex dynamics in the star's surrounding nebula and not the star itself, reconfirming the fact that until we really understand the nature of mass loss, predicting the timing of a supernova will remain a mystery.

In 1985, Margarita Karovska, in conjunction with other astrophysicists at the CfA, announced the discovery of two close companions orbiting Betelgeuse. Analysis of polarization data from 1968 through 1983 indicated a close companion with a periodic orbit of about 2.1 years. Using speckle interferometry, the team concluded that the closer of the two companions was located at 0.06 ± 0.01" (~9 AU) from the main star with a position angle (PA) of 273 degrees, an orbit that would potentially place it within the star's chromosphere. The more distant companion was estimated at 0.51 ± 0.01" (~77 AU) with a PA of 278 degrees.{{cite journal

| title=On a Possible Close Companion to α Ori

| author=Karovska, M.; Noyes, R. W.; Roddier, F.; Nisenson, P.; Stachnik, R. V.

| journal=Bulletin of the American Astronomical Society

| volume=17

| page=598

| year=1985

| bibcode=1985BAAS...17..598K

| last2=Noyes

| last3=Roddier

| last4=Nisenson

| last5=Stachnik

}}{{cite journal

| title=On the alpha Orionis triple system

| author=Karovska, M.; Nisenson, P.; Noyes, R.

| journal=Astrophysical Journal

| volume=308

| pages=675–85

| year=1986

| doi=10.1086/164497

| bibcode=1986ApJ...308..260K

}}

In the years that followed no confirmation of Karovska's discovery was published. In 1992, a team of collaborators from the Cavendish Astrophysics Group questioned the finding. They published a paper noting that the brightness features on the surface of Betelgeuse appear to be "too bright to be associated with a passage of the suggested companions in front of the red giant." They also noticed that these features were fainter at 710 nanometers compared to 700 by a factor of 1.8, indicating that such features would have to reside within the molecular atmosphere of the star.{{cite journal

| title=High-resolution imaging of Betelgeuse and Mira

| author=Wilson, R. W.; Baldwin, J. E.; Buscher, D. F.; Warner, P. J.

| journal=Monthly Notices of the Royal Astronomical Society

| volume=257

| issue=3

| pages=369–76

| year=1992

| bibcode=1992MNRAS.257..369W

| last2=Baldwin

| last3=Buscher

| last4=Warner

| doi=10.1093/mnras/257.3.369

}} Despite this, that same year Karovska published a new paper reconfirming her team's exegesis, but also noting that there was a meaningful correlation between the calculated position angles of the orbiting companion and the reported asymmetries, suggesting a possible connection between the two.

{{cite journal

| title=Imaging of the Surface of α ORI

| author=Karovska, M.

| journal=Proceedings of the 7th Cambridge Workshop, ASP Conference Series

| volume=26

| page=279

| year=1992

| bibcode=1992ASPC...26..279K

}} Since then, researchers have turned their attention to analyzing the intricate dynamics of the star's extended atmosphere and little else has been published on the possibility of orbiting companions, although as Xavier Haubois and his team reiterate in 2009, the possibility of a close companion contributing to the overall flux has never been fully ruled out. Dommanget's double star catalog (CCDM) lists at least four adjacent stars, all within three arcminutes of this stellar giant, yet aside from apparent magnitudes and position angles, little else is known.{{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 |accessdate=22 August 2010}} As the decade unfolds and new technologies are brought to unraveling the star's enigmatic past, conclusive evidence will likely emerge of any potential star system. Given the planned capabilities of the upcoming Gaia mission, a confirmation could occur any time after the mission's scheduled launch in August 2013.{{cite web

|title=ESA space operations and situational awareness

|publisher=European Space Agency

|url=http://www.esa.int/SPECIALS/Operations/SEMK5HZTIVE_0.html

|date=Last update: 22 April 2010

|accessdate=15 November 2010}}

Betelgeuse has been known variously as Betelgeux,{{Cite encyclopedia

| title=Betelgeuse

| encyclopedia=Oxford English Dictionary

| editor=Simpson, J.; Weiner, E. (eds)

| year=1989

| edition= 2nd

| page=130

| location=Oxford

| publisher=Clarendon Press

| isbn= 0-19-861186-2}} and BeteigeuzeLikely the result of mistaking the l for an i. Ultimately, this led to the modern Betelgeuse. in German (according to BodeBode, Johann Elert, (ed.). (1782) Vorstellung der Gestirne: auf XXXIV Kupfertafeln nach der Parisier Ausgabe des Flamsteadschen Himmelsatlas, Gottlieb August Lange, Berlin / Stralsund, pl. XXIV.Bode, Johann Elert, (ed.) (1801). Uranographia: sive Astrorum Descriptio, Fridericus de Harn, Berlin, pl. XII.). Betelgeux and Betelgeuze were used until the early 20th century, when the spelling Betelgeuse became universal.{{cite book

|author=Schaaf, Fred

|year=2008

|title=The Brightest Stars

|chapter=Betelgeuse

|pages=174–82

|publisher=Wiley

|location=Hoboken, New Jersey

|isbn=978-0-471-70410-2}} There is no consensus for the correct pronunciation of the name,{{cite web|work=The Constellations Web Page|title= Alpha Orionis (Betelgeuse ) |author=Dibon-Smith, Richard|url=http://www.dibonsmith.com/ori_a.htm|accessdate=23 January 2010}} and pronunciations for the star are as varied as its spellings:

• {{IPAc-en|ˈ|b|ɛ|t|əl|dʒ|uː|z}} Oxford English Dictionary and Royal Astronomical Society of Canada
• {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|z}} Oxford English Dictionary
• {{IPAc-en|ˈ|b|ɛ|t|əl|dʒ|ə|z}} (The Friendly Stars){{cite web

| title=SpaceWatch – A Star by Any Other Name

| author=Kanipe, Jeff

| website=Space.com

| date=30 June 2005

| url=http://www.space.com/spacewatch/spacewatch_001214.html

| accessdate=23 October 2009

| archiveurl = http://web.archive.org/web/20090522195511/http://www.space.com/spacewatch/spacewatch_001214.html

| archivedate = 2009-05-22}}

• {{IPAc-en|ˈ|b|iː|t|əl|dʒ|uː|s}} (Canadian Oxford Dictionary, Webster's Collegiate Dictionary)

There is some uncertainty surrounding the first element of the name, rendered as "Bet-". However, "abet" or {{lang|ar|إبط}} is the Arabic word for "armpit",{{cite journal | last=Davis | first=George R., Jr. | title=The pronunciations, derivations, and meanings of a selected list of star names | journal=Popular Astronomy | volume=52 | pages=8–29 | year=1944 | bibcode=1944PA.....52....8D }} See p. 23. which is where the star is located in the Orion constellation. Betelgeuse is often mistranslated as "armpit of the central one".{{cite book | first=Ian | last=Ridpath | year=2006 | authorlink=Ian Ridpath | page=8 | title=The Monthly Sky Guide | edition=7th | publisher=Cambridge University Press | isbn=0-521-68435-8 | url=https://books.google.com/books?id=P3JhtnAX-PwC&pg=PA8 }} In his 1899 work Star-Names and Their Meanings, American amateur naturalist Richard Hinckley Allen stated the derivation was from the {{lang|ar|ابط الجوزاء}} {{transl|ar|Ibṭ al-Jauzah}}, which he claimed degenerated into a number of forms including Bed Elgueze, Beit Algueze, Bet El-gueze, Beteigeuze and more, to the (then) current forms Betelgeuse, Betelguese, Betelgueze and Betelgeux. The star was named Beldengeuze in the Alfonsine Tables,{{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|doi=10.1177/002182868601700202 |url=http://adsabs.harvard.edu/full/1986JHA....17...89K|bibcode = 1986JHA....17...89K |s2cid=118597258 }} and Italian Jesuit priest and astronomer Giovanni Battista Riccioli had called it Bectelgeuze or Bedalgeuze.{{cite book

| author=Allen, Richard Hinckley

| year=1963 |origyear=1899

| title=Star Names: Their Lore and Meaning

| edition=rep.

| publisher=Dover Publications Inc.

| location=New York, NY

| url= http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Orion*.html

| isbn=0-486-21079-0

| pages = 310–12}} 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}} {{transl|ar|Yad al-Jauzā'}} meaning "the Hand of al-Jauzā'", i.e., Orion.{{cite book

|author=Kunitzsch, Paul

|year=1959

|title=Arabische Sternnamen in Europa

|publisher=Otto Harrassowitz

|location=Wiesbaden

|page=}}

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}} {{transl|ar|Bait al-Jauzā'}} ("house of Orion") or {{lang|ar|بط الجوزاء}} {{transl|ar|Baţ al-Jauzā'}}, incorrectly thought to mean "armpit of Orion" (a true translation of "armpit" would be {{lang|ar|ابط}}, transliterated as {{transl|ar|Ibţ}}). This led to the modern rendering as Betelgeuse.{{cite book

|author= Kunitzsch, Paul; Smart, 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 Pub

|location = Cambridge, MA

|isbn = 978-1-931559-44-7

|page = 45}}

Other writers have since accepted Kunitzsch's explanation.

The last part of the name, "-elgeuse", comes from the Arabic {{lang|ar|الجوزاء}} {{transl|ar|al-Jauzā'}}, a historical Arabic name of the constellation Orion, a feminine name in old Arabian legend, and of uncertain meaning. Because {{lang|ar|جوز}} {{transl|ar|j-w-z}}, the root of {{transl|ar|jauzā'}}, means "middle", {{transl|ar|al-Jauzā'}} roughly means "the Central One". Later, {{transl|ar|al-Jauzā'}} was also designated as the scientific Arabic name for Orion and for Gemini. The current Arabic name for Orion is {{lang|ar|الجبار}} {{transl|ar|al-Jabbār}} ("the Giant"), although the use of {{lang|ar|الجوزاء}} {{transl|ar|al-Jauzā'}} in the name of the star has continued. The 17th century English translator Edmund Chilmead gave it the name Ied Algeuze ("Orion's Hand"), from Christmannus. Other Arabic names recorded include {{transl|ar|Al Yad al Yamnā}} ("the Right Hand"), {{transl|ar|Al Dhira}} ("the Arm"), and {{transl|ar|Al Mankib}} ("the Shoulder"), all appended to "of the giant", as {{lang|ar|منكب الجوزاء}} {{transl|ar|Mankib al Jauzā'}}. In Persian, however, the name is {{lang|fa|اِبطالجوزا}}, derived from the Arabic {{lang|ar|ابط الجوزاء}} {{transl|ar|Ibţ al-Jauzā'}}, "armpit of Orion".File:Dunhuang Star Atlas - Orion.jpg, circa AD 700, showing {{lang|zh|参宿四}} {{lang|zh-Latn|Shēnxiùsì}} (Betelgeuse), the Fourth Star of the constellation of Three Stars{{cite web

| title=Dunhuang Star Chart

| publisher=British Library

| work=International Dunhuang Project (IDP)

| url=http://idp.bl.uk/4DCGI/education/astronomy/atlas.html

| accessdate=16 June 2012}}]]

Other terms for Betelgeuse included the Persian {{lang|fa-Latn|Bašn}} "the Arm", and Coptic {{lang|cop-Latn|Klaria}} "an Armlet". {{lang|sa-Latn|Bahu}} was its Sanskrit name, as part of a Hindu understanding of the constellation as a running antelope or stag. In traditional Chinese astronomy, Betelgeuse was known as {{lang|zh|参宿四}} ({{lang|zh-Latn|Shēnxiùsì}}, the Fourth Star of the constellation of Three Stars){{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0605/ap060525.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 25 日] as the Chinese constellation {{lang|zh|参宿}} originally referred to the three stars in the girdle of Orion. This constellation was ultimately expanded to ten stars, but the earlier name stuck.{{cite web |url = http://www.ianridpath.com/startales/orion2.htm |last = Ridpath |first = Ian |title = Orion Continued |accessdate = 24 June 2012 |work = Star Tales}} In Japan, this star was called Heike-boshi, ({{lang|ja|平家星}}), and alludes to a legendary war in Japanese history between two powerful families, the Taira or Heike clan, who had adopted Betelgeuse and its red color as its symbol, and the Minamoto or Genji clan who chose the white star Rigel.{{cite web

|title=Yowatashi Boshi; Stars that Pass in the Night

|author=Steve Renshaw and Saori Ihara

|publisher=Griffith Observer

|url=http://www2.gol.com/users/stever/orion.htm

|date=October 1999

|accessdate=25 June 2012}}Hōei Nojiri"Shin seiza jyunrei"p.19 {{ISBN|978-4-12-204128-8}}

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".{{cite journal|last=Henry|first=Teuira |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}} A Hawaiian term for it was Kaulua-koko "brilliant red star".{{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&dq=Betelgeuse+Chinese+astronomy&pg=PA46}} The Lacandon people of Central America knew it as chäk tulix "red butterfly".{{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|pages=39|isbn=0292752261|url=https://books.google.com/books?id=DgqLplWtGPgC&dq=betelgeuse+folklore&pg=PA39}}

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 Roman war god, has been closely associated with the martial archetype of conquest for millennia, and by extension, the motif of death and rebirth. 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 made of ivory made for him, with Betelgeuse as the shoulder, its color reminiscent of the reddish yellow sheen of ivory.

In the Americas, Betelgeuse signifies a severed limb of a man-figure (Orion)—the Taulipang of Brazil know the constellation as Zililkawai, a hero whose leg was cut off by his wife, with the variable light from 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.{{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}}

A Sanskrit name for Betelgeuse was ãrdrã "the moist one", eponymous of the Ardra lunar mansion in Hindu astrology.{{cite book|last=Motz|first=Lloyd|coauthors=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=1-85410-088-2}} It was linked via Orion's association with stormy weather to the Rigvedic God of storms Rudra. The constellations in Macedonian folklore represented agricultural items and animals, reflecting their village 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 a.m. in late summer and autumn signified the time for villager menfolk to go to the fields and plough.{{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}} In South African mythology, Betelgeuse was perceived as a lion casting a predatory gaze toward the three zebras represented by Orion's belt.{{cite book

| first=C. Scott | last=Littleton | year=2005 | page=1056

| title=Gods, goddesses, and mythology | volume=1

| publisher=Marshall Cavendish | isbn=0-7614-7559-1

| url=https://books.google.com/books?id=HC93q4gsOAwC&pg=PA1056 }}

The opposed locations of Orion and Scorpio, with their corresponding bright variable red stars Betelgeuse and Antares, were noted by ancient cultures around the world. The setting of Orion and rising of Scorpio signify the death of Orion by the scorpion. In China they signify brothers and rivals Shen and Shang. The 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 significant, with their corresponding constellations seen as a pair of scorpions. Scorpion days marked as nights that both constellations could be seen.{{cite book|last=Kelley, David H.; Milone, Eugene F.; Aveni, A.F. |title=Exploring Ancient Skies: A Survey of Ancient and Cultural Astronomy|publisher=Springer|location=New York, New York|year=2011|pages=307|isbn=978-1441976239|url=https://books.google.com/books?id=ILBuYcGASxcC&q=Betelgeuse+&pg=PA307}}

{{seealso|Betelgeuse in fiction}}

The star's unusual name inspired the 1988 film Beetlejuice, and script writer Michael McDowell was impressed at how many people made the connection. He added that they had received a suggestion the sequel be named Sanduleak-69 202 after the former star of SN 1987A. The correspondence between the star's mythological motif of death and rebirth, the fact that Betelgeuse is believed to be a dying star and the film's theme of ghosts haunting the living is particularly poignant, especially in light of Carl Jung's theory of synchronicity. In August Derleth's short story "The Dweller in the Darkness" set in H. P. Lovecraft's Cthulhu Mythos, Betelgeuse is the home of the 'benign' Elder Gods. There has been much debate over the identity of the red star Borgil mentioned in Lord of the Rings, with Aldebaran, Betelgeuse and even the planet Mars touted as candidates. Professor Kristine Larsen has concluded the evidence points to it being Aldebaran as it precedes Menelvagor (Orion).{{cite journal

|author=Larsen, Kristine

|title=A Definitive Identification of Tolkien's "Borgil": An Astronomical and Literary Approach

|journal=Tolkien Studies

|volume=2

|year=2005

|issue=1

|pages=161–70

|doi=10.1353/tks.2005.0023|s2cid=170378050

}} Astronomy writer Robert Burnham, Jr. proposed the term padparadaschah which denotes a rare orange sapphire in India, for the star. In the popular science fiction series "The Hitchhiker's Guide to the Galaxy" by Douglas Adams, Ford Prefect was from "a small planet somewhere in the vicinity of Betelgeuse."{{cite book

|title=Magic Words: A Dictionary

|author=Conley, Craig

|year=2008

|page=121

|url=https://books.google.com/books?id=3SB60Wavy6MC&dq=%22Ford+Prefect%22+Betelgeuse&pg=PA121

|accessdate=22 September 2010

|isbn=978-1-57863-434-7

|publisher=Weiser}} In the poetic work "Betelguese, a trip through hell" by Jean Louis De Esque, hell is located on Betelguese because De Esque believed that it was "a celestial pariah, an outcast, the largest of all known comets or outlawed suns in the universe."{{cite wikisource |title=Betelguese, a trip through hell |wslink=Betelguese, a trip through hell |last=De Esque |first=Jean Louis |year=1908 |publisher=Connoisseur's Press |pages=7}}

There have been two American navy ships named after the star, both World War II vessels, the {{USS|Betelgeuse|AKA-11}} launched in 1939 and {{USS|Betelgeuse|AK-260}} launched in 1944. In 1979, a French supertanker named Betelgeuse was moored off Whiddy Island discharging oil when it exploded, killing 50 people in one of the worst disasters in Ireland's history.{{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

| accessdate=10 June 2011}}

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{{Reflist|colwidth=25em}}

{{commons category|Betelgeuse}}

• [http://www.mrao.cam.ac.uk/telescopes/coast/betel.html Surface imaging of Betelgeuse with COAST and the WHT] Interferometric images taken at different wavelengths.
• [http://www.ipac.caltech.edu/outreach/Edu/Regions/irregions.html Near, Mid and Far Infrared] Infrared Processing and Analysis Center (IPAC) webpage showing pictures at various wavelengths.
• APOD Pictures:

1. [http://apod.nasa.gov/apod/ap071225.html Mars and Orion Over Monument Valley] Skyscape showing the relative brightness of Betelgeuse and Rigel.
2. [http://apod.nasa.gov/apod/ap101023.html Orion: Head to Toe] Breathtaking vista the Orion Molecular Cloud Complex from Rogelio Bernal Andreo.
3. [http://apod.nasa.gov/apod/ap100106.html The Spotty Surface of Betelgeuse] A reconstructed image showing two hotspots, possibly convection cells.
4. [http://apod.nasa.gov/apod/ap001222.html Simulated Supergiant Star] Freytag's "Star in a Box" illustrating the nature of Betelgeuse's "monster granules".
5. [http://apod.nasa.gov/apod/ap000725.html Why Stars Twinkle] Image of Betelgeuse showing the effect of atmospheric twinkling in a microscope.

• [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}}

{{Good article}}

Orionis, Alpha

Orionis, 58

039801

027989

2061

Category:Orion (constellation)

Category:M-type supergiants

Category:Semiregular variable stars

Category:Arabic words and phrases

Category:Stars with proper names

{{Link FA|it}}

ar:منكب الجوزاء

az:Bətəlgeyze

bn:আর্দ্রা

be:Бетэльгейзе

bg:Бетелгейзе

bs:Betelgez

ca:Betelgeuse

cs:Betelgeuze

da:Betelgeuse

de:Beteigeuze

el:Μπετελγκέζ

es:Betelgeuse

eo:Betelĝuzo

eu:Alfa Orionis

fa:ابط‌الجوزا

fr:Bételgeuse

ga:Betelgeuse

gl:Alpha Orionis

ko:베텔게우스

hi:आर्द्रा तारा

hr:Betelgeuse

io:Betelgeuse

id:Betelgeuse

is:Betelgás

it:Betelgeuse

he:ביטלג'וז

ka:ბეთელჰეიზე

ku:Betelcewza

la:Alpha Orionis

lv:Betelgeize

lb:Betelgeuse (Stär)

lt:Betelgeizė

li:Betelgeuse

hu:Betelgeuse

mk:Бетелгез

ml:തിരുവാതിര (നക്ഷത്രം)

mr:काक्षी

ms:Betelgeuse

nl:Betelgeuze (ster)

ja:ベテルギウス

no:Betelgeuse

nds:Beteigeuze

pl:Betelgeza

pt:Betelgeuse

ro:Betelgeuse

ru:Бетельгейзе

simple:Betelgeuse

sk:Betelgeuze

sr:Бетелгез

sh:Betelgeuse

fi:Betelgeuze

sv:Betelgeuse

ta:திருவாதிரை (நட்சத்திரம்)

tt:Бителҗәүза

th:ดาวบีเทลจุส

tr:Betelgeuse

uk:Бетельгейзе

vi:Betelgeuse

vls:Betelgeuze

zh:參宿四