Difference between revisions of "Betelgeuse" - New World Encyclopedia

From New World Encyclopedia
(Checked spelling and applied Ready tag.)
(19 intermediate revisions by 5 users not shown)
Line 1: Line 1:
{{Ready}}
+
{{Ready}}{{Images OK}}{{Approved}}{{Copyedited}}
 
:''This article is about the star.''
 
:''This article is about the star.''
 
{{Starbox begin
 
{{Starbox begin
Line 11: Line 11:
 
| epoch = [[J2000.0]]
 
| epoch = [[J2000.0]]
 
| constell = [[Orion (constellation)|Orion]]
 
| constell = [[Orion (constellation)|Orion]]
| ra = {{RA|05|55|10.3053}}<ref name="SIMBAD">[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=betelgeuse SIMBAD query result: V* alf Ori—Semi-regular pulsating Star.] Centre de Données astronomiques de Strasbourg. Retrieved November 11, 2008.</ref>
+
| ra = {{RA|05|55|10.3053}}<ref name="SIMBAD">[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=betelgeuse SIMBAD query result: V* alf Ori—Semi-regular pulsating Star.] ''Centre de Données astronomiques de Strasbourg''. Retrieved November 11, 2008.</ref>
 
| dec = {{DEC|+07|24|25.426}}<ref name="SIMBAD" />
 
| dec = {{DEC|+07|24|25.426}}<ref name="SIMBAD" />
 
| appmag_v = 0.58<ref name="SIMBAD" /> (0.3&nbsp;to&nbsp;1.2)
 
| appmag_v = 0.58<ref name="SIMBAD" /> (0.3&nbsp;to&nbsp;1.2)
Line 23: Line 23:
 
{{Starbox astrometry
 
{{Starbox astrometry
 
| radial_v = +21.0<ref name="SIMBAD" />
 
| radial_v = +21.0<ref name="SIMBAD" />
| prop_mo_ra = 24.95 ± 0.08<ref name=harper2008 />
+
| prop_mo_ra = 24.95 ± 0.08<ref name=harper2008>Graham M. Harper, Alexander Brown, and Edward F. Guinan. 2008. [http://adsabs.harvard.edu/abs/2008AJ....135.1430H A New VLA-''Hipparcos'' Distance to Betelgeuse and its Implications.] ''The Astronomical Journal'' 135(4):1430-1440. (5), Table 6. Retrieved November 11, 2008.</ref>
 
| prop_mo_dec = 9.56 ± 0.15<ref name=harper2008 />
 
| prop_mo_dec = 9.56 ± 0.15<ref name=harper2008 />
 
| parallax = 5.07
 
| parallax = 5.07
Line 35: Line 35:
 
| mass = 20<ref name=uiuc />
 
| mass = 20<ref name=uiuc />
 
| radius = 950-1000<ref name=uiuc />
 
| radius = 950-1000<ref name=uiuc />
| rotation = 17&nbsp;years (14.6&nbsp;km/s)<ref name="uitenbroek_1998">Uitenbroek, H., A.K. Dupree, and R.L. Gilliland. 1998. [http://www.iop.org/EJ/article/1538-3881/116/5/2501/980184.html Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of &alpha; Orionis.] ''The Astronomical Journal.'' 116:2501–2512. Retrieved November 11, 2008.</ref>
+
| rotation = 17&nbsp;years (14.6&nbsp;km/s)<ref name="uitenbroek_1998">H. Uitenbroek, A.K. Dupree, and R.L. Gilliland. 1998. [http://www.iop.org/EJ/article/1538-3881/116/5/2501/980184.html Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of &alpha; Orionis.] ''The Astronomical Journal'' 116:2501–2512. Retrieved November 11, 2008.</ref>
 
| luminosity = 135,000<ref name=uiuc />
 
| luminosity = 135,000<ref name=uiuc />
| temperature=3,500<ref name="apj545">Lobel, A., and A.K. Dupree. 2000. [http://www.journals.uchicago.edu/doi/full/10.1086/317784 Modeling the Variable Chromosphere of &alpha; Orionis.] ''The Astrophysical Journal.'' 545:454–474. Retrieved November 11, 2008.</ref>
+
| temperature=3,500<ref name="apj545">A. Lobel, and A.K. Dupree. 2000. [http://www.journals.uchicago.edu/doi/full/10.1086/317784 Modeling the Variable Chromosphere of &alpha; Orionis.] ''The Astrophysical Journal'' 545:454–474. Retrieved November 11, 2008.</ref>
 
| gravity=-0.5<ref name="apj545" />
 
| gravity=-0.5<ref name="apj545" />
 
}}
 
}}
Line 44: Line 44:
 
}}
 
}}
 
{{Starbox end}}
 
{{Starbox end}}
'''Betelgeuse''' ({{pronEng|ˈbiːtəldʒuːz}} or {{IPA|/ˈbɛtəldʒuːz/}}) ( α Ori, α Orionis, [[alpha (letter)|Alpha]] Orionis) is a [[semiregular variable star]] located approximately 600 [[light-year]]s away from Earth.<ref name="SIMBAD" /><ref name=harper2008>Harper, Graham M., Alexander Brown, and Edward F. Guinan. 2008. [http://adsabs.harvard.edu/abs/2008AJ....135.1430H A New VLA-''Hipparcos'' Distance to Betelgeuse and its Implications.] ''The Astronomical Journal'' 135(4):1430-1440. (5), Table 6. Retrieved November 11, 2008.</ref> It is the second brightest [[star]] in the [[constellation]] [[Orion (constellation)|Orion]] and the ninth [[list of brightest stars|brightest star]] in the night sky. Although Betelgeuse has the [[Bayer designation]] ''alpha'', [[Rigel]] (Beta Orionis) is usually brighter (Betelgeuse is a variable star and is on occasion brighter than Rigel). The star is a [[Vertex (geometry)|vertex]] of the [[Winter Triangle]] [[Asterism (astronomy)|asterism]]. Astronomers believe Betelgeuse is only a few million years old but has evolved rapidly because of its huge size.<ref>[http://www.solstation.com/x-objects/betelgeuse.htm Betelgeuse.] SolStation. Retrieved November 11, 2008.</ref>
 
  
Betelgeuse is a [[red supergiant]] and relatively luminous and one of the [[List of largest known stars|largest stars]] known. For comparison, if the star were at the center of our [[solar system]] its surface might extend out to between the orbits of [[Mars]] and [[Jupiter]], wholly engulfing [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]] and [[Mars (planet)|Mars]]. The [[angular diameter]] of Betelgeuse was first measured in 1920&ndash;1921 by [[Albert Abraham Michelson|Michelson]] and [[Francis G. Pease|Pease]] using an [[astronomical interferometer]] on the [[Mount Wilson Observatory|Mount Wilson]] 100 [[inch]] [[telescope]].
+
'''Betelgeuse''' (also called '''[[alpha (letter)|Alpha]] Orionis''', '''α Orionis''', or '''α Ori''') is one of the brightest and largest known stars, though it is not one of the most massive. Located approximately 600 [[light-year]]s from Earth, it is part of the constellation [[Orion (constellation)|Orion]] and  a [[Vertex (geometry)|vertex]] of the [[Winter Triangle]] [[Asterism (astronomy)|asterism]]. Its large volume suggests that if it were at the center of the [[Solar System]], it would wholly engulf [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], and [[Mars (planet)|Mars]], with its surface extending out to between the orbits of [[Mars]] and [[Jupiter]]. It is classified as a [[red supergiant]] and as a [[semiregular variable star]]—that is, it shows considerable periodicity as its light changes, but this periodicity is sometimes irregular.
 +
{{toc}}
 +
==Etymology==
 +
The name Betelgeuse is a corruption of the [[Arabic language|Arabic]] ''{{lang|ar-Latn|yad al-jawzā}}'' ({{lang|ar|يد الجوزاء}}), meaning "hand of the central one." The Arabs had earlier called [[Gemini (constellation)|Gemini]] ''{{lang|ar-Latn|Jauza}}'' ("the central one") but later switched this name to Orion.
  
==Etymology==
+
European mistransliteration into [[Latin]] during the [[Middle Ages]] led to the first character ''y'' ('''ﻴ''', with two dots underneath) being misread as a ''b'' ('''ﺒ''', with only one dot underneath). Thus throughout the [[Renaissance]], the star's name was written as ''{{lang|ar-Latn|Bait al-Jauza}}'' and thought to mean ''armpit of the central one'' in Arabic. This led to the modern rendering as ''Betelgeuse'' (although a true translation of "armpit" would be {{lang|ar|ابط}}, transliterated as ''{{lang|ar-Latn|Ibţ}}'',<ref>Paul Kunitzsch and Tim Smart. 2006. ''A Dictionary of Modern Star Names.'' (Cambridge, MA: Sky Publishing. ISBN 9781931559447), 45.</ref> hence in 1899 [[Richard Hinckley Allen]] mistakenly gave the origin as ''{{lang|ar-Latn|Ibţ al Jauzah}}'').<ref name="hinkley63">Richard Hinckley Allen, 1963. ''Star Names: Their Lore and Meaning.'' (New York, NY: Dover Publications. ISBN 0486210790).</ref> In [[German language|German]], the star's name was corrupted even further: it is called ''Bete'''i'''geuze,'' because the letter '''l''' in the Romanized name was mistaken for the letter '''i'''.
The name is a corruption of the [[Arabic language|Arabic]] {{lang|ar|يد الجوزاء}} ''{{lang|ar-Latn|yad al-jawzā}}'', ''hand of the central one''. The Arabs had earlier called [[Gemini (constellation)|Gemini]] ''{{lang|ar-Latn|Jauza}}'' ("the central one") but later switched this name to Orion instead. European mistransliteration into [[Latin]] during the [[Middle Ages]] led to the first character ''y'' ('''ﻴ''', with two dots underneath) being misread as a ''b'' ('''ﺒ''', with only one dot underneath). Thus throughout the [[Renaissance]] the star's name was written as ''{{lang|ar-Latn|Bait al-Jauza}}'' and thought to mean ''armpit of the central one'' in Arabic. This led to the modern rendering as ''Betelgeuse'' (although a true translation of "armpit" would be {{lang|ar|ابط}}, transliterated as ''{{lang|ar-Latn|Ibţ}}'',<ref>Kunitzsch, Paul, and Tim Smart. 2006. ''A Dictionary of Modern Star Names.'' Cambridge, MA: Sky Publishing. ISBN 9781931559447. page 45.</ref> hence in 1899 [[Richard Hinckley Allen]] mistakenly gave the origin as ''{{lang|ar-Latn|Ibţ al Jauzah}}'').<ref name="hinkley63">Allen, Richard Hinckley. 1963. ''Star Names: Their Lore and Meaning.'' New York, NY: Dover Publications. ISBN 0486210790.</ref> In [[German language|German]], the star's name was corrupted even further: it is called ''Bete'''i'''geuze'', because the letter '''l''' in the Romanized name was mistaken for the letter '''i'''.
+
 
 +
== Variety of names ==
  
Because of its rich reddish color the star has also been called "the [[military|martial]] one" and in [[astrology]] Betelgeuse portends military or civic honors. This bright star has had many other names:
+
Betelgeuse has been called by many other names. Some examples are:
 
* ''{{lang|ar-Latn|Al Dhira}}'' (the ''Arm'')<ref name="hinkley63" />
 
* ''{{lang|ar-Latn|Al Dhira}}'' (the ''Arm'')<ref name="hinkley63" />
* ''{{lang|ar-Latn|Al Mankib}}'' (the ''Shoulder''),<ref name="hinkley63" />
+
* ''{{lang|ar-Latn|Al Mankib}}'' (the ''Shoulder'')<ref name="hinkley63" />
* ''{{lang|ar-Latn|Al Yad al Yamma}}'' (the ''Right Hand''),<ref name="hinkley63" />
+
* ''{{lang|ar-Latn|Al Yad al Yamma}}'' (the ''Right Hand'')<ref name="hinkley63" />
* ''{{lang|hi-Latn|Ardra}}'' ([[Hindi]],<ref name="hinkley63" /> and name of [[Hindu]] [[Nakshatra]]),
+
* ''{{lang|hi-Latn|Ardra}}'' ([[Hindi]],<ref name="hinkley63" /> and name of [[Hindu]] [[Nakshatra]])
* ''{{lang|sa-Latn|Bahu}}'' ([[Sanskrit]]),<ref name="hinkley63" />
+
* ''{{lang|sa-Latn|Bahu}}'' ([[Sanskrit]])<ref name="hinkley63" />
 
* ''{{lang|fa-Latn|Bašn}}'' ([[Persian language|Persian]]) (the ''Arm''),
 
* ''{{lang|fa-Latn|Bašn}}'' ([[Persian language|Persian]]) (the ''Arm''),
* ''{{lang|sux-Latn|Gula}}'' ([[Euphrates|Euphratean]]),
+
* ''{{lang|sux-Latn|Gula}}'' ([[Euphrates|Euphratean]])
* ''Ied Algeuze'' (''Orion's Hand''),<ref name="hinkley63" />
+
* ''Ied Algeuze'' (''Orion's Hand'')<ref name="hinkley63" />
 
* ''{{lang|cop-Latn|Klaria}}'' ([[Coptic language|Coptic]]) (an ''Armlet'')<ref name="hinkley63" />
 
* ''{{lang|cop-Latn|Klaria}}'' ([[Coptic language|Coptic]]) (an ''Armlet'')<ref name="hinkley63" />
 
* ''Yedelgeuse''
 
* ''Yedelgeuse''
  
In Chinese, Betelgeuse is known as {{lang|zh|参宿四}} ''({{lang|zh-Latn|Shēnsùsì}}, the Fourth Star of the Constellation of Three Stars)'' because the Constellation of Three Stars was at first a name for only three stars in the girdle of the Orion. Four more stars were later added to this constellation but the earlier name stuck.
+
In Chinese, Betelgeuse is known as ''{{lang|zh-Latn|Shēnsùsì}}'' ({{lang|zh|参宿四}}), or the "Fourth Star of the Constellation of Three Stars," because the Constellation of Three Stars was at first a name for only three stars in the girdle of the Orion. Four more stars were later added to this constellation, but the earlier name stuck.
 +
 
 +
Given its rich reddish color, Betelgeuse has also been called "the [[military|martial]] one," and in [[astrology]] it portends military or civic honors.
  
==Observation==
+
==Observations==
  
Betelgeuse's variability in brightness was first described by Sir [[John Herschel]] in 1836 when he published his observations of the star in ''Outlines of Astronomy'', noting the variations increased between 1836-1840, then decreased again. In 1849 he noted a shorter cycle of variability which peaked in 1852. Later observers recorded unusually high maxima with an interval of several years but only small variations between 1957 and 1967. Records of the [[American Association of Variable Star Observers]] show maximum brightnesses of magnitude 0.2 in 1933 and 1942, with minimums below magnitude 1.2 in 1927 and 1941.<ref>Burnham, Robert Jr. 1978. ''Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System'', Volume 2. New York, NY: Courier Dover Publications. ISBN 0486235688. page 1290.</ref>
+
Betelgeuse is the second brightest [[star]] in the [[constellation]] [[Orion (constellation)|Orion]] and the ninth [[list of brightest stars|brightest star]] in the night sky. Although it has the [[Bayer designation]] ''alpha,'' [[Rigel]] (Beta Orionis) is usually brighter. Yet, as a variable star, Betelgeuse is occasionally brighter than Rigel.
  
In 1919 [[Albert Abraham Michelson|Albert Michelson]] and [[Francis G. Pease|Francis Pease]] mounted a 6-metre (20 ft) interferometer on the front of the 2.5 meter (100-inch) [[telescope]] at [[Mount Wilson Observatory]]. Helped by John A. Anderson, in December 1920 Pease measured the angular diameter of α Orionis as 0.047&nbsp;[[arcsecond]]s. Given the then-current [[parallax]] value of 0.018&nbsp;arcseconds, this resulted in an estimated radius of 3.84&nbsp;&times;&nbsp;10<sup>8</sup>&nbsp;km (240&nbsp;million miles). However there was known uncertainty owing to limb darkening and measurement errors.<ref>A.A. Michelson, and F.G. Pease. 1921. [http://adsabs.harvard.edu/abs/1921ApJ....53..249M Measurement of the diameter of alpha Orionis with the interferometer.] ''Astrophysical Journal.'' 53:249–259. Retrieved November 11, 2008.</ref><ref>Staff. 2000. [http://eaa.crcpress.com/default.asp?action=summary&articleId=3915 Pease, Francis G (1881–1938). ''Encyclopedia of Astronomy and Astrophysics.'' Retrieved November 11, 2008.</ref> More recent visible-light observations of Betelgeuse have found the diameter to vary between 0.0568 and 0.0592&nbsp;[[arcsecond]]s.
+
Betelgeuse's variability in brightness was first described by Sir [[John Herschel]] in 1836 when he published his observations of the star in ''Outlines of Astronomy,'' noting the variations increased between 1836-1840, then decreased again. In 1849 he noted a shorter cycle of variability which peaked in 1852. Later observers recorded unusually high maxima with an interval of several years but only small variations between 1957 and 1967. Records of the [[American Association of Variable Star Observers]] show maximum brightnesses of magnitude 0.2 in 1933 and 1942, with minimums below magnitude 1.2 in 1927 and 1941.<ref>Robert Burnham, Jr. 1978. ''Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System,'' Volume 2. (New York, NY: Courier Dover Publications. ISBN 0486235688), 1290.</ref>
  
In the late 1980s and early 1990s Betelgeuse became a regular target for [[Aperture Masking Interferometry]] visible-light imaging, revealing a number of bright spots on the star's surface, which were thought to result from convection.<ref>Buscher, D. et al. 1990. [http://adsabs.harvard.edu/cgi-bin/bib_query?1990MNRAS.245p...7B. Detection of a bright feature on the surface of Betelgeuse.] ''Monthly Notices of the Royal Astronomical Society.'' 245:7.; Wilson, R. et al. 1997. [http://adsabs.harvard.edu/cgi-bin/bib_query?1997MNRAS.291..819W The changing face of Betelgeuse.] ''Monthly Notices of the Royal Astronomical Society.'' 291:819. Retrieved November 11, 2008.</ref> In 1995 the Faint Object Camera on the [[Hubble Space Telescope]] was used to capture the first conventional-telescope image (or "direct-image" in NASA terminology) of Betelgeuse (this was the first of any star other than the Sun). The ultra-violet image revealed a bright patch on the southwestern portion of the star's surface. This patch had a higher temperature than the surrounding stellar [[photosphere]]. Visual observation has shown Betelgeuse's rotation axis has an inclination of about 20° to the direction of Earth and a position (or height) angle of about 55°. Hence, the hot spot seen in 1995 is likely one of the star's poles.<ref name="uitenbroek_1998" />
+
In 1919, [[Albert Abraham Michelson|Albert Michelson]] and [[Francis G. Pease|Francis Pease]] mounted a 6-meter (20-foot) interferometer on the front of the 2.5 meter (100-inch) [[telescope]] at [[Mount Wilson Observatory]]. Helped by John A. Anderson, in December 1920 Pease measured the angular diameter of α Orionis as 0.047&nbsp;[[arcsecond]]s. Given the then-current [[parallax]] value of 0.018&nbsp;arcseconds, this resulted in an estimated radius of 3.84&nbsp;&times;&nbsp;10<sup>8</sup>&nbsp;km (240&nbsp;million miles). However there was known uncertainty owing to limb darkening and measurement errors.<ref>A.A. Michelson, and F.G. Pease. 1921. [http://www.adsabs.harvard.edu/abs/1921ApJ....53..249M Measurement of the diameter of alpha Orionis with the interferometer.] ''Astrophysical Journal'' 53:249–259. Retrieved November 11, 2008.</ref><ref>Staff. 2000. [http://eaa.crcpress.com/default.asp?action=summary&articleId=3915 Pease, Francis G (1881–1938). ''Encyclopedia of Astronomy and Astrophysics.'' Retrieved November 11, 2008.</ref> More recent visible-light observations of Betelgeuse have found the diameter to vary between 0.0568 and 0.0592&nbsp;arcseconds.  
  
Recent [[infrared]] measurements of the disk of Betelgeuse gave a mid-infrared [[angular diameter]] of 54.7&nbsp;±&nbsp;0.3&nbsp;[[Minute of arc|milli-arcseconds]] in November 1999, slightly smaller than the typical visible-light angular diameter. These measurements ignored any possible contribution from hotspots (which are less-noticeable in the mid-infrared) but factored-in some [[limb darkening]], whereby the intensity of a star's image diminishes near the edge. Some adjustment is needed to compensate for gas near the photosphere of Betelgeuse.<ref>Weiner, J. et al. 2000. [http://www.journals.uchicago.edu/doi/full/10.1086/317264 Precision Measurements of the Diameters of &alpha; Orionis and &omicron; Ceti at 11 Microns.] ''The Astrophysical Journal.'' 544(2):1097–1100. Retrieved November 11, 2008.</ref>
+
In the late 1980s and early 1990s, Betelgeuse became a regular target for [[Aperture Masking Interferometry]] visible-light imaging, revealing a number of bright spots on the star's surface, which were thought to result from convection.<ref>D. Buscher, et al. 1990. [http://adsabs.harvard.edu/cgi-bin/bib_query?1990MNRAS.245p...7B. Detection of a bright feature on the surface of Betelgeuse.] ''Monthly Notices of the Royal Astronomical Society'' 245:7.; R. Wilson, et al. 1997. [http://adsabs.harvard.edu/cgi-bin/bib_query?1997MNRAS.291..819W The changing face of Betelgeuse.] ''Monthly Notices of the Royal Astronomical Society'' 291:819. Retrieved November 11, 2008.</ref> In 1995 the Faint Object Camera on the [[Hubble Space Telescope]] was used to capture the first conventional-telescope image (or "direct-image" in NASA terminology) of Betelgeuse (this was the first of any star other than the Sun). The ultra-violet image revealed a bright patch on the southwestern portion of the star's surface. This patch had a higher temperature than the surrounding stellar [[photosphere]]. Visual observation has shown Betelgeuse's rotation axis has an inclination of about 20° to the direction of Earth and a position (or height) angle of about 55°. Hence, the hot spot seen in 1995 is likely one of the star's poles.<ref name="uitenbroek_1998" />
 +
 
 +
Recent [[infrared]] measurements of the disk of Betelgeuse gave a mid-infrared [[angular diameter]] of 54.7&nbsp;±&nbsp;0.3&nbsp;[[Minute of arc|milli-arcseconds]] in November 1999, slightly smaller than the typical visible-light angular diameter. These measurements ignored any possible contribution from hotspots (which are less-noticeable in the mid-infrared) but factored-in some [[limb darkening]], whereby the intensity of a star's image diminishes near the edge. Some adjustment is needed to compensate for gas near the photosphere of Betelgeuse.<ref>J. Weiner, et al. 2000. [http://www.journals.uchicago.edu/doi/full/10.1086/317264 Precision Measurements of the Diameters of &alpha; Orionis and &omicron; Ceti at 11 Microns.] ''The Astrophysical Journal'' 544(2):1097–1100. Retrieved November 11, 2008.</ref>
  
 
===Observed size===
 
===Observed size===
[[Image:Betelgeuse star (Hubble).jpg|thumb|Betelgeuse imaged in [[ultraviolet]] light by the [[Hubble Space Telescope]] and subsequently enhanced by NASA. The bright white spot is likely one of its poles. ''[[NASA]]/[[ESA]] credit.''<ref>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]].
+
[[File:Betelgeuse – NASA.jpg|thumb|Betelgeuse imaged in [[ultraviolet]] light by the [[Hubble Space Telescope]] and subsequently enhanced by NASA. The bright white spot is likely one of its poles. ''[[NASA]]/[[ESA]] credit.''<ref>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.</ref><ref>Ronald Gilliland and A. K. Dupree. May 1996. [http://www.adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...463L..29G First Image of the Surface of a Star with the Hubble Space Telescope.] ''Astrophysical Journal Letters'' 463:L29. Retrieved November 11, 2008.</ref>]]
The actual images were oversampled by a factor of 5 with bicubic spline interpolation, then deconvolved.</ref><ref>Gilliland, Ronald, and A.K. Dupree. [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...463L..29G First Image of the Surface of a Star with the Hubble Space Telescope.] ''Astrophysical Journal Letters.'' 463:L29. Retrieved November 11, 2008.</ref>]]
+
[[Image:Light curve of Betelgeuse.png|thumb|[[AAVSO]] [[Photometric system|V-band]] [[light curve]] of Betelgeuse (Alpha Orionis) from Dec. 1988 to Aug. 2002.]]
[[Image:Light curve of Betelgeuse.png|thumb|[[AAVSO]] [[Photometric system|V-band]] [[light curve]] of Betelgeuse (Alpha Orionis) from Dec. 1988 - Aug. 2002 ]]
 
  
Betelgeuse has several features which are of particular interest to astronomers. Because of the size and proximity of this star it has the third largest [[angular diameter]] as viewed from Earth,<ref name="bedding_1997">Bedding, T.R. et al. 1997. [http://adsabs.harvard.edu/abs/1997astro.ph..1021B The angular diameter of R Doradus: a nearby Mira-like star.] ''Monthly Notices of the Royal Astronomical Society.'' 286(4):957–962. Retrieved November 11, 2008.</ref> smaller only than the Sun and [[R Doradus]]. Moreover, it is one of only a dozen or so stars telescopes have imaged as a visible disk. The angular diameter of Betelgeuse was one of the first to be measured with an [[astronomical interferometer]] and the apparent diameter was found to be variable. The distance to Betelgeuse is not known with precision but if this is assumed to be 640 [[light years]], the star's diameter would be about 950 to 1000 times that of the Sun. Betelgeuse has a color index (B-V) of 1.86 and is thought to have a mass of about 20 solar masses.<ref name="uiuc">Kaler, Jim. 2008. [http://www.astro.uiuc.edu/~kaler/sow/betelgeuse.html Betelgeuse (Alpha Orionis).] ''Stars''. Retrieved November 11, 2008.</ref>
+
Betelgeuse has several features of particular interest to astronomers. Because of the size and proximity of this star, it has the third largest [[angular diameter]] as viewed from Earth,<ref name="bedding_1997">T.R. Bedding, et al. 1997. [http://adsabs.harvard.edu/abs/1997astro.ph..1021B The angular diameter of R Doradus: a nearby Mira-like star.] ''Monthly Notices of the Royal Astronomical Society'' 286(4):957–962. Retrieved November 11, 2008.</ref> smaller only than the Sun and [[R Doradus]]. Moreover, it is one of only a dozen or so stars telescopes have imaged as a visible disk. The angular diameter of Betelgeuse was one of the first to be measured with an [[astronomical interferometer]] and the apparent diameter was found to be variable. The distance to Betelgeuse is not known with precision but if this is assumed to be 640 [[light years]], the star's diameter would be about 950 to 1000 times that of the Sun. Betelgeuse has a color index (B-V) of 1.86 and is thought to have a mass of about 20 solar masses.<ref name="uiuc">Jim Kaler, ''Stars'' 2008. [http://www.astro.uiuc.edu/~kaler/sow/betelgeuse.html Betelgeuse (Alpha Orionis).] ''University of Illinois''. Retrieved November 11, 2008.</ref>
  
The precise diameter is hard to define since optical emissions decrease very gradually with radius from the center of Betelgeuse and the color of these emissions also vary with radius. Though only 20 times more massive than the Sun, this star could be hundreds of millions times greater in volume (as with a [[beach ball]] compared to a large [[stadium]]). Betelgeuse was the first star on which starspots were resolved in optical images by a telescope, first from [[Aperture Masking Interferometry]] and later from the Hubble Space Telescope along with more detailed observations by the COAST telescope.<ref>Burns, D. et al. 1997. [http://adsabs.harvard.edu/cgi-bin/bib_query?1997MNRAS.290L..11B%26db_key=AST The surface structure and limb-darkening profile of Betelgeuse.] ''Monthly Notices of the Royal Astronomical Society.'' 290(1):L11–L16. Retrieved November 11, 2008.</ref><ref name="uiuc"/>
+
The precise diameter is hard to define since optical emissions decrease very gradually with radius from the center of Betelgeuse and the color of these emissions also vary with radius. Though only 20 times more massive than the Sun, this star could be hundreds of millions times greater in volume (as with a [[beach ball]] compared to a large [[stadium]]). Betelgeuse was the first star on which starspots were resolved in optical images by a telescope, first from [[Aperture Masking Interferometry]] and later from the Hubble Space Telescope along with more detailed observations by the COAST telescope.<ref>D. Burns, et al. 1997. [http://adsabs.harvard.edu/cgi-bin/bib_query?1997MNRAS.290L..11B%26db_key=AST The surface structure and limb-darkening profile of Betelgeuse.] ''Monthly Notices of the Royal Astronomical Society'' 290(1):L11–L16. Retrieved November 11, 2008.</ref><ref name="uiuc"/>
  
 
Betelgeuse's [[photosphere]] has an extended atmosphere which displays strong lines of emission (rather than absorption). This [[chromosphere]] has a temperature no higher than 5,500&nbsp;K and may stretch outward to 7 times the diameter of the star. This extended gaseous atmosphere has been observed moving both away from and towards Betelgeuse, apparently depending on radial velocity fluctuations in the photosphere.<ref name="apj545" />
 
Betelgeuse's [[photosphere]] has an extended atmosphere which displays strong lines of emission (rather than absorption). This [[chromosphere]] has a temperature no higher than 5,500&nbsp;K and may stretch outward to 7 times the diameter of the star. This extended gaseous atmosphere has been observed moving both away from and towards Betelgeuse, apparently depending on radial velocity fluctuations in the photosphere.<ref name="apj545" />
  
==Betelgeuse's fate==
+
==Fate of the star==
It is likely that Betelgeuse will go [[supernova]].<ref name=EarthskyOrg/><ref name="uiuc"/> Considering its size and apparent young age of only 8.5 million years, it may explode within the next thousand years, or may have already.<ref name=EarthskyOrg/> Since its rotational axis is not toward the Earth, Betelgeuse's supernova might not cause a [[gamma ray burst]] in the direction of Earth large enough to damage its [[ecosystem]] even from a relatively close proximity of 640 light years.<ref name=EarthskyOrg/> However, a Betelgeuse supernova could easily outshine the [[Moon]] in the night sky.<ref name=EarthskyOrg>Byrd, Deborah, Joel Block,
+
It seems likely that Betelgeuse will become a [[supernova]].<ref name=EarthskyOrg/><ref name="uiuc"/> Considering its size and apparent young age of only 8.5 million years, it may explode within the next thousand years, or may have already.<ref name=EarthskyOrg/> Since its rotational axis is not toward the Earth, Betelgeuse's supernova might not cause a [[gamma ray burst]] in the direction of Earth large enough to damage its [[ecosystem]] even from a relatively close proximity of 640 light years.<ref name=EarthskyOrg/> However, a Betelgeuse supernova could easily outshine the [[Moon]] in the night sky.<ref name=EarthskyOrg>Deborah Byrd, Joel Block,
Lindsay Patterson, and Jorge Salazar. [http://www.earthsky.org/radioshows/48792/betelgeuse-could-become-supernova Betelgeuse could explode as a supernova, Radio Podcasts &#124.] Earth & Sky. Retrieved November 11, 2008.</ref>
+
Lindsay Patterson, and Jorge Salazar. [http://www.earthsky.org/radioshows/48792/betelgeuse-could-become-supernova Betelgeuse could explode as a supernova, Radio Podcasts &#124.] ''Earth & Sky''. Retrieved November 11, 2008.</ref>
  
 
==See also==
 
==See also==
  
*[[List of largest known stars]]
+
* [[Constellation]]
 
* [[Red giant]]
 
* [[Red giant]]
*[[Star]]
+
* [[Star]]
 +
* [[Sun]]
  
 
== Notes ==
 
== Notes ==
Line 100: Line 107:
  
 
==References==
 
==References==
* Allen, Richard Hinckley. 1963. ''Star Names: Their Lore and Meaning''. New York, NY: Dover Publications. ISBN 0486210790.
+
* Allen, Richard Hinckley. ''Star Names: Their Lore and Meaning''. New York, NY: Dover Publications, 1963. ISBN 0486210790
* Burnham, Robert Jr. 1978. ''Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System'', Volume 2. New York, NY: Courier Dover Publications. ISBN 0486235688.
+
* Burnham, Robert Jr. ''Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System'', Volume 2. New York, NY: Courier Dover Publications, 1978. ISBN 0486235688
* Kunitzsch, Paul, and Tim Smart. 2006. ''A Dictionary of Modern Star Names''. Cambridge, MA: Sky Publishing. ISBN 9781931559447.
+
* Kunitzsch, Paul, and Tim Smart. ''A Dictionary of Modern Star Names''. Cambridge, MA: Sky Publishing, 2006. ISBN 978-1931559447
*Tuthill, Peter G., Chris A. Haniff, and John E. Baldwin. 1997. Hotspots on late-type supergiants. ''Monthly Notices of the Royal Astronomical Society.'' 285(3):529–539.
+
*Tuthill, Peter G., Chris A. Haniff, and John E. Baldwin. Hotspots on late-type supergiants. ''Monthly Notices of the Royal Astronomical Society.'' 285(3) (1997):529–539.
  
 
==External Links==
 
==External Links==
 
+
All links retrieved January 21, 2022.
* Davis, Kate. 2000. [http://www.aavso.org/vstar/vsots/1200.shtml Variable Star of the Month&mdash;December, 2000: Alpha Orionis.] AAVSO. Retrieved November 11, 2008.
+
*[http://uk.arxiv.org/pdf/astro-ph/0402099 Interferometric observations of the supergiant stars α Orionis and α Herculis with FLUOR at IOTA], February 2004. Retrieved November 11, 2008.
+
*[http://arxiv.org/abs/astro-ph/0606387 Invisible Giant: Chandra's Limits on X-rays from Betelgeuse].  
*[http://www.astro.ku.dk/~dorch/paper/copies/Dorch2004.pdf Magnetic activity in late-type giant stars: Numerical MHD simulations of non-linear dynamo action in Betelgeuse]. Retrieved November 11, 2008.
+
* [http://www.solstation.com/x-objects/betelgeuse.htm Betelgeuse.] SolStation.  
*[http://arxiv.org/abs/astro-ph/0606387 Invisible Giant: Chandra's Limits on X-rays from Betelgeuse]. Retrieved November 11, 2008.
 
* Young, John. 2006. [http://www.mrao.cam.ac.uk/telescopes/coast/betel.html Surface imaging of Betelgeuse with COAST and the WHT.] University of Cambridge. Retrieved November 11, 2008. &mdash; Images of hotspots on the surface of Betelgeuse taken at visible and infra-red wavelengths using high resolution ground-based [[astronomical interferometer|interferometers]].
 
* [http://www.solstation.com/x-objects/betelgeuse.htm Betelgeuse.] SolStation. Retrieved November 11, 2008.
 
  
 
[[Category:Physical sciences]]
 
[[Category:Physical sciences]]

Revision as of 15:43, 21 January 2022

This article is about the star.
Betelgeuse, Alpha Ori
Position Alpha Ori.png
Betelgeuse is the upper left star (pink arrow) in the rectangle of bright stars in Orion.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Orion
Right ascension 05h 55m 10.3053s[1]
Declination +07° 24′ 25.426″[1]
Apparent magnitude (V)0.58[1] (0.3 to 1.2)
Characteristics
Spectral typeM2Iab[1]
U-B color index2.06[1]
B-V color index1.85[1]
Variable typeSR c[1] (Semi-regular)
Astrometry
Radial velocity (Rv)+21.0[1] km/s
Proper motion (μ) RA: 24.95 ± 0.08[2] mas/yr
Dec.: 9.56 ± 0.15[2] mas/yr
Parallax (π)5.07 ± 1.10[2] mas
Distanceapprox. 600 ly
(approx. 200 pc)
Absolute magnitude (MV)−5.14
Details
Mass20[3] M
Radius950-1000[3] R
Surface gravity (log g)-0.5[4]
Luminosity135,000[3] L
Temperature3,500[4] K
Rotation17 years (14.6 km/s)[5]
Age1.0 × 107 years
Other designations
Alpha Orionis, 58 Ori, HR 2061, BD+7°1055, HD 39801, SAO 113271, FK5 224, HIP 27989.[1]

Betelgeuse (also called Alpha Orionis, α Orionis, or α Ori) is one of the brightest and largest known stars, though it is not one of the most massive. Located approximately 600 light-years from Earth, it is part of the constellation Orion and a vertex of the Winter Triangle asterism. Its large volume suggests that if it were at the center of the Solar System, it would wholly engulf Mercury, Venus, Earth, and Mars, with its surface extending out to between the orbits of Mars and Jupiter. It is classified as a red supergiant and as a semiregular variable star—that is, it shows considerable periodicity as its light changes, but this periodicity is sometimes irregular.

Etymology

The name Betelgeuse is a corruption of the Arabic yad al-jawzā (يد الجوزاء), meaning "hand of the central one." The Arabs had earlier called Gemini Jauza ("the central one") but later switched this name to Orion.

European mistransliteration into Latin during the Middle Ages led to the first character y (, with two dots underneath) being misread as a b (, with only one dot underneath). Thus throughout the Renaissance, the star's name was written as Bait al-Jauza and thought to mean armpit of the central one in Arabic. This led to the modern rendering as Betelgeuse (although a true translation of "armpit" would be ابط, transliterated as Ibţ,[6] hence in 1899 Richard Hinckley Allen mistakenly gave the origin as Ibţ al Jauzah).[7] In German, the star's name was corrupted even further: it is called Beteigeuze, because the letter l in the Romanized name was mistaken for the letter i.

Variety of names

Betelgeuse has been called by many other names. Some examples are:

  • Al Dhira (the Arm)[7]
  • Al Mankib (the Shoulder)[7]
  • Al Yad al Yamma (the Right Hand)[7]
  • Ardra (Hindi,[7] and name of Hindu Nakshatra)
  • Bahu (Sanskrit)[7]
  • Bašn (Persian) (the Arm),
  • Gula (Euphratean)
  • Ied Algeuze (Orion's Hand)[7]
  • Klaria (Coptic) (an Armlet)[7]
  • Yedelgeuse

In Chinese, Betelgeuse is known as Shēnsùsì (参宿四), or the "Fourth Star of the Constellation of Three Stars," because the Constellation of Three Stars was at first a name for only three stars in the girdle of the Orion. Four more stars were later added to this constellation, but the earlier name stuck.

Given its rich reddish color, Betelgeuse has also been called "the martial one," and in astrology it portends military or civic honors.

Observations

Betelgeuse is the second brightest star in the constellation Orion and the ninth brightest star in the night sky. Although it has the Bayer designation alpha, Rigel (Beta Orionis) is usually brighter. Yet, as a variable star, Betelgeuse is occasionally brighter than Rigel.

Betelgeuse's variability in brightness was first described by Sir John Herschel in 1836 when he published his observations of the star in Outlines of Astronomy, noting the variations increased between 1836-1840, then decreased again. In 1849 he noted a shorter cycle of variability which peaked in 1852. Later observers recorded unusually high maxima with an interval of several years but only small variations between 1957 and 1967. Records of the American Association of Variable Star Observers show maximum brightnesses of magnitude 0.2 in 1933 and 1942, with minimums below magnitude 1.2 in 1927 and 1941.[8]

In 1919, Albert Michelson and Francis Pease mounted a 6-meter (20-foot) interferometer on the front of the 2.5 meter (100-inch) telescope at Mount Wilson Observatory. Helped by John A. Anderson, in December 1920 Pease measured the angular diameter of α Orionis as 0.047 arcseconds. Given the then-current parallax value of 0.018 arcseconds, this resulted in an estimated radius of 3.84 × 108 km (240 million miles). However there was known uncertainty owing to limb darkening and measurement errors.[9][10] More recent visible-light observations of Betelgeuse have found the diameter to vary between 0.0568 and 0.0592 arcseconds.

In the late 1980s and early 1990s, Betelgeuse became a regular target for Aperture Masking Interferometry visible-light imaging, revealing a number of bright spots on the star's surface, which were thought to result from convection.[11] In 1995 the Faint Object Camera on the Hubble Space Telescope was used to capture the first conventional-telescope image (or "direct-image" in NASA terminology) of Betelgeuse (this was the first of any star other than the Sun). The ultra-violet image revealed a bright patch on the southwestern portion of the star's surface. This patch had a higher temperature than the surrounding stellar photosphere. Visual observation has shown Betelgeuse's rotation axis has an inclination of about 20° to the direction of Earth and a position (or height) angle of about 55°. Hence, the hot spot seen in 1995 is likely one of the star's poles.[5]

Recent infrared measurements of the disk of Betelgeuse gave a mid-infrared angular diameter of 54.7 ± 0.3 milli-arcseconds in November 1999, slightly smaller than the typical visible-light angular diameter. These measurements ignored any possible contribution from hotspots (which are less-noticeable in the mid-infrared) but factored-in some limb darkening, whereby the intensity of a star's image diminishes near the edge. Some adjustment is needed to compensate for gas near the photosphere of Betelgeuse.[12]

Observed size

Betelgeuse imaged in ultraviolet light by the Hubble Space Telescope and subsequently enhanced by NASA. The bright white spot is likely one of its poles. NASA/ESA credit.[13][14]
AAVSO V-band light curve of Betelgeuse (Alpha Orionis) from Dec. 1988 to Aug. 2002.

Betelgeuse has several features of particular interest to astronomers. Because of the size and proximity of this star, it has the third largest angular diameter as viewed from Earth,[15] smaller only than the Sun and R Doradus. Moreover, it is one of only a dozen or so stars telescopes have imaged as a visible disk. The angular diameter of Betelgeuse was one of the first to be measured with an astronomical interferometer and the apparent diameter was found to be variable. The distance to Betelgeuse is not known with precision but if this is assumed to be 640 light years, the star's diameter would be about 950 to 1000 times that of the Sun. Betelgeuse has a color index (B-V) of 1.86 and is thought to have a mass of about 20 solar masses.[3]

The precise diameter is hard to define since optical emissions decrease very gradually with radius from the center of Betelgeuse and the color of these emissions also vary with radius. Though only 20 times more massive than the Sun, this star could be hundreds of millions times greater in volume (as with a beach ball compared to a large stadium). Betelgeuse was the first star on which starspots were resolved in optical images by a telescope, first from Aperture Masking Interferometry and later from the Hubble Space Telescope along with more detailed observations by the COAST telescope.[16][3]

Betelgeuse's photosphere has an extended atmosphere which displays strong lines of emission (rather than absorption). This chromosphere has a temperature no higher than 5,500 K and may stretch outward to 7 times the diameter of the star. This extended gaseous atmosphere has been observed moving both away from and towards Betelgeuse, apparently depending on radial velocity fluctuations in the photosphere.[4]

Fate of the star

It seems likely that Betelgeuse will become a supernova.[17][3] Considering its size and apparent young age of only 8.5 million years, it may explode within the next thousand years, or may have already.[17] Since its rotational axis is not toward the Earth, Betelgeuse's supernova might not cause a gamma ray burst in the direction of Earth large enough to damage its ecosystem even from a relatively close proximity of 640 light years.[17] However, a Betelgeuse supernova could easily outshine the Moon in the night sky.[17]

See also

Notes

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 SIMBAD query result: V* alf Ori—Semi-regular pulsating Star. Centre de Données astronomiques de Strasbourg. Retrieved November 11, 2008.
  2. 2.0 2.1 2.2 Graham M. Harper, Alexander Brown, and Edward F. Guinan. 2008. A New VLA-Hipparcos Distance to Betelgeuse and its Implications. The Astronomical Journal 135(4):1430-1440. (5), Table 6. Retrieved November 11, 2008.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Jim Kaler, Stars 2008. Betelgeuse (Alpha Orionis). University of Illinois. Retrieved November 11, 2008.
  4. 4.0 4.1 4.2 A. Lobel, and A.K. Dupree. 2000. Modeling the Variable Chromosphere of α Orionis. The Astrophysical Journal 545:454–474. Retrieved November 11, 2008.
  5. 5.0 5.1 H. Uitenbroek, A.K. Dupree, and R.L. Gilliland. 1998. Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of α Orionis. The Astronomical Journal 116:2501–2512. Retrieved November 11, 2008.
  6. Paul Kunitzsch and Tim Smart. 2006. A Dictionary of Modern Star Names. (Cambridge, MA: Sky Publishing. ISBN 9781931559447), 45.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Richard Hinckley Allen, 1963. Star Names: Their Lore and Meaning. (New York, NY: Dover Publications. ISBN 0486210790).
  8. Robert Burnham, Jr. 1978. Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Volume 2. (New York, NY: Courier Dover Publications. ISBN 0486235688), 1290.
  9. A.A. Michelson, and F.G. Pease. 1921. Measurement of the diameter of alpha Orionis with the interferometer. Astrophysical Journal 53:249–259. Retrieved November 11, 2008.
  10. Staff. 2000. [http://eaa.crcpress.com/default.asp?action=summary&articleId=3915 Pease, Francis G (1881–1938). Encyclopedia of Astronomy and Astrophysics. Retrieved November 11, 2008.
  11. D. Buscher, et al. 1990. Detection of a bright feature on the surface of Betelgeuse. Monthly Notices of the Royal Astronomical Society 245:7.; R. Wilson, et al. 1997. The changing face of Betelgeuse. Monthly Notices of the Royal Astronomical Society 291:819. Retrieved November 11, 2008.
  12. J. Weiner, et al. 2000. Precision Measurements of the Diameters of α Orionis and ο Ceti at 11 Microns. The Astrophysical Journal 544(2):1097–1100. Retrieved November 11, 2008.
  13. 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.
  14. Ronald Gilliland and A. K. Dupree. May 1996. First Image of the Surface of a Star with the Hubble Space Telescope. Astrophysical Journal Letters 463:L29. Retrieved November 11, 2008.
  15. T.R. Bedding, et al. 1997. The angular diameter of R Doradus: a nearby Mira-like star. Monthly Notices of the Royal Astronomical Society 286(4):957–962. Retrieved November 11, 2008.
  16. D. Burns, et al. 1997. The surface structure and limb-darkening profile of Betelgeuse. Monthly Notices of the Royal Astronomical Society 290(1):L11–L16. Retrieved November 11, 2008.
  17. 17.0 17.1 17.2 17.3 Deborah Byrd, Joel Block, Lindsay Patterson, and Jorge Salazar. Betelgeuse could explode as a supernova, Radio Podcasts &#124. Earth & Sky. Retrieved November 11, 2008.

References
ISBN links support NWE through referral fees

  • Allen, Richard Hinckley. Star Names: Their Lore and Meaning. New York, NY: Dover Publications, 1963. ISBN 0486210790
  • Burnham, Robert Jr. Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Volume 2. New York, NY: Courier Dover Publications, 1978. ISBN 0486235688
  • Kunitzsch, Paul, and Tim Smart. A Dictionary of Modern Star Names. Cambridge, MA: Sky Publishing, 2006. ISBN 978-1931559447
  • Tuthill, Peter G., Chris A. Haniff, and John E. Baldwin. Hotspots on late-type supergiants. Monthly Notices of the Royal Astronomical Society. 285(3) (1997):529–539.

External Links

All links retrieved January 21, 2022.

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.