Algol
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2008-07-10T17:45:54Z
Kbdankbot
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Robot - move category per [[WP:CFD|CFD]] [[Wikipedia:Categories for discussion/Log/2008 July 2|2008 July 2]]
{{Otheruses}}
{{Starbox begin |
name=Beta Persei A/B/C }}
{{Starbox image |
image=[[Image:Position Beta Per.png|250px]] |
caption=The position of Algol. }}
{{Starbox observe |
epoch=J2000 |
ra={{RA|03|08|10.1315}}<ref name=simbada>[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=name+algol+a Database entry for Algol A], [[SIMBAD]]. Accessed online [[February 9]], [[2008]].</ref> |
dec={{DEC| +40|57|20.332}}<ref name=simbada/> |
appmag_v=2.12<ref name=simbada/> |
constell=[[Perseus (constellation)|Perseus]] }}
{{Starbox character |
class=B8V (A)<ref name=simbada/> /K02IV (B)<ref name=simbadb>[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=name+algol+b Database entry for Algol B], [[SIMBAD]]. Accessed online [[February 9]], [[2008]].</ref> /A5V (C) |
b-v=-0.05 |
u-b=-0.37 |
variable=[[Eclipsing binary]] }}
{{Starbox astrometry |
radial_v=3.7 |
prop_mo_ra=2.39 |
prop_mo_dec=-1.44 |
parallax=35.14 |
p_error=0.90 |
absmag_v=-0.15 }}
{{Starbox detail|
mass=3.59/0.79/1.67 |
radius=2.3/3.0/0.9 |
luminosity=98/3.4/4.1 |
temperature=12,000/4,500/8,500 |
metal=''Not available'' |
rotation=65 km/s. |
age=< 3 × 10<sup>8</sup> }}
{{Starbox catalog |
names=Algol, Gorgona, Gorgonea Prima, Demon Star, El Ghoul, 26 Per, [[Gliese-Jahreiss catalogue|GJ]] 9110, [[Harvard Revised catalogue|HR]] 936, [[Bonner Durchmusterung|BD]] +40°673, [[Henry Draper catalogue|HD]] 19356, [[General Catalogue of Trigonometric Parallaxes|GCTP]] 646.00, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 38592, FK5 111, Wo 9110, ADS 2362, WDS 03082+4057A, [[Hipparcos catalogue|HIP]] 14576. }}
{{Starbox end}}
'''Algol''' (β Per / [[beta (letter)|Beta]] Persei), known colloquially as the '''Demon Star''', is a bright [[star]] in the [[constellation]] [[Perseus (constellation)|Perseus]]. It is one of the best known [[eclipsing binary|eclipsing binaries]], the first such star to be discovered, and also one of the first (non-[[nova]]) [[variable star]]s to be discovered. Algol is actually a three-star system (Beta Persei A, B and C) in which the large and bright primary Beta Persei A is regularly eclipsed by the dimmer Beta Persei B. Thus, Algol's [[apparent magnitude|magnitude]] is usually near-constant at 2.1, but regularly dips to 3.4 every 2 days, 20 hours and 49 minutes during the roughly 10-hour long partial eclipses. There is also a secondary eclipse when the brighter star occults the fainter secondary. This secondary eclipse can only be detected photoelectrically.<ref>Beta Persei, American Association of Variable Star Observers. http://www.aavso.org/vstar/vsots/0199.shtml</ref>
==Observation history==
The variability of Algol was first recorded in 1667 by [[Geminiano Montanari]], but it is probable that this property was noticed long before this time. The first person to propose a mechanism for the variability of this star was the British amateur astronomer [[John Goodricke]]. In May, 1783 he presented his findings to the [[Royal Society]], suggesting that the periodic variability was caused by a dark body passing in front of the star (or else that the star itself has a darker region that is periodically turned toward the Earth.) For his report he was awarded the [[Copley Medal]].<ref>{{cite web | date = 2003-08-06 | url = http://www.surveyor.in-berlin.de/himmel/Bios/Goodricke-e.html | title = John Goodricke, The Discovery of the Occultating Variable Stars | language = English | accessdate = 2006-07-31 }}</ref>
In 1881, the Harvard astronomer [[Edward Pickering]] presented evidence that Algol was actually an eclipsing binary.<ref>{{cite journal | last = Pickering | first = Edward C. | title=Dimensions of the Fixed Stars, with especial reference to Binaries and Variables of the Algol type | journal=Astronomical register | year=1881 | pages=253–256 | url=http://adsabs.harvard.edu/abs/1881AReg...19..253. | doi=10.1007/BF00215914 | volume=50 }}</ref> This was confirmed a few years later, in 1889, when the Potsdam astronomer [[Hermann Vogel]] found periodic [[doppler shift]]s in the spectrum of Algol, inferring variations in the [[radial velocity]] of this binary system.<ref>{{cite journal | author = A. H. Batten | title=Two Centuries of Study of Algol Systems | journal=Space Science Reviews | year=1989 | volume=50 | issue=1/2 | pages=1–8 | url=http://adsabs.harvard.edu/abs/1989SSRv...50....1B
| doi = 10.1007/BF00215914 <!--Retrieved from url by DOI bot--> }}</ref> Thus Algol became one of the first known [[spectroscopic binary|spectroscopic binaries]].
==System==
As an eclipsing binary, it is actually two stars in close orbit around one another. Because the [[Orbital plane (astronomy)|orbital plane]] coincidentally contains the [[Earth]]'s line of sight, the dimmer star (Algol B) passes in front of the brighter star (Algol A) once per orbit, and the amount of light reaching Earth is temporarily decreased. To be more precise, however, Algol happens to be a triple star system: the eclipsing binary pair is separated by only 0.062 [[astronomical unit|AU]], while the third star (Algol C) is at an average distance of 2.69 AU from the pair and the mutual [[orbital period]] is 681 days (1.86 years). The total mass of the system is about 5.8 solar masses, and the mass ratios of A, B and C are about 4.5 : 1 : 2.
{| class="wikitable" style="margin: 1em auto 1em auto"
|+ ''Orbital Elements of the Algol System''
!Components
![[Semimajor axis]]
![[Orbital eccentricity|Ellipticity]]
![[Orbital period|Period]]
![[Inclination]]
|-
!A—B<ref>{{cite journal | author = L. A. Molnar, R. L. Mutel | title=Dynamical Evolution of the Algol Triple System | journal=Bulletin of the American Astronomical Society | year=1996 | volume=28 | pages=921 | url=http://adsabs.harvard.edu/abs/1996AAS...188.6014M | doi=10.1007/BF00215914 }}</ref>
|align="center"| 0.00218″
|align="center"| 0.00
|align="center"| 2.87 days
|align="center"| 97.69°
|-
!(AB)—C<ref>{{cite web | author = W.I. Hartkopf, B.D. Mason | date = 2006-07-30 | url =http://ad.usno.navy.mil/wds/orb6.html | title = Sixth Catalog of Orbits of Visual Binary Stars | publisher = U.S. Naval Observatory | language = English | accessdate = 2006-07-31 }}</ref>
|align="center"| 0.09461″
|align="center"| 0.225
|align="center"| 680.05 days
|align="center"| 83.98°
|}
Studies of Algol led to the '''[[Algol paradox]]''' in the theory of [[stellar evolution]]: although components of a binary star form at the same time, and massive stars evolve much faster than the less massive ones, it was observed that the more massive component Algol A is still in the [[main sequence]], while the less massive Algol B is a [[subgiant star]] at a later evolutionary stage. The paradox can be solved by [[mass transfer]]: when the more massive star became a subgiant, it filled its [[Roche lobe]], and most of the mass was transferred to the other star, which is still in the main sequence. In some binaries similar to Algol, a gas flow can be seen.<ref>{{cite journal | first=Izold | last=Pustylnik | title=On Accretion Component of the Flare Activity in Algol | journal=Baltic Astronomy | year=1995 | volume=4 | pages=64–78 | url=http://adsabs.harvard.edu/abs/1995BaltA...4...64P | doi=10.1007/BF00215914 }}</ref>
This system also exhibits variable activity in the form of [[x-ray]] and [[radio]] flares. The former is thought to be caused by the magnetic fields of the AB components interacting with the mass transfer.<ref>{{cite journal | author=M.J. Sarna, S.K. Yerli, A.G. Muslimov | title=Magnetic activity and evolution of Algol-type stars - II | journal=Monthly Notices of the Royal Astronomical Society | year=1998 | volume=297 | issue=3 | pages=760–768 | url=http://adsabs.harvard.edu/abs/1998MNRAS.297..760S | doi=10.1046/j.1365-8711.1998.01539.x }}</ref> The radio emissions may be created by magnetic cycles similar to [[sunspots]], but, as the magnetic fields around these stars are up to ten times stronger than that of the [[Sun]], these radio flares are more powerful and longer lasting.<ref>{{cite web | last = Blue | first = Charles E. | date = 2002-06-03 | url = http://www.nrao.edu/pr/2002/algol/ | title = Binary Stars "Flare" With Predictable Cycles, Analysis of Radio Observations Reveals | publisher = National Radio Astronomy Observatory | language = English | accessdate = 2006-07-31 }}</ref>
Algol is 92.8 [[light year]]s from Earth; however, about 7.3 million years ago it passed within 9.8 light years<ref>{{cite conference
| author=Garcia-Sanchez, J.; Preston, R. A.; Jones, D. L.; Lestrade, J.-F.; Weissman, P. R.; Latham, D. W.
| title =A Search for Stars Passing Close to the Sun
| booktitle =The First Results of Hipparcos and Tycho
| publisher =IAU | date =August 25, 1997 | location =Kyoto, Japan
| url =http://adsabs.harvard.edu/abs/1997IAUJD..14E..51G
| accessdate = 2007-06-01 }}</ref> and its [[apparent magnitude]] was approximately −2.5, considerably brighter than [[Sirius]] is today. Because the total mass of the system is 5.8 solar masses, and despite the fairly large distance at closest approach, this may have been enough to perturb the [[solar system]]'s [[Oort cloud]] slightly and to increase the number of [[comet]]s entering the inner solar system. However, the actual increase in net cratering rate is believed to have been quite small.<ref>{{cite journal | author = J. García-Sánchez, R.A. Preston, D.L. Jones, P.R. Weissman | title=Stellar Encounters with the Oort Cloud Based on Hipparcos Data | journal=The Astronomical Journal | year=1999 | volume=117 | pages=1042–1055 | url=http://www.iop.org/EJ/article/1538-3881/117/2/1042/980216.html | doi=10.1086/300723 }}</ref>
==Etymology and cultural significance==
The name Algol derives from [[Arabic language|Arabic]] '''رأس الغول''' ''ra's al-ghūl'' : head (ra's) of the ogre (al-ghūl) (see "the [[ghoul]]") which was probably given due to its peculiar behavior. The English names of ''Demon Star'' and ''Blinking Demon'' are direct translations.<ref name="allen">{{cite book | first=Richard Hinckley | last=Allen | title=Star Names: Their Lore and Meaning (revised edition) | publisher=Dover | year=1963|pages=p332-33| isbn= 0-486-21079-0}}</ref> In Hebrew folklore it was known as ''Rōsh ha Sāṭān'' 'Satan's Head', via [[Edmund Chilmead]], who called it 'Divels head' or ''Rosch hassatan''. A [[Latin]] term from the 16th century was ''Caput Larvae'' 'Spectre's Head'. It was also linked with [[Lilith]].<ref name="allen"/> In the [[constellation]] [[Perseus (constellation)|Perseus]], it represents the eye of the [[Gorgon]] [[Medusa (mythology)|Medusa]]. Hipparchus and Pliny made this a separate, though connected, constellation.<ref name="allen"/>
It is known as 大陵五 (the Fifth Star of the Mausoleum) in [[Chinese astronomy]], and also bore the grim name ''Tseih She'' 'Piled up corpses'.<ref name="allen"/>
===Astrology===
[[Astrology|Astrologically]], Algol is considered the most [[luck|unfortunate]] star in the sky.<ref name="allen"/> In the [[Middle Ages]] it was one of the 15 [[Behenian fixed stars|Behenian stars]],<ref>{{cite book
| first=Donald | last=Tyson | coauthors=Freake, James
| year=1993
| title=Three Books of Occult Philosophy
| publisher=Llewellyn Worldwide
| id=ISBN 0875428320 }}</ref> associated with the [[diamond]] and [[hellebore]], and marked with the [[kabbalistic]] sign: [[Image:Algol symbol (Agripe 1531).svg|75px]]
===Modern fiction===
[[Image:Algol.jpg|right|thumb|poster for ''[[Algol (film)|Algol]]'']]
One of the earliest films about alien invasion was a 1920 German silent film titled ''[[Algol (film)|Algol]]''. Renowned at the time for its sets, it featured [[Emil Jannings]] as Mephisto, an alien from Algol. All prints of the film were believed to have been lost,<ref name=FoSFF>{{cite book |title=Films of Science Fiction and Fantasy |author=Searles B|pages=p. 116-17|year=1988 |publisher=Harry N. Abrams |location=New York |isbn=0-8109-0922-7}}</ref> but an intact copy has been recovered.<!-- So saith the main article, unless that's deliberate vandalism. -->
*''[[The Hitchhiker's Guide to the Galaxy]]'' mentions Algol several times.
*The sci-fi comedy book ''[[Bikini Planet]]'' features aliens from Algol. They are a feminist society and all have lizard-like features.
* In the short story, ''[[Beyond the Wall of Sleep (short story)|Beyond the Wall of Sleep]]'', by [[H. P. Lovecraft]], a nova is mentioned as having taken place near Algol on February 22, 1901; this nova is, according to the story, the result of an epic space battle between two incorporeal beings, known in the story as the 'entity' and the 'oppressor.'
* In the [[Sega]] video game series [[Phantasy Star]], the star system which the series takes place in is called the [[Algol (Phantasy Star)|Algol Solar System]].
* [[Vintersorg]] has a song titled Algol on the album [[Cosmic Genesis]].
==References==
{{reflist}}
==External links==
* {{cite web | url = http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=Beta+Persei&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2006&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0 | title = HD 19356 -- Eclipsing binary of Algol type | publisher = SIMBAD| language = English | accessdate = 2006-07-31 }}
* {{cite web | date = January, 1999 | url = http://www.aavso.org/vstar/vsots/0199.shtml | title = Beta Persei (Algol) | publisher = AAVSO | language = English | accessdate = 2006-07-31 }}
* {{cite web | date = July 2005 | url = http://skyscript.co.uk/algol.html | title = The Horror-Scope of Algol | publisher = Skyscript | language = English | accessdate = 2006-07-31 }}
* {{cite web | url = http://www.solstation.com/stars2/algol3.htm | title = Algol 3 | publisher = SolStation | language = English | accessdate = 2006-07-31 }}
* {{cite web | date = 1998-03-04 | url = http://www.ari.uni-heidelberg.de/aricns/cnspages/4c02517.htm | title = 4C02517 | publisher = ARICNS | language = English | accessdate = 2006-07-31 }}
* {{cite web | url = http://www.alcyone.de/SIT/mainstars/SIT000666.htm | title = Algol | publisher = Alcyone ephemeris | language = English | accessdate = 2006-06-08 }}
* {{cite web | last = Kaler | first = Jim | url = http://www.astro.uiuc.edu/~kaler/sow/algol.html | title = Algol (Beta Persei) | publisher = Stars | language = English | accessdate = 2006-06-08 }}
* {{cite web | author = Bezza, Giuseppe [translated by Daria Dudziak] | url = http://www.cieloeterra.it/eng/eng.articoli.algol/eng.algol.html | title = Al-ghûl, the ogre. | publisher = Cielo e Terra | language = English | accessdate = 2006-06-08 }}
* [http://www.realmofalgol.wz.cz Czech space metal band "Realm of Algol"]
[[Category:Algol variables]]
[[Category:Arabic words and phrases]]
[[Category:Bayer objects|Persei, Beta]]
[[Category:B-type main sequence stars]]
[[Category:Flamsteed objects|Persei, 26]]
[[Category:HD and HDE objects|019356]]
[[Category:HIP objects|014576]]
[[Category:K-type subgiants]]
[[Category:Perseus constellation]]
[[Category:Stars with proper names]]
[[ar:رأس الغول]]
[[bg:Алгол (звезда)]]
[[cs:Algol]]
[[de:Algol (Stern)]]
[[el:Αλγκόλ]]
[[es:Algol]]
[[fr:Beta Persei]]
[[gl:Algol, estrela]]
[[ko:알골]]
[[hr:Algol (zvijezda)]]
[[it:Algol (astronomia)]]
[[lb:Algol (Stär)]]
[[nl:Algol (ster)]]
[[ja:アルゴル]]
[[pl:Algol (gwiazda)]]
[[pt:Beta Persei]]
[[ru:Алголь]]
[[sk:Algol]]
[[fi:Algol (tähti)]]
[[sv:Algol (stjärna)]]
[[tr:Umacı]]
[[uk:Алголь]]
[[zh:大陵五]]