Changes

| image          =Position Beta.png

| image          =Position Beta.png

| designation    =Beta Persei

| designation    =Beta Persei

| rightascension  =03^h 08^m 10.1315^s  

| rightascension  =03^h 08^m 10.1315^s<ref name=simbad>[https://simbad.u-strasbg.fr/simbad/sim-id?Ident=algol&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id Algol] from the [http://simbad.u-strasbg.fr/simbad SIMBAD Astronomical Database]</ref>

| declination    =+40^o 57′ 20.332″

| declination    =+40° 57′ 20.332″<ref name=simbad/>

| distance        =93 ±2 ly

| distance        =92.8 ly<ref name=constellation-guide>{{cite web|url=https://www.constellation-guide.com/constellation-list/perseus-constellation/|title=Perseus Constellation|accessdate=2019-03-27}}</ref>

| constellation  =Perseus

| constellation  =Perseus

| type            =Binary star

| type            =Binary star

| dimensions      =

| dimensions      =

| magnitude      =Absolute Mag: -0.15<br/>Apparent Mag: 2.12

| magnitude      =Apparent Mag: +2.12<ref name=constellation-guide/><br/>Absolute Mag: -0.15<ref name=constellation-guide/>

| redshift        =

| redshift        =

| radvelocity    =3.7 km/s

| radvelocity    =4.0±0.9 km/s<ref name=simbad/>

| propmotion      =RA: 2.39 mas/yr<br/>Dec.: -1.44 mas/yr

| propmotion      =RA: 2.99 mas/yr<ref name=simbad/><br/>Dec.: -1.66 mas/yr<ref name=simbad/>

| parallax        =35.14 ±0.90 mas

| parallax        =36.27±1.40 mas<ref name=simbad/>

}}

}}

'''Algol''', also known as '''Beta Persei''', is a triple star system located 92.8 light years away in the constellation of [[Perseus]]. A star system that has been well known throughout [[human history]], it is also the first and most well known eclipsing binary. Normally Algol's apparent magnitude is 2.1, but every 2 days, 20 hours, and 49 minutes, the magnitude drops to 3.4 for some 10 hours. This is due to Algol A (Beta Persei A) being regularly eclipsed from our point of view, by the dimmer Algol B (Beta Persei B).<ref>http://csep10.phys.utk.edu/astr162/lect/binaries/algol.html</ref>

'''Algol''', also known as '''Beta Persei''', is a triple star system located 92.8 light years away in the constellation of [[Perseus]].<ref name=constellation-guide/> A star system that has been well known throughout [[human history]], it is also the first and most well known eclipsing binary. Normally Algol's apparent magnitude is 2.1, but every 2 days, 20 hours, and 49 minutes, the magnitude drops to 3.4 for some 10 hours. This is due to Algol A (Beta Persei A) being regularly eclipsed from our point of view, by the dimmer Algol B (Beta Persei B), making it a type of [[variable star]].<ref name=constellation-guide/>

==Algol in History==

==Algol in History==

The Algol star system was known at least since antiquity. The [[Ancient Greeks]] called Algol the "Evil eye" of [[Medusa]].  This was most likely due to the regular occurrences of the change in brightness and color as Beta Persei B eclipsed Beta Persei A. The name Algol itself is derived from the [[Arabic]] term أس الغول ''ra's al-ghūl'', meaning the Demon's Head or the Head of the Ogre. The name likely stems from the [[Greek]] view of the star system, specifically [[Ptolemy]], who named it as ''τῶν ἐν γοργονίῳº ὁ λαμπρός'', meaning "the bright one of those in the [[Gorgon|Gorgon's]] head". The names "Blinking Demon" and "Demon Star" are [[English]] translations of the Arabic name.<ref>Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning (revised edition). Dover. pp. 332–33. ISBN 0-486-21079-0. OCLC 185804232 637940</ref>

The Algol star system was known at least since antiquity. The [[Ancient Greeks]] called Algol the "Evil eye" of [[Medusa]].  This was most likely due to the regular occurrences of the change in brightness and color as Beta Persei B eclipsed Beta Persei A. The name Algol itself is derived from the [[Arabic]] term أس الغول ''ra's al-ghūl'', meaning the Demon's Head or the Head of the Ogre. The name likely stems from the [[Greek]] view of the star system, specifically [[Ptolemy]], who named it as ''τῶν ἐν γοργονίῳº ὁ λαμπρός'', meaning "the bright one of those in the [[Gorgon|Gorgon's]] head". The names "Blinking Demon" and "Demon Star" are [[English]] translations of the Arabic name.<ref name="penelope">Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning (revised edition). Dover. pp. 332–33. ISBN 0-486-21079-0. OCLC 185804232 637940 Avaliable online at [http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Perseus*.html penelope.uchicago.edu]</ref>

In [[Hebrew]] legend, the star was seen as ''Rōsh ha Sāṭān'' or '[[Satan|Satan's]] head'. It was also linked with the mythical [[Lilith]]. In Latin it was called ''Caput Larvae'', or 'Spectre's Head'.<ref name="penelope">http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Perseus*.html</ref> [[Medieval]] [[Europe]]ans saw Algol as one of the 15 Behenian stars used for [[astrology]].<ref>Tyson, Donald; Freake, James (1993). Three Books of Occult Philosophy. Llewellyn Worldwide. ISBN 0875428320. OCLC 26634250 41597186</ref> The [[Chinese]] named the star 大陵五, meaning the Fifth Star of the Mausoleum, although they also named it 叠尸 or ''Tseih She'', meaning 'Piled up corpses'.<ref name="penelope"/>

In [[Hebrew]] legend, the star was seen as ''Rōsh ha Sāṭān'' or '[[Satan|Satan's]] head'. It was also linked with the mythical [[Lilith]]. In Latin it was called ''Caput Larvae'', or 'Spectre's Head'.<ref name="penelope"/> [[Medieval]] [[Europe]]ans saw Algol as one of the 15 Behenian stars used for [[astrology]].<ref>Tyson, Donald; Freake, James (1993). Three Books of Occult Philosophy. Llewellyn Worldwide. ISBN 0875428320. OCLC 26634250 41597186</ref> The [[Chinese]] named the star 大陵五, meaning the Fifth Star of the Mausoleum, although they also named it 叠尸 or ''Tseih She'', meaning 'Piled up corpses'.<ref name="penelope"/>

The first known recording of Algol's regular variation in its magnitude was in 1667 by Geminiano Montanari. In May 1783, John Goodricke presented his findings on the proposed cause of Algol's variability to the Royal Society. He believed a dark body regularly passed in front of the star, or that the star itself had some dark spot.<ref>http://www.surveyor.in-berlin.de/himmel/Bios/Goodricke-e.html</ref> It wasn't until 1881, that Edward Pickering, an astronomer from [[Harvard]], brought forth evidence that Algol was an eclipsing binary star system.<ref>http://adsabs.harvard.edu/abs/1881AReg...19..253.</ref> This was confirmed in 1889 by Hermann Carl Vogel, who discovered periodic [[Dopper Shift|Doppler shifts]] in the spectrum of Algol A and the eclipsing Algol B.<ref>http://adsabs.harvard.edu/abs/1989SSRv...50....1B</ref>

The first known recording of Algol's regular variation in its magnitude was in 1667 by Geminiano Montanari. In May 1783, John Goodricke presented his findings on the proposed cause of Algol's variability to the Royal Society. He believed a dark body regularly passed in front of the star, or that the star itself had some dark spot.<ref>{{cite web|url=http://www.surveyor.in-berlin.de/himmel/Bios/Goodricke-e.html|title=John Goodricke - The Discovery of the Occultating Variable Stars|accessdate=2019-03-27}}</ref> It wasn't until 1881, that Edward Pickering, an astronomer from [[Harvard]], brought forth evidence that Algol was an eclipsing binary star system.<ref>Pickering, E. (1881). Reviews. ''Astronomical register'', 19, pp.253-256. [https://ui.adsabs.harvard.edu/#abs/1881AReg...19..253./abstract Bibcode:1881AReg...19..253.]</ref> This was confirmed in 1889 by Hermann Carl Vogel, who discovered periodic [[Doppler effect|Doppler shifts]] in the spectrum of Algol A and the eclipsing Algol B.<ref>Batten, A. (1989). Two centuries of study of Algol systems. ''Space Science Reviews'', 50(1-2), pp.1-8. [https://ui.adsabs.harvard.edu/#abs/1989SSRv...50....1B/abstract Bibcode:1989SSRv...50....1B]</ref>

==Star System==

==Star System==

Algol is a triple star system. The first two [[star]]s make up the famous eclipsing binary and are separated from each other by a distance of only 0.062 AU. The orbit of the two stars is highly circular and take only 2.87 days to complete. From [[Earth]], the orbit is inclined at 97.69°.<ref>http://adsabs.harvard.edu/abs/1996AAS...188.6014M</ref> A third star orbits the first two at the distance of 2.69 AU, taking some 1.86 years to complete with an inclination of 83.98°.<ref>http://ad.usno.navy.mil/wds/orb6.html</ref>

Algol is a triple star system. The first two [[star]]s make up the famous eclipsing binary and are separated from each other by a distance of only 0.062 AU. The orbit of the two stars is highly circular and take only 2.87 days to complete. From [[Earth]], the orbit is inclined at 97.69°.<ref>Molnar, L. and Mutel, R. (1996). Dynamical Evolution of the Algol Triple System. ''Bulletin of the American Astronomical Society'', 28, p.291. [https://ui.adsabs.harvard.edu/#abs/1996AAS...188.6014M/abstract Bibcode:1996AAS...188.6014M]</ref> A third star orbits the first two at the distance of 2.69 AU, taking some 1.86 years to complete with an inclination of 83.98°.<ref name="kim">Kim, H. (1989). BV light curve analysis of Algol. ''The Astrophysical Journal'', 342, p.1061. [https://ui.adsabs.harvard.edu/#abs/1989ApJ...342.1061K/abstract Bibcode:1989ApJ...342.1061K]</ref>

===Beta Persei A===

===Beta Persei A===

'''Algol A''' (Beta Persei A) is a blue white main sequence dwarf star of spectral type B5-8 V, and the most massive of the triple star system. The star has a diameter 2.88 times that of our [[Sun]] with a mass 3.59 times as great.<ref name="kim">http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1989ApJ...342.1061K</ref> The star is considerably brighter than the Sun. Its visual luminosity is 98 times of the Sun, and the total luminosity though is some 200 times as great, accounting for [[ultraviolet]] [[radiation]]. Algol A rotates at a quick 65&nbsp;km/sec and could possibly be less than 300 million years old.

'''Algol A''' (Beta Persei A) is a blue white main sequence dwarf star of spectral type B5-8 V, and the most massive of the triple star system. The star has a diameter 2.88 times that of our [[Sun]] with a mass 3.59 times as great.<ref name="kim"/> The star is considerably brighter than the Sun. Its visual luminosity is 98 times of the Sun, and the total luminosity though is some 200 times as great, accounting for [[ultraviolet]] [[radiation]]. Algol A rotates at a quick 65&nbsp;km/sec and could possibly be less than 300 million years old.

===Beta Persei B===

===Beta Persei B===

For an [[terrestrial planet|Earth-like]] world to have liquid [[water]] on its surface, it would have to be around 14 AU from the three stars, or the equivalent of an orbit between [[Saturn]] and [[Uranus]]. The hypothetical world would have an orbital period of over 27 years. Because the system itself is very young, it is unlikely such a planet would have time to cool to the point of holding water.

For an [[terrestrial planet|Earth-like]] world to have liquid [[water]] on its surface, it would have to be around 14 AU from the three stars, or the equivalent of an orbit between [[Saturn]] and [[Uranus]]. The hypothetical world would have an orbital period of over 27 years. Because the system itself is very young, it is unlikely such a planet would have time to cool to the point of holding water.

==References==

==References==

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