[[Image:Position Beta.png|thumb|right|250px|Location of Algol (Beta Persei) in the constellation of Perseus.]]
'''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 know 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 in History==
The Algol star system was know known at least since antiquity. The [[Ancient Greeks]] called Algol the "Evil eye" of [[Medusa]], this . 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 this 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>
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|Europeans]] 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">http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Perseus*.html</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 has had some dark spot.<ref>http://www.surveyor.in-berlin.de/himmel/Bios/Goodricke-e.html</ref> It wasn't until 1881, when 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>
==Star System==
===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, its 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 km/sec and could possibly be less then 300 million years old.
===Beta Persei B===
The '''Algol paradox''' came about because according to the theory of [[Stellar Evolution|stellar evolution]], stars in a binary star system form at about the same time, and the more massive star will evolve more quickly then the less massive one. The paradox is a result of Algol A being more massive star of the binary pair, yet still a main sequence star, while the less massive Algol B has already reached the subgiant stage in its evolution.
Astronomers believe the paradox is explained though Algol B losing much of its [[mass]]. As Algol B swelled up into the subgiant stage, its companion star, being so close, would produce [[tide|tides]] in Algol B. Matter from Algol B's now swollen outer shell exceeded its '''Roche lobe''' (the volume where the star's gas is gravitationally bound). These outer gases would then be pulled away by the tidal forces into an accretion stream of matter that moves towards Algol A, giving Algol B a teardrop shape pointing towards its companion. The As a result Algol B is losing mass at some two hundred millionths of a solar mass a year. Over time, the once massive star been reduced to 79 percent of the Sun's mass.<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1995BaltA...4...64P</ref>
[[Category:Astronomy]]