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TOPIC: Algol


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RE: Algol
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Algol, The "Demon Star"
Algol, the second brightest star in the northern constellation Perseus, is a beautiful example of an eclipsing variable star. While the ancients were frightened by Algol its name comes from the Arabic "al Ghul" meaning "The Demon" it's a beautiful example of two stars revolving about each other in a rhythmic gravitational dance. And you can see it from your backyard. No telescope required.

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Algol the Demon Star
Hollywood has created some scary monsters for us, but Hollywood has nothing on ancient Greece. Some of the monsters passed down to us through Greek mythology are as terrifying as anything ever conjured up by the human imagination.
To me, the most chilling monster of them all is the Gorgon sister known as Medusa. At one time, Medusa was a beautiful young woman with long, flowing hair. Many suitors pursued her, trying to win her hand in marriage. Then, one day, while Medusa prayed in the temple of Athena, Poseidon, the Greek god of the sea, entered the temple and ravished her. Athena was furious that her temple would be so violated. She transformed the lovely Medusa into a hideous monster, changing her beautiful hair into a writhing tangle of hissing snakes and proclaiming that any man who gazed into her eyes would be turned into solid stone.

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Algol (Beta Persei) will be at minimum at 01:36 UT, 17th October, 2006, (magnitude 3.4) and will take about five hours to return to its normal brightness (magnitude 2.1).

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Algol (beta Persei), is predicted to be at minimum at 01:35 on Monday January 9th, 22:30 on Wednesday 11th, and 19:20 on Saturday 14th.
On each occasion, when the fainter secondary component passes in front of the brighter primary, the star takes a few hours to dim from magnitude 2.1 to 3.4 (easily detectable by the naked eye), and a few more to return to normal.

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Algol, (Beta Persei), in the constellation Perseus is nearly overhead at around 10:30 p.m. local time.

Algol is an eclipsing binary system.
The light from Algol appeared to fade every 68 hours 48 minutes and 56 seconds.
Medieval Arabs were aware of its marked changes in brightness, and assigned it the name "Demon Star". The word "ghoul" comes from the same Arabic word.
To the Ancient Greeks, Algol was the "Head of Gorgon Medusa".
The Chinese gave it the gruesome title Tseih She, the "Piled-up Corpses".


Position(2000): RA = 03h 08m 10.13s Dec= +40 57' 20.3"

In 1782, amateur astronomer John Goodricke realised that the star was really a pair of stars orbiting a common centre of gravity. When the dimmer of the two crossed in front of the other, the light from Algol appeared to fade.


A blue spectral class B8 star with a diameter of 3 solar diameters and red-yellow spectral class K2 star of about 3.5 solar diameters are in very close orbit around each other . There are indications that Algol system contains at least one other star, quite distant from the other two, and orbiting them in a little under two years. There is also evidence for as many as three other companions, which would make Algol a sextuple star system.

Algol lies some 93 light years (28 parsecs) from the Earth. When not eclipsed by its companion, its magnitude of +2.1 makes it the second brightest of the stars in the constellation of Perseus.

On the night of November 26-27, observers across much of North America and throughout Europe will be in perfect position to watch Algol undergo its eclipse. Most of the time the star's light appears constant, but for about four hours its light varies noticeably. At its minimum brightness Algol appears only about one-third as bright as normal.

It is and ideal target for Amateurs, because the entire eclipse takes 9 hours and 40 minutes from start to finish, the entire eclipse can be seen in a single night.
November/December is the ideal time.



Algol will be at minimum at 1:25 GMT on November 27, ideally placed for Europeans.
Check Algol's brightness, against nearby stars, a couple of hours before the predicted minimum. It is at minimum light for a 20-minute period, as the large, dim star passes directly in front of the smaller, brighter companion.

There are several opportunities to see Algol undergo an eclipse during December.
For the Americas, it will be at minimum on December 14 at 1:20 a.m. EST and on December 16 at 10:09 p.m. EST (7:09 p.m. PST).

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