Athena's Web Weekly Column

Week of May 11th, - May 17th, 2007

The Evil Eye

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  There are many stars in the sky, but there is only one that is known as "The Evil Eye."

The Evil Eye

The Evil Eye

  Beta Perseus, also called Algol, is an eclipsing variable found in the constellation of the legendary hero who rescued Andromeda. An eclipsing variable is actually two stars orbiting around each other. When the darker companion moves in a direct line between Algol and the Earth, Algol is eclipsed and it's light dimmed. Normally Algol's magnitude (a measure of how bright the star is) is 2.1. During an eclipse the brightness falls to 3.4. With stellar magnitudes, the lower the number, the brighter the image. The Sun and Moon, our brightest objects in the sky, have magnitudes in the negative numbers, as does Sirius, the brightest star in the sky.

  As with so many of the motions of heaven, the precision of its orbiting cycle has been closely monitored. Algol fades and rebrightens every 2.87 days, or every 68 hours and 49 minutes. Although it reaches its minima (faintest light) and remains there for approximately two hours, it takes another six for it to darken and then brighten again for a total of eight hours out of the total 69 hour period. For naked eye observations, two stars to compare are Gamma Andromedae (magnitude 2.1), to the west of Algol, and Epsilon Persei (magnitude 2.9) lying in the same constellation to its north. By comparing Algol's brightness with these two, one can tell when this infamous star is in its 'dark' period or not.

Medusa on a shield

Medusa's severed head

  The name of the star, Algol, comes from the Arabic "Al Ghul," which means the "Ghoul" or "Demon Star." This is the oldest known variable star and was thought to be the pulsing eye of the severed head of Medusa, the only mortal of the three Gorgon sisters. Arabic commanders knew never to attack during the "dark side" of Algol, as the resulting carnage inevitably turned out to be particularly pronounced.
Perseus

The constellation Perseus

The Hebrews knew Algol as "Rosh ha Sitan" or "Satan's Head," although they also thought of it as Lilith, the first wife of Adam before Eve was created. Thousands of miles away, the Chinese also were aware of Algol, and called it "Tseih She," which translates as "Piled up Corpses."

  Medusa was originally a priestess of Athena's, a name which means "Cunning One." Her sisters were Stheno ("Strong") and Euryale ("Wide Roaming"). Poseidon saw Medusa and raped her while she was in Athena's temple. Even though she tried to fight off the Water Lord's advances, Athena blamed the mortal and transformed Medusa and her sisters into hideous beasts with scaly skin, dragon's wings and hair formed of dozens of coiling snakes. Any who gazed upon Medusa were instantly turned to stone.

  This Wednesday, May 16th, the New Moon will align with Algol. Although the New Moon's at 3:27 PM, Algol will reach its minima at 2:12 the following morning.

  It will be interesting to watch to see how the dark phase of the Moon affects the dark phase of Algol. Since the New Moon influences not only the day upon which it occurs, but also the month following this lunation, let's watch to see how this thread impacts the days and weeks ahead. The New Moon is at 25 degrees and 33 minutes Taurus, while Algol's current position is 26 degrees and 12 minutes Taurus, or about two thirds of a degree out of exact, well within the limits defined for fixed stars.

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