Jimmy Westlake: Algol - the Demon Star

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Jimmy Westlake

Look for Algol, the Demon Star, in autumn's northeast sky during the early evening hours, just below the familiar W-shaped star pattern of Cassiopeia's Chair.

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.

Medusa met her death at the hands of the Greek hero Perseus, who was dispatched by the king to slay her and bring back the Gorgon's head. Armed with a magic sword, winged sandals, and a mirror-like shield, Perseus crept up on the slumbering Medusa in her lair. Watching only at her harmless reflection in his mirror-like shield, he severed her ugly head. He then used Medusa's head as a weapon in several battles, turning his foes into stone. The hero Perseus is immortalized in our autumn sky as a magnificent constellation. He is poised there in his winged sandals, victoriously holding his sword in one hand and the severed head of Medusa in the other.

The star that marks the eye of Medusa is a most remarkable star named Algol, meaning the "Demon Star." Every three days, the star Algol fades to one-third of its typical brightness for two hours and then returns to its original luster. It's as if Medusa is winking her evil eye at us!

Horrifying to early sky watchers, Algol's periodic winking no longer is a mystery. Algol is actually a pair of stars, almost in contact as they whirl around each other. When the fainter star eclipses the brighter star, Algol dims for a few hours. Algol was the first eclipsing binary star discovered and continues to be the most famous.

Look for the Demon Star below the familiar W-shaped pattern of Cassiopeia, high in the northeastern sky on autumn evenings. Algol will be in mid-eclipse at 4:30 a.m. Nov. 3, and then again every two days, 20 hours and 49 minutes thereafter. Start watching several hours before mid-eclipse, and then watch it slowly fade. Spooky!

While you are in the area, check out a couple of autumn's other celestial wonders, the Great Andromeda Galaxy and the Seven Sisters star cluster.

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published on the Web sites of CNN.com, NASA's "Astronomy Picture of the Day" Web site, Spaceweather.com, Space.com, Discover.com, MSNBC.com, NationalGeographic.com, and in Sky & Telescope, Astronomy, Night Sky, Discover, and WeatherWise magazines. His "Celestial News" article appears weekly in the Steamboat Pilot & Today. His "Cosmic Moment" radio spots can be heard on local radio station KFMU. Also, check out Jimmy's Web site at www.jwestlake.com.

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