Halloween Star

StarDate: October 30, 2012

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To fans of the Batman movies and comic books, the name Ra’s al Ghul is well known. The character is a supervillain who’s intent on saving the planet through rather nasty means.

But the name didn’t originate with Batman. Instead, it was first given to a star in the constellation Perseus. The name means “the demon’s head.” It’s been shortened in modern times to just Algol — the demon — a name that seems appropriate for the Halloween time of year.

The star represents the head of Medusa, a snake-headed monster who was decapitated by Perseus. It may have gained that fearsome rep because for a few hours every three days or so, Algol’s brightness drops by more than two-thirds. For astute skywatchers, that big of a change is easy to see with the eye alone.

There’s nothing supernatural about Algol’s changing brightness, though. It’s all a matter of geometry.

Algol is a system of three stars. Two of them are separated from each other by just a few million miles. One of the stars is quite bright, while the other is much fainter. About every three days, the fainter star passes in front of the brighter one as seen from Earth, blocking much of the brighter star’s light, so the system fades dramatically. A few hours later, though, the eclipse ends and Algol returns to its usual bright glow.

But there is something a bit creepy going on with Algol — one star is consuming the other. We’ll save that part of the story for tomorrow — Halloween.

 

Script by Damond Benningfield, Copyright 2012

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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