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The star Algol is a good one for Halloween. It’s in the northeast as night falls, and climbs directly overhead in the wee hours of the morning. More important, though, is its name: “Algol” comes from the Arabic phrase “ras al-ghul” — the head of the demon.

Ancient skywatchers may have bestowed the name because Algol does something spooky: It fades and brightens over a period of about three days. And the change is obvious even to the unaided eye — something you can’t say for any other star.

It took a long time to figure out why that happens. It turns out that the system contains two stars in a tight orbit around each other. They line up so that, as seen from Earth, they eclipse each other. When the fainter star passes in front of the brighter one, the system fades to just a third of its un-eclipsed brightness.

Algol actually has a third star. But it’s so far away from the others that it doesn’t line up in a way that causes eclipses.

A study released a year ago said there could be as many as four more stars in the system. A scientist in Finland used a complicated mathematical model to simulate the motions of the known stars. The model suggested they could be tugged by the gravity of stars that take anywhere from a couple of years to a couple of hundred years to orbit them. But so far, no one has seen any other stars at Algol — a “demonic” star system for Halloween.

We’ll have more about Halloween tomorrow.

Script by Damond Benningfield

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