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The Demon Star Winks This Month (2017)

The Demon Star Winks This Month (2017)

As we have just passed Halloween, it’s interesting to note that in a night sky where a variety of strange beasts and creatures proliferate, there are no witches, ghosts, or even a creepy spider that are recognized constellations. But we do have a gorgon — or at least the head of one — visible in the northeast part of the sky. The gorgon is Medusa, who had snakes for hair and was so hideous that if you looked at her you would instantly turn to stone.

The Star Algol – Medusa’s Eye
Now in our evening sky, ascending in the northeast, is Perseus, the Hero (you might recognize the name from the “Perseid” meteor shower we enjoy each August). Perseus slayed Medusa by beheading her with his sword. In the sky, Perseus is holding Medusa’s severed head, and one of Medusa’s eyes is marked by the star Algol, and has been known since ancient times as “The Demon Star” and is one of the most famous variable stars in the sky. Its very name, from the Arabic Al Ra’s al Ghul, means “The Demon’s Head” and ancient astrologers considered Algol the most dangerous and unfortunate star in the heavens.

This seems to suggest that the medieval stargazers were aware of its ability to mysteriously change in brightness. In 1782, amateur astronomer John Goodricke realized that this star was really a pair of stars orbiting a common center of gravity, and that when the dimmer of the two crossed in front of the other, like an eclipse, the light from Algol appeared to fade, thus it appears to wink.

Because the entire eclipse takes 9 hours and 40 minutes from start to finish, the entire performance can be seen in a single night when the timing is right. This stellar eclipse occurs like clockwork at intervals of 68 hours, 48 minutes and 56.5 seconds.

Below is a timetable for when Algol will be at minimum brightness during November for various time zones:

November 2:
3:38 a.m. EDT
2:38 a.m. CDT
1:38 a.m. MDT
12:38 a.m. PDT

November 5:
12:27 a.m. EST
11:27 p.m. (Nov. 4) CST
10:27 p.m. (Nov. 4) MST
9:27 p.m. (Nov. 4) PST

November 7:
9:16 p.m. EST
8:16 p.m. CST
7:16 p.m. MST
6:16 p.m. PST

Normally, Algol appears 3.3 times brighter than during the peak of the eclipse; at its brightest it shines as bright as magnitude +2.1 and at its dimmest it has faded to +3.4. Two hours before the predicted minimum start checking Algol’s brightness. It is at minimum light for about 20 minutes – as the large, dim star passes across the smaller, brighter one – then it gradually returns to normal.

Animation of an eclipsing binary star.

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