Two sky tips for today. First, as Halloween approaches, try looking for the star Beta Persei, otherwise known as Algol in the constellation Perseus. This star’s proper name comes from the Arabic for head of the ghoul, or head of the demon. Second, have you been watching the moon lately? If so, you might know it’s almost the first quarter moon, to take place at on October 30, at 9:48 p.m. CDT in the central US. Some two hours later, the star Algol is predicted to be at its minimal brightness, at 11:52 p.m. CDT. Follow the links below to learn more about the moon and Mars – and the Ghoul Star!
Find the Ghoul Star of Perseus. Why did early stargazers name this star for a ghoul or demon? Beta Persei, otherwise known as the Ghoul Star, is known to vary in brightness over a regular time interval. The cycle lasts 2 days, 20 hours and 49 minutes. All the while, the star remains visible to the eye.
Algol’s brightness variations are not due to some special quality of a single star. In fact, this is a multiple star system, where one star regularly passes in front of another as seen from our earthly perspective.
When the dimmer of the two stars passes in front of the brighter, Algol shines at minimum brightness. The forecast calls for Algol to reach minimum brightness late tonight, on October 30 – at 11:52 p.m. CDT in the central U.S (that’s October 31 at 4:52 Universal Time).
Early stargazers had no way to know why Algol varied in brightness. But it’s likely that they did notice this star’s brightness change. Throughout parts of the ancient world, Algol was associated with demons or monsters. The Greeks and Romans identified the star with the Head of Medusa, a fearful monster with snakes in place of hair.
See the half-lit first quarter moon above the planet Mars in the south to southwest sky this evening. The illuminated side of the moon points toward the planet Mars, which shines as brilliantly as a 1st-magnitude star. As always, the lunar terminator – the shadow line dividing the lunar day from the lunar night – shows you where it’s sunrise on w waxing moon. If you have binoculars, check out the lunar terrain along the terminator, where the mixture of light and long shadows provides a wonderful, three-dimensional perspective to the lunar mountains, craters and valleys.
Bottom line: See the Ghoul Star, Beta Persei, around Halloween. Look for the moon and Mars at evening.
More Halloween adventures: