Stars over Sisters

December is a great month for stargazing.

There will be a lot going on that is worth seeing. Brilliant Jupiter, currently located in the constellation of Taurus, will dominate the evening sky and be visible all night. Now in Sagittarius, Mars is also an evening object, but positioned very low in the southwest and nearly lost in evening twilight.

As December begins, Venus and Saturn can be seen fairly close together in the eastern sky about an hour before sunrise, both in the constellation of Libra.

Meanwhile, the moon will darken during the first half of the month, reaching the new phase on December 13. Thereafter, the moon will brighten, becoming full by December 28.

The winter solstice begins at 3:12 a.m. PST on December 21. At that time winter will officially begin in the Northern Hemisphere, beginning with it the shortest day of the year.

Another exciting event, the Geminid meteor shower, will also occur during this month. Starting around December 6, we should be able to see one or two meteors per hour escaping from Gemini. But activity will pick up, and by December 13 we ought to see anywhere from 50 to 80 meteors per hour emanating from the constellation; by December 18 the shower will have ended.

Our main feature this month is the constellation Perseus. Perseus is the

24th-largest constellation and is bordered by Cassiopeia, Andromeda, Aries, Taurus and Auriga. The best time to see this constellation is around

9 p.m. Within the constellation are two fascinating objects: Algol, the demon star; and the double cluster.

Algol is actually an eclipsing double star system, though we see them as a single star. The two stars, which are extremely close together in space, orbit about each other very rapidly. Because this orbit is in the same plane as our line of sight from Earth, the two stars take turns moving in front of, then in back of, each other. This causes the star to fluctuate in brightness every two-and-a-half days. Ancient sky watchers believed the phenomenon was caused by demonic activity.

The double cluster consists of two separate clusters of stars, each one a beautiful object in its own right. Viewed together, however, they are a spectacular sight. The clusters are separated by thousands of light years, but in relation to everything else in the universe they are considered to be next-door neighbors. Although easy to locate with the naked eye, some optical assistance is needed to see the clusters in their full glory.

Perseus was one of the great heroes of Greek mythology. He was a demigod: the son of Zeus and the mortal Danae. His greatest triumph was defeating the gorgon Medusa. He was challenged to travel across the world and bring back the head of the hideous Medusa, a creature so vile that a single look in her eyes could turn even the strongest man to stone. With some help from the gods, a helmet, shield, and a magnificent jeweled sword, Perseus entered her lair and decapitated her, using her reflection in the shield to guide him. For his heroic deeds, when he died, Perseus was placed among the stars.

Algol represents the eye of Medusa and the double cluster marks the jeweled hilt of the sword.