December 2005

by Deane Morrison

Like a seasoned performer, Venus saves its climactic performance for the end. In December, as our sister planet prepares to drop out of the sky and hurtle between Earth and the sun, it reaches maximum height and brilliance for its current stint as an evening "star." Telescopic viewers will be treated to the spectacle of a steadily thinning and lengthening crescent; if you have only binoculars, try to find Venus before or at sunset in order to make out its crescent shape. On the 4th, a crescent moon appears just below and slightly left of Venus, which will help locate the planet during daylight hours.

Mercury makes a nice morning appearance, especially during the first week of the month. About an hour before sunrise, Mercury will be in the east-southeast, near the horizon to the lower left of Jupiter. The planets form an almost straight line with the bright star Spica in Virgo, which appears to the upper right of Jupiter. Mars, still striking, is well up in the east at sunset, and Saturn rises in mid-evening. Between Mars and Saturn are the winter constellations Taurus, Orion, Gemini, Auriga, Canis Major and Canis Minor. Rising on the heels of its more spectacular cousins comes dim Cancer, harboring what may be the loveliest spectacle of the season: the Beehive star cluster with Saturn inching toward it from the east.

The full moon of December, called the cold moon or the long nights moon by Algonquin Indians, occurs after moonset the morning of the 15th, so enjoy it the night before. Ten days later, at 7:33 a.m. CST -- about 15 minutes before sunrise -- on Christmas morning, the waning moon's bright edge blots out Spica. Spica will reappear behind the moon's dark edge more than an hour later, but by that time the sun will have long since risen.

The sun dips to a point over the Tropic of Capricorn at the winter solstice, which happens at 12:35 p.m. CST on the 21st. This is, of course, the shortest day of the year in the Northern Hemisphere. But it is not the day of the earliest sunset or the latest sunrise. Earliest sunset occurs on the 9th near the Twin Cities, later for more northern latitudes, and the latest sunrise doesn't arrive until early January. Since most people experience sunset more keenly than sunrise, the phenomenon of later sunsets each night after mid-December may give the impression that days are lengthening more than they really are.

If you're lucky enough to live under dark skies far from city lights, December is truly a winter wonderland. Almost directly overhead this month is Perseus with its crown jewel, the blinking star Algol. Algol is a multistar system, and as one star passes in front of another, it eclipses its companion and we see a dimming of Algol. Its brightness waxes and wanes every couple of days, so a stretch of clear moonless nights may allow you to catch it in the act. Algol represents the eye of the Gorgon Medusa, whom Perseus slew, and its name comes from the Arabic for "demon."

The Geminid meteors fly in late evening on the 13th. Typically bright and fast, Geminids radiate from a point near the head of the Gemini twin Castor. Unfortunately, this year a nearly full moon will interfere with all but the brightest meteors.