December starwatch

All month long we can watch the changing shape of a triangle formed by Venus, Mars, and, low in the south, the lone bright star Fomalhaut in Piscis Austrinus, the southern fish.

With bright planets in both the morning and evening skies, December is a great time for fans of moon meetings.

On the first, a fingernail moon emerges from the sun’s afterglow in the company of Venus. Mercury is below the moon, but so near the sun as to be practically invisible. The next night, the moon and Venus again make a pair, and on the 3rd the moon hangs above the brilliant planet. Between the 4th and 5th, our peripatetic satellite sails above Mars. A new moon arrives at 12:53 a.m. on the 29th, and a thin crescent of the next cycle appears over the sunset horizon on the last evening of the year.

All month long we can watch the changing shape of a triangle formed by Venus, Mars, and, low in the south, the lone bright star Fomalhaut in Piscis Austrinus, the southern fish. Venus is now climbing toward Mars; early next year, the two will make a close approach and then separate as Venus again hurtles between Earth and the sun.

After reaching fullness in mid-month, the moon wanes as it continues its eastward march toward the rising sun. On the 22nd the moon and Jupiter ornament the morning sky. By the predawn hour, the moon’s fat crescent will be hanging above the giant planet high in the south, with Spica, the brightest star in Virgo, shining below Jupiter. Over the next few mornings, early birds can watch the crescent shrink as it plunges toward the southeast horizon.

December’s full moon arrives at 6:05 p.m. on Tuesday, the 13th. In most parts of Minnesota, this will be less than 90 minutes after moonrise, so it will be very round and beautiful. This moon is known, for obvious reasons, as the cold moon. Unfortunately, the night of the 13th-14th is the peak of the Geminid meteor shower, and the moon will wash out all but the brightest meteors. Brightness is a hallmark of the Geminids, however, so you may see some that night and for a few nights before and after. Meteors will radiate from near the Gemini twin Castor, in the knot of winter constellations now entering the evening sky from the east.

In the vanguard of those constellations is Taurus, the bull. The lovely Pleiades star cluster represents the bull’s shoulder, and below it is the V-shaped Hyades cluster, marking the bull’s face. The bright orangish star Aldebaran represents the bull’s eye, but isn’t part of the cluster. Be sure to use binoculars, especially with the Pleiades. At about 100 million years of age, these stars are quite young and some 440 million light-years away. The cluster contains many more stars than we can see, and it’s now gliding through dust that reflects its light and gives the visible stars a blue shimmer.

The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see:

Duluth, Marshall W. Alworth Planetarium: www.d.umn.edu/-planet

Twin Cities, Minnesota Institute for Astrophysics: www.astro.umn.edu/outreach/pubnight

Check out the astronomy programs at the University of Minnesota's Bell Museum ExploraDome: http://www.bellmuseum.umn.edu/exploradome

Find U of M astronomers and links to the world of astronomy at http://www.astro.umn.edu.

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