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December Starwatch

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December's deep, dark nights may be cold, but they generate ideal conditions for viewing the stars.

This year we also get a shot at seeing a major meteor shower and a rare chance to ring out the old year under a full moon.

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The Geminid meteor shower peaks the evening of the 13th, spewing fireballs from a point near the Gemini twin Castor. This point, called the radiant, will be well up in the east by mid-evening and visible all night.

Gemini belongs to the knot of familiar winter constellations making their grand entrance over the eastern horizon this month.

Orion, with his trademark belt and sword, stands out from the pack. Following at his heels, Sirius, the Dog Star, outshines everything but the moon and the brighter planets.

A beacon in the southwest, Jupiter comes out after sunset and sinks lower every night. In the morning sky, Venus plummets and is lost in the sun's foreglow. Saturn, high in the south at dawn, slowly brightens and opens its rings.

Look for it between the tail of Leo and bright Spica in Virgo.

But if you must choose one planet to watch this month, make it Mars.

The Red Planet rises in the east behind Gemini, about five hours after sunset on the 1st and less than three hours by the 31st. During December its brightness doubles, and viewers with good telescopes may be able to pick out surface features like the shrinking north polar ice cap.

Mars owes its growing prominence to Earth, which is catching up to it in the orbital race and will pass it in late January.

If it's still hard to find, look at the predawn sky on the 6th; Mars will shine between a fat waning moon to the west and the bright star Regulus, in Leo, to the east.

And around 10:30 p.m. that evening, Mars and the moon will appear together above the eastern horizon.

Winter arrives officially at 11:47 a.m. on the 21st, when the sun dips to a point directly over the Tropic of Capricorn. On that day the Twin Cities area will enjoy just eight hours and 47 minutes of daylight.

The day length diminishes with increasing distance north; Duluth, for example, gets 15 minutes less. The good news: The earliest sunset comes sometime (the exact day varies by latitude) during the second week of December.

After that, sunsets start coming later, and by month's end we'll see 10 more minutes of light at the close of day.

And speaking of light, we get two full moons this month. The full Cold Moon comes on the 2nd, at 1:30 a.m., while the full Long Nights Moon falls on New Year's Eve.

Recently, the second of two full moons in a month has been called a blue moon, but reports in the popular astronomical literature have labeled this an error based on a misinterpretation of information in the 1937 Maine Farmer's Almanac.

A blue moon is really supposed to mean the third of four full moons when four fall in a season.

So does our New Year's Eve moon qualify? Since it's only the first full moon of the winter season, obviously not.

On the other hand, ideas change, names change, and "blue moon" has been widely interpreted as the second of two full moons in a month.

Besides, as the second brightest and last full moon of 2009 - not to mention that it ushers in the last year of the decade - the New Year's Eve moon deserves a little recognition.

The University of Minnesota offers public viewings of the night sky at its Duluth campus.

For more information and viewing schedules, visit the Marshall W. Alworth Planetarium at www.d.umn.edu/~planet. Contact Deane Morrison at (612) 624-2346 or morri029@umn.edu.

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