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Astronomy: December Observing Highlights

12-2-11 Winter Night Dane VanderLee
A bright planet on a cold winter night. Credit: Dane VanderLee

December hosts more hours of darkness than any other month. This is because the solstice occurs just after midmonth. On December 21 for those in the Central Time Zone and to the west and just after midnight on December 22 for those in the Eastern Time Zone, the solstice occurs. This is the moment that Earth’s northern axis tilts as far away from the sun as it gets.

All these extra hours of darkness, not to mention the coming cold of winter, makes people want to curl up inside by a fire and read a good book. But if you can brave the cold dark nights, you can see some beautiful astronomical delights.

The two brightest planets, Jupiter and Venus, are taking up residence in the evening sky. They are not hard to miss. Look for an unmistakably bright point of light in the west after sunset; that will be Venus. The bright beacon climbing high in the east-southeast is Jupiter.

The winter constellations, most notably the grand Orion, are also appearing in the east during mid-evening. The full moon of December is called the Cold Moon, which occurs on December 10 this year. A total lunar eclipse will also occur on that date, which will require early morning viewing for those of us in North America. See more about the eclipse in next week’s blog.

Two annual meteor showers occur in December, with the Geminids on December 13 being one of the best of the year with 80 meteors an hour possible. A waning moon will interfere with the show, however. The Ursids is the second shower, occurring on December 22, but it only provides about 9 meteors an hour at maximum.

Annual meteor showers are created by Earth passing through the debris trail of comets. But the Geminids is unusual in that the space object that left behind the debris trail was an asteroid known as 3200 Phaethon. Recent research has bolstered the evidence that Phaethon is related to asteroid belt inhabitants such as Pallas, one of the largest known asteroids. Phaethon’s composition is significantly similar, but Phaethon is a rebellious child, sometimes acting comet-like.

For more on this month's observing, see The Night Sky Guide for December 2011.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.

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