The smallest and largest of the Sun’s major planets will stage a relatively rare encounter this month as they pass each other in the dawn twilight. Jupiter should be easy to see, but Mercury could take some work. The great Winter Circle climbs higher each night, and is in good view by 8 p.m. by month’s end. It consists of seven bright stars encircling orange Betelgeuse, the shoulder of Orion.
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In the Sky This Month
December 10: Stretching Out
Eridanus, the river, meanders across the southern sky at this time of year. It is one of the largest constellations, stretching almost 60 degrees. Its northern end is northwest of Rigel, the brightest star in Orion.
December 11: Gemini
The constellation Gemini is in good view by about 8 p.m. It is best known for Castor and Pollux, the two bright stars that represent the heads of the twins. They are low in the east-northeast at that hour, with Castor above Pollux.
December 12: Dusty Display
The Geminid meteor shower is expected to be at its best over the next couple of nights. And the Moon sets early enough that it will allow the meteors to shine through. The shower is spawned by an asteroid, which sheds dust grains as it orbits the Sun.
December 13: Comet Wirtanen
Comet Wirtanen is streaking across Taurus, which is in the east at nightfall. It will pass between the bull’s “eye” — the star Aldebaran — and shoulder — the Pleiades star cluster. Under dark skies, the comet may be bright enough to see with the eye alone.
December 14: Moon and Mars
Mars is in great view tonight. The Red Planet looks like a bright orange star just above the Moon as night falls. It will stand farther to the right of the Moon tomorrow evening.
December 15: Auriga
Auriga is low in the east-northeast as night falls and climbs high across the sky later. It is marked by a pentagon of stars. It’s easy to pick out thanks to the brightest member of that figure, Capella, which is one of the brightest stars in the night sky.
December 16: Messier 37
Messier 37, a 500 million-year-old star cluster, climbs high overhead during the night. It’s not quite visible to the unaided eye, but it’s a fairly easy target for binoculars. It probably is about 5,000 light-years away, and contains about 500 known stars.