Starwatch: Ornaments decorate the December sky
December's skies start to fill with ornaments, as planets rise ahead of the morning sun, the moon conducts its monthly tour of the sky, and the bright winter stars make their annual grand entrance.
Early risers will see Venus in the southeast. Look an hour before sunrise on the 3rd and 4th to see a waning crescent moon hanging near the planet.
On the 5th, a scrawny old moon appears well below Venus, close to the east-southeast horizon.
On the 31st, you may catch another waning moon, Venus and Jupiter lined up top-to-bottom in that order.
Mercury makes a brief foray into the morning sky. Look close above the southeast horizon about 45 minutes before sunrise between the 10th and 12th.
On the 21st, Mercury and Jupiter pass each other as the little planet drops out of the sky and the big one climbs into it.
Above all this lunar and planetary action shines Arcturus, the anchor of kite-shaped Bootes, the herdsman.
In the evening, Mars holds its own in the south to southwest, floating through the water constellations Aquarius and Pisces. Watch it glide below the Circlet of Pisces during the fourth week of the month. The Circlet is right beneath the Great Square of Pegasus, a dominating presence in the autumn and early-winter sky.
To the east, the winter constellations are moving into prominence. The Pleiades star cluster is well up at nightfall, while below it, the V-shaped Hyades cluster and the bright orangish star Aldebaran mark the face of Taurus, the bull. The bull's horns extend far to the east.
The star at the tip of the higher horn belongs officially to Taurus, but most star charts also include it in the constellation Auriga, the charioteer. Auriga's brightest star, Capella, is the brilliant beacon in the northeast after nightfall.
December's full moon arrives on the 22nd. It rises after sunset and travels the night sky among the stars of Gemini. Its berth that night is about midway between Capella and Sirius, the brightest of all stars (excluding the sun, of course).
Winter begins with the solstice at 4:23 p.m. on the 21st, when the sun reaches a point over the Tropic of Capricorn. At that moment, an observer in space would see the Earth lighted from the Arctic Circle down to the South Pole and up to the Antarctic Circle on the dark side of the planet.
The day of the winter solstice is always short and usually cold, but remember that by then the sun will have begun setting later each day.
Minnesota Starwatch is a newsletter describing the night sky in the Midwest. Updated monthly, it is produced by Deane Morrison, University of Minnesota Institute for Astrophysics. Find U of M astronomers and links to the world of astronomy at astro.umn.edu.