Venus, Mars, and Jupiter have been around as evening stars for some time, though not as especially good ones. This month, as we approach and pass the winter solstice, evening planets will move well out ahead of the sun, and Venus and Mars will be more easily seen. Jupiter won't move accordingly, so we won't see it. Venus is bright enough to be seen low in the west any evening. Mars is much dimmer, but also higher, above and to Venus's left. Both improve their position in December, and Venus brightens. They make for a special sky on Christmas night, when the crescent moon joins them. The following events are in local time unless indicated otherwise.
Dec. 1: The moon is well up in the south at sundown, near the southern border of Pisces (with Cetus). Pegasus, four stars forming a great square, is above.
Dec. 4: Mercury begins retrograde motion. The gibbous moon tonight is in Aries.
Dec. 7-8: The reddish star below the moon is Aldebaran; Taurus's other stars are hidden by the moonglow. Full moon is at 5:53 Eastern standard time Saturday morning.
Dec. 8: Sunset tonight is the earliest of the year in the mid-northern latitudes. Later sunsets will be obvious in a week or so.
Dec. 9-10: The waning moon is in Gemini. The stars Pollux and Castor are to its left on the 9th, above it on the 10th.
Dec. 14: Mercury is in front of the sun at inferior conjunction and becomes a morning star.
Dec. 16-17: The waning gibbous moon, rising after midnight, introduces you to Spica, the bright star to its left on the 16th, closer to and below the moon on the 17th.
Dec. 19: Moonrise is about 3:45 this morning. The bright object below the crescent is Saturn.
Dec. 21: Winter begins in the Northern Hemisphere at 11:23 a.m. EST. This day (from sunrise to sunset) is the shortest of the year - 10 hours 13 minutes long at 30 north latitude; 9 hours 20 minutes at 40N; and 8 hours 4 minutes at 50N.
Dec. 22: New moon is at 6:47 a.m. EST, just a little past the winter solstice.
Dec. 23: The young crescent moon passes Jupiter, but they set about an hour or so after the sun.
Dec. 24: Mercury begins moving east again relative to the stars.
Dec. 25: The crescent moon joins Venus in the evening twilight sky, in the west from about half an hour after sunset till they set more than two hours later. Mars is higher, but much dimmer than Venus.
Dec. 26: Find Mars tonight close above the moon, still not very bright, but there's nothing around to compete with it except brilliant Venus, below and to the right.
Dec. 29-30: First quarter moon, just after midnight (12:27 a.m. EST) on the 30th, is in the constellation Cetus.
Dec. 31: Tonight the moon is safely in the Zodiac again, moving from Pisces into Aries near their junction with Cetus.