The months of December through February are the cloudiestof the year, averaging only about 30% of possible sun, and star light. Needless to say, clear nights in December should be cherished, especially considering the sights to be seen and the fact that December brings the longest nights of the year, which allows for some unique fun. Only at this time of year is it possible to observe something twice on the same night: once on the set in the evening and again on the rise in the morning. Vega and Deneb, two bright stars of the Summer Triangle, make great targets for this once a year opportunity. I've done it, you should, too. On to constellations, December allows for observation of the sky for three quarters of the year. Take a last look at the fall constellations as the sun sets, probe the winter constellations in the dead of night, and race the light to behold the spring constellations as dawn nears. There's way too much to be seen for going into detail here, so grab your sky atlas and some warm clothing to prepare for an all night observing session that will take you through the majority of the year. As two last planetary notes, keep an eye on Mars, it will nearly double in brightness by the end of the month. Want to see Neptune? Look near Jupiter. This is the way Galileo saw it 400 years ago.
December Visual Observing Highlights
Early December: Jupiter emerges due South at twilight, no better time for telescopic observation. Also be sure to catch Venus at dawn low, extremely low, on the Southeastern horizon.
December 1: The full moon splits the sky between the Pleiades and Hyades
December 5: The waning gibbeous moon, Pollux, and Castor line up.
December 6: The moon is within 5 degrees of the Beehive Cluster. Use binoculars.
December 7: Cosmic triangle: Regulus, moon, Mars. Grab the camera. Earliest sunset of the year.
December 13/14: Geminid Meteors peak. Keep an eye to the sky about a week either side of this date.
December 18: The moon meets Mercury low in the Southwest. Test your horizon.
December 21: Winter Solstice, the longest night of the year.
December 28: The waxing gibbeous moon scrapes the Pleiades
December 31: Blue moon (second full moon of a month)
All month: Morning planets: Mars in Leo and Saturn in Virgo