With new month of December upon us, people in the Northern Hemisphere will be treated to the longest nights of the year as the Winter Solstice arrives on the 22nd of this month. However, when it comes to changes in days' lengths, December is pretty much a story of steady 15-ish hour nights, give or take a few minutes at most, for much of the United States.. So, with all of this night, what's there to see?
By nightfall in December the fall constellations are all very well-placed for early (emphasis, early!) evening viewing. First up, we will have one last chance to see the summer constellations, provided you have a good West horizon. Hurry, though, they'll quickly disappear (at least in the West) for good by month's end. Moving onto more mainstream celestial landmarks for this time of year, the Great Square of Pegasus is high overhead and the Big Dipper is scraping the Northern horizon. Starting at the Great Square, look at the double string of stars coming of third base as they constitute Andromeda. High in the Northeast is ‘W’-shaped Cassiopeia, house-like Cepheus, and a twisted ‘V’ of stars, the mythological hero Perseus. Below Perseus is the bright Capella, alpha Auriga, and below his feet, the cloudy patch that is the Pleiades. In the early evening, the South, save bright Fomalhaut, is a dark void populated by the dim constellations of Capricorn, Aquarius, Pisces, and Cetus. If you stay up a little later as in a couple of hours after dark (which is no longer a chore/something you later regret doing at this time of year), you'll see all the winter favorite like unmistakable Orion in the South, which also serves as a winter signpost to the stars. From Orion, follow a line from his belt down to blazing blue Sirius, alpha Canis Major. Following that line up will bring one to Aldebaran, alpha Taurus the bull. Imagining a line starting at bright blue Rigel (Orion's left foot) through red Betelgeuse (Orion's right shoulder) will bring you to Castor and Pollux, alpha and beta Gemini. Other winter favorites to look for include Canis Minor, Cancer, and even Leo if you wait into the night a little longer. Early birds? Well, getting up just before the Sun will bring a spring preview in the form of Virgo, Bootes, Corona, Hercules, Corvus, and even Vega just ahead of the rising Sun.
Though still not exactly a good month for planet viewing, December is a bit of an improvement over November. As was the case last month, Mars hangs low in the Southwest sky virtually all month, setting roughly 3 hours after the Sun. Additionally, Venus re-emerges in the dusk sky this month, climbing higher as the month continues. Like Venus, Mercury drops from morning visibility to evening, re-emerging from the Sun's glare as a dusk object at month's end. Moving into the night, Jupiter is visible for most of the night as it heads toward opposition. As for Saturn, the ringed wonder continues its reemergence from the Sun's glare in the morning. By month's end, Saturn rises just over 3 hours ahead of the Sun.
Fun Thing to DoWith the longest nights of the year upon us, this is the time when you can see the same star twice in one night, as is on the set in the evening and on the rise in the morning. Despite this being the first month of winter, the summer stars are still visible in the sky at dusk. The stars of the Summer Triangle make perfect targets because of their brightness. As for what to do, simply go out and observe the stars of the Triangle (Vega is best as it is the brightest and will be first to rise in the morning). That done, either go to bed or stay up and enjoy the night until just before sunrise. At that point, go out and look in the Northeast for your chosen star's return to the sky. How many people can say they saw the same star twice in one night that way?