The Sky This Month – December 2009
Posted by Brian Ventrudo
Despite the colder weather, the constellation Orion is always a welcome sight this time of year. The great mythical hunter bounds over the eastern horizon shield-first not long after sunset, facing Taurus, the angry V-shaped celestial bull with its glowing red eye, the star Aldebaran. Because of its location in the plane of the Milky Way, this constellation is full of enough fascinating sights for an entire winter of stargazing. To quote from our own Binocular Tour of the Night Sky:
“To the naked eye, to binoculars, and to the telescope, Orion is a gold mine of wonders. This great constellation embraces almost every variety of interesting phenomena that the heavens contain. Here we have the grandest of the nebulae, some of the largest and most beautifully colored stars, starstreams, star-clusters, nebulous stars, variable stars.”
If the first seasonal appearance of mighty Orion fails to stir your imagination, it may be time to turn in your telescope. But not this year, I hope.
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We’ll turn to Orion and its “gold mine of wonders” in more detail in the coming weeks. But the good stuff for viewing this month in the deep sky lies west of Orion. Cassiopeia is still well-placed overheard, as is the constellation Andromeda with the magnificent M31, the closest major galaxy to Earth. And M33 in Triangulum, the second-closest galaxy, lies nearby. M33′s low surface brightness means it reveals itself only in dark sky. And the Hyades star cluster, the V-shaped group of stars that makes up the head of Taurus, are always worth careful inspection in binoculars.
If you only have time for a quick peak in the night sky after dinner, try the double stars gamma Andromeda (Almaak), gamma Arietis (Mesarthim) and, the gold-reddish pair of eta Cassiopeiae. Very nice sights for a brief observing session with a telescope. If you have a little more time, peruse the open star clusters in this region, including the double cluster and M34 in Perseus, and M52 and M103 in Cassiopeia (see the image below). These sights are accessible with a small scope or binoculars, in rural areas and in cities.
The rich region of Cassiopeia and Andromeda, with the double stars Almaak (left), η (eta) Cass (lower right, near Shedir), and the star clusters M34 (upper left), the Double Cluster (upper middle), and M52 (lower right). Click to enlarge.
In the southern hemisphere, where the pleasant weather of late spring is upon you, Orion springs a handstand over the eastern horizon, and the star-poor galaxy fields of Fornax and Scupltor lie high in the sky. Try to spot the Silver Coin galaxy in Sculptor. It’s between Fomalhaut and Diphda, the bottom star in the belly of Cetus [see map]. Also known as NGC 253, this galaxy is hard to see from the northern hemisphere. But it’s right overhead this month after sunset for latitudes around 30-35 degrees south. The Silver Coin is the largest galaxy in the nearby Sculptor Group, which is just beyond our own Local Group.
The Sculptor Galaxy, NGC 253, between lower Cetus and the star Fomalhaut… click to enlarge.
An unusual event this month… two full moons. Because of an error in Sky and Telescope in 1946, this second full moon of a calendar month is now called a “Blue Moon”. The next occurs in August 2012.
• Full Moon: December 2, 7:30 Universal Time (UT… same as Greenwich Mean Time)
• Last Quarter: December 9, 00:13 UT
• New Moon: December 16, 12:02 UT
• First Quarter: December 25, 17:36 UT
• Full Moon (Blue Moon): December 31, 19:13 UT
Mercury. Well placed for northern observers this month, especially after mid-month. Look for this tiny planet about 5-6 degrees above the southwestern horizon just after sunset.
Venus. The beautiful planet is lost in the sunrise this month.
Mars gives the best show of all planets this month. In starts December in Leo, rising 5 hours after sunset. Then it moves into Cancer by months end, when it rises just 3 hours after sunset. You can’t miss it… it shines red, bright, and steady in the eastern sky after midnight, and high in the northern sky before dawn. And it’s getting closer to Earth, doubling in brightness by month’s end, making its closest approach at the end of January. This time, the planet will show a disk only half the size of the great opposition of August 2003. But a good telescope in steady sky will reveal some surface features, especially the white polar cap of the northern hemisphere.
Jupiter. Hovering in the southern sky, the king of planets still shines at an impressive -2.2 magnitude. Have a look early in the evening when the planet is at its highest. Jupiter is just 0.6 degrees from Neptune on December 20 and 21st.
Saturn. An ideal target for very early risers or insomniacs, Saturn rises around 1:30 a.m. local time in early December. It shines at magnitude 1.0 in western Virgo not far from Spica. The ring are still at just 4-5 degrees from edge on, but they present a lovely view in a telescope just before sunrise this month.
Uranus is lingering near the Circlet of Pisces this month.
• Another major meteor shower this month… the Geminids. The peak occurs on the night of December 13-14. You will see meteors on the night before and after. The Geminids can be as rich as the Perseids for those willing to venture into the December chill and lucky enough to get a clear night. North American and European observers should get the best view this year.
• In eastern and southern North America, the waxing gibbous moon covers part of the Pleiades from 7-10 p.m. EST.
• There’s a “Blue Moon” this month on December 31 (see above).
• December 21 is the shortest (longest) day of the year in the northern (southern) hemisphere. The solstice occurs at 17:47 Universal Time.
All of us at One-Minute Astronomer wish you a Merry Christmas and a happy holiday. Thanks very much for subscribing to our humble astronomy newsletter. We hope to keep writing our little articles into the new year, as time and fate permits.