The Night Sky of December
Dr. Wayne Wooten
Professor of Astronomy
As December begins, we see a spectacular conjunction between the crescent moon, bright Venus just below it, and slightly fainter Jupiter below both on Thanksgiving evening right after sunset. By Friday, November 29th, the waxing crescent moon moves to just below Saturn. The first quarter moon is December 3rd. As Jupiter disappears into
bright twilight by mid-December, Venus is still moving away from the Sun and passes within 2 degrees south of Saturn on December 11th. The Full Moon, the Yule Moon, is also that Wednesday evening. The waning gibbous moon will interfere with the peak of the Geminid meteor shower on the morning of December 14th.
The last quarter moon is on December 18th. The Winter Solstice is at 10:19 PM on December 21st, marking the shortest day of the year. A late Christmas present to observers bordering the Indian and Pacific Ocean is an annular solar eclipse at new moon on December 26th. As the year ends, the waxing crescent moon again passes just below Venus on December 28th; Saturn
is now low on the horizon, and also lost in the sun’s glare by early January, when Venus will be the only planet in the evening sky in early 2020.
While the naked eye, dark adapted by several minutes away from any bright lights, is a wonderful instrument to stare up into deep space, far beyond our own Milky Way, binoculars are better for spotting specific deep sky objects. For a detailed map of northern hemisphere skies, about November 30th visit the www.skymaps.com
website and download the map for December 2019; it will have a more extensive calendar, and list of best objects for the naked eyes, binoculars, and scopes on the back of the map. Also notable is wonderful video exploring the sky, available from Hubble Space Telescope website at www.hubblesite.org. Sky & Telescope has highlights of the best events for each week at
www.skyandtelescope.com
The square of Pegasus dominates the western sky. South of it are the watery constellations of Pisces (the fish), Capricorn (Sea Goat), Aquarius (the Water Bearer), and Cetus (the Whale). Below Aquarius is Fomalhaut, the only first magnitude star of the southern fall sky. It is the mouth of Pisces Australius, the Southern Fish.
The constellation Cassiopeia makes a striking W in the NW. She contains many nice star clusters for binocular users in her outer arm of our Milky Way, extending to the NE now. Her daughter, Andromeda, starts with the NE corner star of Pegasus’’ Square, and goes NE with two more bright stars in a row. It is from the middle star, beta Andromeda, that we proceed
about a quarter the way to the top star in the W of Cassiopeia, and look for a faint blur with the naked eye. M-31, the Andromeda Galaxy, is the most distant object visible with the naked eye, lying about 2.5 million light years distant. Overhead is Andromeda’s hero, Perseus, rises. Perseus contains the famed eclipsing binary star Algol, where the Arabs imagined
the eye of the gorgon Medusa would lie. It fades to a third its normal brightness for six out of every 70 hours, as a larger but cooler orange giant covers about 80% of the smaller but hotter and thus brighter companion as seen from Earth.
Look at Perseus’ feet for the famed Pleiades cluster; they lie about 400 light years distant, and over 250 stars are members of this fine group. East of the seven sisters is the V of stars marking the face of Taurus the Bull, with bright orange Aldebaran as his eye. The V of stars is the Hyades cluster, older than the blue Pleiades, but about half their distance.
Their appearance in November in classical times was associated with the stormy season, when frail sailing ships stayed in port. Aldeberan is not a member of the Hyades, but about twice as close as the Hyades; distances in astronomy can be deceiving.
Yellow Capella, a giant star the same temperature and color as our much smaller Sun, dominates the overhead sky. It is part of the pentagon on stars making up Auriga, the Charioteer (think Ben Hur). Several nice binocular Messier open clusters are found in the winter milky way here. East of Auriga, the twins, Castor and Pollux highlight the Gemini. UWF alumni can
associate the pair with Jason and the Golden Fleece legend, for they were the first two Argonauts to sign up on his crew of adventurers.
South of Gemini, Orion is the most familiar winter constellation, dominating the eastern sky at dusk. The reddish supergiant Betelguese marks his eastern shoulder, while blue-white supergiant Rigel stands opposite on his west knee. Just south of the belt, hanging like a sword downward, is M-42, the Great Nebula of Orion, an outstanding binocular and telescopic
stellar nursery. It is part of a huge spiral arm gas cloud, with active star birth all over the place.
Last but certainly not least, in the east rise the hunter’s two faithful companions, Canis major and minor. Procyon is the bright star in the little dog, and rises minutes before Sirius, the brightest star in the sky. Sirius dominates the SE sky by 7 p.m. and as it rises, the turbulent winter air causes it to sparkle with shafts of spectral fire. Beautiful as the
twinkling appears to the naked eye, for astronomers this means the image is blurry; only in space can we truly see “clearly now”. At 8 light years distance, Sirius is the closest star we can easily see with the naked eye. Below Sirius in binoculars is another fine open cluster, M-41, a fitting dessert for New Year’s sky feast.
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