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The Night Sky of December

Dr. Wayne Wooten
Professor of Astronomy

For December, the full moon, the "Long Night Moon" occurs on December 3, 2017. The last quarter moon is on December 10th. The waning crescent moon passes just north of Mars on the morning of December 13th, and then north of Jupiter the following morning; this is also the peak for the best meteor shower of the year. The Geminids will begin coming out of the northeast shortly after sunset, and peak at about a meteor a minute about 3-4 a.m. on the 14th. The moon is new December 18th. First quarter moon is on December 26th.

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 2017; 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: http://hubblesite.org/explore_astronomy/tonights_sky/

Mercury and Saturn are briefly visible just after sunset during the first week of December, but lost in sunís glare for rest of month. Venus is also lost in the Sunís glare, to reappear in the dawn in early 2018. Mars and Jupiter

are in the dawn sky, with closer Mars overtaking more distant Jupiter throughout the month, with the two only 3 degrees apart on New Yearís morning.

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. Between the foot of Aquarius and Fomalhaut is the Helix Nebula, the closest planetary nebula. This fine shot of the "Eye of God" by EAAA members Chris and Gina Gomez probably anticipates what our own solar system will look like 6 billion years hence, when the evolved red giant sun passes through a similar cosmic strip tease stage.

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 Pegasusíí 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 Andromedaís 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 Perseusí 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 Betelgeuse 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 starbirth all over the place.

Last but certainly not least, in the east rise the hunterís 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 Yearís sky feast.

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