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The Night Sky of December

Dr. Wayne Wooten
Professor of Astronomy

(2010) For December 2010, the Moon will be new on December 5th; the waning crescent moon passes six degrees south of Venus in the dawn sky on December 2nd.. The first quarter moon passes six degrees north of Jupiter overhead on December 14th; Jupiter is currently the only bright planet visible in the evening sky, although Mercury is briefly out in the SW twilight during the first week of December. The Geminid Meteor shower peaks on the morning of December 14th, so the first quarter moon will set near midnight and thus interfere little with the approximately a meteor a minute fall of cometary debris from the NE in predawn hours.

The winter solstice occurs at 5:42 PM CST on December 21, 2010; this is the shortest day of the year, and also time for a very early morning total lunar eclipse. For CST viewing, the umbral or dark portion of the earth’s shadow touches the Moon’s disk at 12:50 AM, with the moon totally eclipsed and probably blood red in appearance by 1:55 AM. The Moon starts to leave the umbral shadow at 3:10 AM, and is completely out by 4:15 AM. Bundle up and join us outside the Pensacola State College Planetarium for a public gaze…bring along your cell phone and digital cameras for great photos of this colorful and rare event. The photo of the month is by Gary Wiseman; it records the last such eclipse seen here, on February 20, 2008. It was taken near the end of totality, about 9:40 PM. The last quarter moon is on December 28th, with the moon passing seven degrees south of Saturn in the morning sky.

Mercury is visible in the first week of December low in the SW twilight, then passes between us and the Sun, and is visible in morning sky during the last week of the month. Venus dominates the morning sky, with the moon passing six degrees south of it on both December 2nd and again on December 31st. While Jupiter is the brightest object in the SW evening skies, it too will be swallowed up by the Sun in about three months. Saturn rises in Virgo about midnight, but if you use a scope to look for the rings, you find them brighter and more open than last year, when they were almost edge on.

The square of Pegasus dominates the western sky. 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. To the northeast, Andromeda’s hero, Perseus, rises. Between him and Cassiopeia is the fine Double Cluster, faintly visible with the naked eye and two fine binocular objects in the same field. 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. Check it out on a clear December evening, and see it the gorgon is winking at you. If so, then instead of being as bright as Polaris, Algol fade to be only as bright as kappa Persei, the star just to its south. Look at Perseus’ feet for the famed Pleiades cluster to rise, a sure sign of bright winter stars to come; 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 Pleaides, but about half their distance.

Yellow Capella, a giant star the same temperature and color as our much smaller Sun, dominates the NE 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 (closer to Capella, rising first about 7:30 PM as December begins) 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 by 8 PM. The reddish supergiant Betelguese marks his eastern shoulder, while blue-white supergiant Rigel stands opposite on his west knee. The three stars in a row that mark his belt have a Christmas association in Latin America. As "Los Tres Reyes", they stand for the three kings, bringing gifts to the Christ Child. 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. In amateur telescopes, I rank it next of Saturn as the most beautiful thing in the sky. The bright diamond of four very hot, young stars that light it up are the trapezium cluster, visible even in 60mm refractors.

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