Sky Report -December 2010

Jupiter at  Dusk and Venus at Dawn at Their Best for  December

The two brightest planets seen in our skies are Venus, our nearest neighbor world and Jupiter, the largest planet. Venus has an orbit around the sun about 70% the size of our path around the sun. So Venus can be seen well either just as it begins to be bright in the morning or as the last traces of the sun’s glow have disappeared in the evening. Venus’ brilliance is due to her closeness both to the sun and the Earth as well as her highly reflective clouds. In late October, Venus nearly passed in front of  the Earth and then appeared in the dawn in late November. In early December, Venus will be at her most brilliant at 40 times as bright as the brightest night star. In December, you can see Venus well up to 7 a.m. when the dawn begins to lighten the landscape. In  December, Venus will slightly fade as its distance increases from 37 to 55 million miles. Our neighbor  world starts the month in Virgo and then moves into Libra on December 12th. Venus shines with a steady light, not twinkling as the stars.
    
The planet Jupiter is also brighter than any night star but about 1/7th as bright as Venus owing to its greater distance both from the sun and Earth. But Jupiter is over 11 times as wide as  the Earth and covered  with highly reflective clouds. As it gets dark around 6 p.m., Jupiter is about half way up in the South, shining underneath the circlet of Pisces. A pair of binoculars held steadily will allow you to glimpse a few of Jupiter’s large moons, seen as tiny points of light on either side of the planet. In December, Jupiter will be about 450 million miles away; the sunlight reflected from Jupiter’s cloud tops takes about 40 minutes to reach our eyes. In the last few hours of the evening Jupiter moves into the western sky before it sets about midnight.

There will be a lunar eclipse in the early morning hours of Tuesday, December 21st. Lunar eclipses occur when the full moon drifts through the Earth’s shadow. In the middle of a  lunar eclipse, the moon will look rather dark, as the only light reaching the moon during the lunar eclipse is bent around the edge of the Earth. There will be a slight fading of the lower left side of  the moon around 1 a.m. Around 2:32 a.m., the moon will begin to enter the Earth’s shadow. At 3:17 a.m., the moon will be deepest in the Earth’s shadow. At 3:54 a.m., the moon begins to pull out of the Earth’s shadow. At 5:02 a.m., the moon is free of the Earth’s deep shadow.

The planets Mercury and Mars may be seen briefly low in the southwestern dusk around 5:30 p.m. in the first week of December. You need a flat horizon in that direction to see either of the planets. Mercury is about 5 times as bright as Mars which appears below and to the right of Mercury; binoculars are needed to see Mars through the twilight. The planet Saturn is in the southeastern 6:30 a.m. dawn, above and to the right of brilliant Venus. Between Venus and Saturn is Spica, the brightest star of Virgo and conspicuously twinkling.

There are two striking star groups on December evenings. In the Southeast is Orion with his three star belt.
Above and to the left of the belt is the bright pinkish star Betelgeuse in Orion’s shoulder. Below and to the right of the belt is Orion’s brightest star, white-blue Rigel. Orion on December evenings resembles a tilted hour glass. The belt points upward and rightward to Aldebaran, the bright orange star marking the eye of Taurus. Farther past Aldebaran is the 7 Sisters (Pleiades) star cluster, resembling a tiny dipper of stars. 

In the western sky is the Summer Triangle with the bright white-blue star Vega at the lower right corner. Above and  to the left of Vega is the Triangle’s top star, Deneb.  Deneb and stars below it form the Northern Cross. Deneb marks the top of the Cross. Below Deneb are three stars in a row for the cross arm. Below the middle of the cross arms is the star Albireo, the foot star of the Northern Cross.

Featured at the Frostburg State Planetarium in December is “Christmas, Hanukkah and Kwanzaa” with free public presentations on December 5th, 12th and 19th at 4 p.m. and 7 p.m. Our 45 minute program also includes an informal tour of the current evening sky. The Planetarium is in Tawes 302, just off the front lobby. Tawes Hall is across  from the Compton Science Center and behind the Performing Arts Center. Call (301) 687-7799 and leave your name and mailing address to receive a planetarium bookmark (includes a FSU map showing the Planetarium and parking areas nearby).   

By Dr. Bob Doyle

To contact Dr. Doyle, his mailing address is Planetarium, Frostburg State University, Frostburg, MD 21532 or by email at rdoyle@frostburg.edu.