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The Sky This Week, 2011 December 13 - 20

Moon-washed meteors and planets galore.
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 Jupiter & Europa, 2011 DEC 12


The Moon wanes in the morning sky this week, reaching the Last Quarter phase on the 17th at 7:48 pm Eastern Standard Time. Luna’s glare will unfortunately interfere with one of the year’s most reliable meteor showers, the Geminids, which will peak on the morning of the 14th. However, if you find yourself outside after about 10:00 pm on the evening of the 13th it’s still worth pausing for a few minutes to look for members of this display. Geminids are generally slower than meteors from the year’s other major showers and tend to be fairly bright. If you look in a direction away from the rising Moon you might see up to 20 meteors in an hour’s time. Luna starts the week off among the scattered dim stars of the constellation Cancer, the Crab. On the morning of the 16th she lies six degrees south of the bright star Regulus in Leo, the Lion. On the following morning look for the Moon some eight degrees south of Mars.

With the passing of our earliest sunset last week, this week finds Old Sol beginning to creep toward a later time of dipping below the western horizon. By the end of the week sunset will occur at 4:49 pm EST here in Washington, about three minutes later than it was on the 7th. Yet the nights are still getting longer due to the timing of the latest sunrise, which won’t occur until January 4th. Our longest night will occur on the solstice, which will fall on the 22nd. This month long "season" of solstice phenomena occurs because of a combination of our definition of standard time and the elliptical nature of the Earth’s orbit around the Sun. A more in-depth explanation may be found here.

These long winter nights are watched over by the familiar outline of the constellation Orion, who leads a bevy of bright stars across the meridian as the midnight hour passes. Orion’s distinctive "belt stars" straddle the celestial equator, which makes this bright star pattern visible from every inhabited part of the globe. Orion therefore figures prominently in the skylore of many cultures, portraying a person of kingly or god-like characteristics for over 5000 years. The two brightest stars in Orion have a striking color contrast that you won’t find in any other part of the sky. The bright blue star Rigel matches most of the rest of the Hunter’s stars in hue, but the star marking his shoulder, Betelgeuse, has a distinct reddish hue. Betelgeuse gradually changes brightness over long periods of time, with several complex superposed cycles involved. To my eyes this year it is close to Rigel in brightness. What do you think?

Venus is now beginning her rapid ascent into the evening sky. She is easy to spot in the southwest almost immediately after sunset, and as twilight gathers her glow becomes more prominent. Get used to her dazzle as the "evening star" for the next six months. She will have one of her best apparitions in years this spring, followed by an extremely rare transit across the Sun’s disc early next June.

Jupiter also becomes visible just after sunset. Old Jove is high in the eastern sky as twilight gathers, and he crosses the meridian at around 8:30 pm EST. This puts Old Jove in prime observing position during "prime time" hours. He is always a treat for the telescopic observer. After the Moon, Jupiter has the next-largest apparent diameter of any solar system object in the current night sky, and modest telescopes can show a wealth of detail.

Mars continues to rise a bit earlier each night, and by the end of the week he should be easily visible in the east by midnight. He’s still best viewed in the early morning hours among the stars of the constellation Leo. The red planet is becoming a bit brighter each night as Earth begins to close the gap on him in preparation for his opposition in March.

Saturn is now easily seen in the east at the onset of morning twilight. The ringed planet lies just over five degrees northeast of the bright star Spice. Star and planet offer an interesting color contrast for early risers to admire.

The fleet and fickle Mercury enters the morning sky for one of his rare appearances this week. Mercury may be found above the southeast horizon about half an hour before sunrise, and he will gradually brighten as he hangs here for the next couple of weeks.

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