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The Sky This Week, 2011 January 11 - 18

The days are getting longer, and the weather on Jupiter and Saturn heats up!
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Jupiter, 2011 JAN 04, 00:29 UT
Imaged with the U.S. Naval Observatory's
30.5-cm (12-inch) f/15 Clark/Saegmüller refractor


The Moon waxes in the evening sky this week, climbing up to join the stars of the Great Winter Circle as she brightens each night. First Quarter occurs on the 12th at 6:31 am Eastern Standard Time. Luna straddles the knotted stars of the Pleiades cluster on the evenings of the 14th and 15th, then stands high above Orion’s upraised club on the 17th.

January 12th marks the end of the doldrums of winter. For the past week we have been experiencing the latest sunrises of the year here in Washington, but each day from now until the summer solstice the Sun will come up a little earlier each day. We experienced the earliest sunsets back in early December. By the end of this week Old Sol will be setting half an hour later than he did back then.

The stars of the Great Winter Circle may be found astride the meridian during the late night hours. This is when you’ll see the bright members of Orion confidently striding across the southern sky. The Hunter’s club reaches up above the ruddy star Betelgeuse, seemingly ready to smite the similarly reddish eye of Taurus, the Bull, high to Orion’s west. Springing up behind Orion’s heels are his two hunting dogs, the larger one marked by the dazzling blue star Sirius. This star is the brightest in the entire sky, its icy blue tint often distorted into all the colors of the rainbow by turbulence of passing winter storms. The star’s name means "the scorching one", and it has figured prominently in human timekeeping activities for well over 5000 years. The ancient Egyptians regulated their secular year by its rising just before the Sun. Once every 1500 years this "heliacal" rise of the star would correspond with the new year observed in their religious calendar. Their civilization lasted long enough for this event to be recorded three times! Today, Sirius once again marks the start of the New Year; in the Gregorian calendar it crosses the meridian at midnight local time.

Our New Year finds us preparing to bid farewell to a bright planet that’s been a fixture in the evening sky for several months now. Giant Jupiter is still very prominent in the southern sky as evening twilight fades, but his time in the dark of full night is beginning to come to a close. By the end of evening twilight he’s heeling over to the southwestern part of the sky, and now sets shortly after 10:00 pm. Jupiter has been putting on a grand show for small telescope owners this year as his atmosphere has been particularly busy. When he first came into view in the early morning sky last spring he was missing one of his most prominent dark cloud belts. This feature has now begun its much-anticipated return, and those of us who follow these things will watch it develop until Jupiter is lost in the twilight glare.

In the meantime the solar system’s second-largest planet, Saturn, is poised to take Jupiter’s place as the target of our telescopes. Not to be outdone by his bigger and brighter rival, Saturn has also developed a large atmospheric disturbance that’s visible in amateur telescopes. The ringed planet now sports an enormous white plume in his northern temperate zone and may be developing a second one closer to his northern pole. Weather on the outer planets is almost never boring!

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