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The Sky This Week, 2011 January 18 - 25

The "Old Moon" for the New Year, and exploring a stellar nursery.
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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 brightens the late night and early morning skies this week, with Full Moon occurring on the 19th at 4:21 pm Eastern Standard Time. The year’s first Full Moon is popularly known as the Moon After Yule or the Old Moon in traditional sky lore. Like the Full Moon in December it occurs at a high northerly declination and because of this often appears particularly bright. This effect is further enhanced if there’s snow on the ground, and in rural areas it is quite easy to find your way around all night long with the Moon so high in the sky. Look for Luna near Castor and Pollux, the Twin Stars of Gemini, as the week begins. On the evening of the 21st she lies about six degrees to the south of the bright star Regulus, heart of Leo, the Lion. Before dawn on the 25th she forms an attractive triangle with the golden-hued planet Saturn and the bright blue star Spica.

We are now at the time of the year when winter’s constellations are at their best in the evening hours. Even with a dazzling Moon nearby the bright stars of the Great Winter Circle will lead you on a tour of some of the night’s most impressive constellation figures. By the week’s end you can begin to make out the fainter members of these star groups as the Moon rises later. The easiest figure to discern is that of Orion, the Hunter, whose three bright blue "Belt Stars" mark the center of an asterism that’s visible from every inhabited part of the globe. Orion’s stars appear so bright because most of them formed in the same region of space and share many common characteristics. They are all relatively young stars that have intrinsic brightnesses that exceed that of the Sun by a factor of several thousand times. Tracing their apparent motion paths back through a few million years of time leads to a spot in the middle of a small gaggle of stars known as the "Sword". The center "star" of the sword is the home of the Great Orion Nebula, a vast cloud of hydrogen and helium that is still producing new stars to this day. Binoculars or a small telescope reveal the gaseous nature of this area, even under the light of the Moon. From a dark locale under good conditions a modest telescope will reveal swirls and eddies of this nebulous mass, one of the most spectacular sights our night sky has to offer.

Another spectacular sight that’s much closer to home is the bright glow of the planet Jupiter. Old Jove has dominated the sky for the past several months, but he is now only well-placed in the early evening. His bright cheery glow beams down from the western sky until the late evening, and he now sets at around 10:00 pm. You’ve still got a little time to catch a good glimpse of him in the small telescope, but you’d better act quickly. The Sun is in hot pursuit of the giant planet, and in a few more weeks he’ll be gone until next fall.

Golden Saturn can be glimpsed now just before local midnight. By week’s end the ringed planet rises just after 11:00 pm, and in several more weeks you’ll be able to catch a glimpse of him before turning in for the night. Right now the best time to view him is before sunrise, but he’s made it worth your while to do so with the eruption of a large storm in the cloud belts of his northern hemisphere. This feature should be fairly easy to see in six-inch or larger telescopes in the clear, calm air before dawn.

Dazzling Venus can be found in the southeastern sky in the morning twilight hours. This week finds her in the company of Antares, the ruddy star that marks the heart of Scorpius, the Scorpion. Venus starts the week some eight degrees north of the star. By the week’s end she will have drifted to a point some 12 degrees to the east.

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