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Starwatch February 2011

January 18, 2011


Sapas Mons volcano on Venus.

Venus's Sapas Mons (foreground) and Maat Mons volcanoes are among the rugged features of our hot, cloudy sister planet.

By Deane Morrison

A changing of the guard begins in February, with Jupiter dropping through the evening sky to the west just as Saturn stages an entrance to the east.

February opens with Jupiter's golden orb shining above the western horizon. But its dominance wanes with the winter, and by the end of March it is destined to become lost in the sun's afterglow.

In contrast, Saturn rises about 90 minutes before midnight at the beginning of February and appears earlier each night. With Jupiter already having set, Saturn is a solitary sojourner across the night sky, devoid of planetary company until the predawn hours. But its rings are open enough to make it well worth a look through a telescope.

Venus still rules the morning sky, but it is starting to sink into the sun's foreglow. Catch it in the first two weeks of the month, before it loses too much altitude and luster.

In February Sirius, the brightest of stars, and its constellation, Canis Major, are at their highest in the south after nightfall. If you've never seen Canis Major, grab a star map and try tracing the outline of Orion's bigger hunting dog.

If you’re looking for hard-to-find constellations, turn your sights just below Orion, where Lepus, the hare, crouches. Sharp eyes (or a pair of binoculars) will help you find its “rabbit ears” sticking up in a faint “V” just below Rigel, the southwestern star in Orion’s hourglass figure.

Besides being fun, Groundhog Day is a tradition with astronomical roots. Our modern rodent-run holiday started out as the Celtic feast of Imbolc, or lamb’s milk, celebrating the lambing season. It was one of four cross-quarter days falling halfway between a solstice and an equinox. As the reasoning went, a cloudy, shadow-free day was a harbinger of rains, a softening earth and an early start to spring planting. But a clear day meant more cold, frozen ground and shivering.

Some of us may equate February with the dead of winter, but late February always has a couple of treats in store. Look an hour or two after sunset for a soft, broad finger of light pointing back along the sun's path. This is the zodiacal light, a reflection of sunlight off a disc of dust that stretches far into space in the plane of the solar system. 

And if you’re really lucky, you may see a very faint oval of light against a dark sky, exactly opposite to wherever the sun is at the time. This is the Gegenschein, or counterglow, and it is also the result of reflections off dust. The best time to look is close to midnight, when the Gegenschein will be high in the south—the spot where a full moon would be at that time. In fact, the dust particles in the Gegenschein shimmer so much because we’re seeing them, too, in full phase. 

Algonquin Indians called February’s full moon the snow moon, as snows tend to be heaviest this month. It was also known as the hunger moon, because hunting was hard in the deep snow. This year it rises the evening of the 17th and reaches perfect fullness several hours later, at 2:36 a.m. on the 18th. 

The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see:

Duluth, Marshall W. Alworth Planetarium: www.d.umn.edu/planet

Twin Cities, Department of Astronomy (during fall and spring semesters): www.astro.umn.edu/outreach/pubnight

1/21/11 Contact: Deane Morrison, University Relations, (612) 624-2346, morri029@umn.edu

Find U of M astronomers and links to the world of astronomy at http://www.astro.umn.edu.
 

Tags: College of Science and Engineering

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