University of Minnesota
February 18, 2011
Jupiter is slipping from the evening sky. This composite image from NASA shows the planet's biggest storm system--the Great Red Spot--and the shadow of its moon Europa.
By Deane Morrison
Watching the stars is getting easier now that the bitter cold of January and February is yielding to the inevitability of spring. But as winter slips away, so do some of the brightest planets.
In the west, mighty Jupiter drops steadily toward the sun's afterglow. In mid-March, however, you may spot dimmer but speedier Mercury on its way up. Mercury passes Jupiter on the 15th and continues to soar until the 22nd. Then it, too, begins to plummet from the sky.
Meanwhile, Venus, now an ornament in the eastern predawn sky, takes a slower approach to losing altitude and will stick around for a few more months. Catch it on the 1st and the 31st, when old crescent moons appear very near the planet.
Saturn begins the month rising two hours after the sun sets and ends it rising nearly at sunset. Its glorious rings narrow a bit, but it's still the prettiest planet in sight. Look for it in the east in the evening and in the west in the wee hours of morning.
Algonquin tribes called the full moon of March the worm moon, for the casts of earthworms that now begin to appear on the softening earth. In more northerly areas, it was known as the crow moon, for the cawing of these ubiquitous birds, or the crust moon, because during this season snow acquires a crust from cycles of melting and refreezing. The full moon shines the night of the 19th, the same day the moon reaches perigee, the closest approach to Earth in its orbit.
The knot of bright winter constellations is being carried toward the western horizon, thanks to the Earth's motion around the sun. Entering the sky in the east is a sure sign of spring: Leo, the lion, with its brightest star, Regulus, and the signature Sickle of stars outlining its magnificent head.
This is an excellent time to find the Beehive star cluster. Look west of Regulus to the bright star Procyon, then above an imaginary line connecting the two stars. The Beehive will be above the midpoint; use binoculars to catch the full beauty of this celestial gem.
Also, look to the north to see the Big Dipper "spilling its water" down toward the Little Dipper. See if you can make out the whole constellation Ursa Major, the Great Bear, of which the Big Dipper is part. Check out the double star at the bend of the handle and use the two "pointer" stars at the far end of the bowl to find Polaris, the North Star.
Polaris shines with the light of 2,000 suns, but being 430 light-years away, it ranks only as a second-magnitude star. Even so, Polaris has long been the beacon by which sailors could tell true north, thanks to its position almost directly above the North Pole. But that won't be true forever, because the Earth's orientation in space—and, therefore, the direction in which the North Pole points—wobbles like a top once every 26,000 years.
During one wobble cycle, the North Pole traces out a circle; projected on the heavens, the circle connects the successive points—one being very near Polaris—at which the pole points. In 13,000 years the pole will have completed half a cycle and will point to the spot on the circle opposite Polaris.
In another 13,000 years, however, we will have come full circle, and Polaris will again be the North Star. This time, though, it won't be quite as northern as it is now. That's because Polaris isn't standing still; like all other stars, it changes position against the backdrop of space as it follows its orbit through our galaxy.
Spring arrives officially at 6:21 p.m. CDT on the 20th, when the sun crosses over the equator into the northern sky.
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
2/18/10 Contact: Deane Morrison, University Relations, (612) 624-2346, firstname.lastname@example.org
Find U of M astronomers and links to the world of astronomy at http://www.astro.umn.edu.