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Starwatch - August 2010

July 21, 2010


August opens with Lammas, or the festival of loaves, an ancient Celtic celebration of the season’s first harvest. The August 1 holiday was one of four cross-quarter days falling midway between a solstice and an equinox.

The Celts divided the year into light and dark halves, with the switchovers happening on the dates we call Halloween and May Day. By this reckoning, Lammas marks the halfway point in the light half of the year, an occasion to rejoice in its bounty. Its opposite is Imbolc, or lamb’s milk, on February 2, which we now know as Groundhog Day.

This year August holds two aces up its sleeve: very favorable conditions for the Perseid meteor shower and a close gathering of planets in the west. Look for the Perseids after 10 p.m. the nights of the 11th, 12th and 13th; this year, no moon will be around to interfere. Perseids tend to be fast and bright, with many leaving persistent trails. They radiate from a point in the northern constellation Perseus, which rises about 90 minutes after sunset.

These meteors represent the paths of dust left behind by Comet Swift-Tuttle, most notably during its 1862 appearance. As Earth hurtles through the dust cloud, numerous specks burn up in Earth’s atmosphere, producing the fireballs we all love to watch.

All month long, Venus, the brightest of planets, puts on a show—with a little help from its friends. On the 9th, look to the west as the sky darkens to see Venus pass Saturn. Moving eastward, Venus catches up with Mars on the 19th; these two planets then close in on the bright star Spica in Virgo. The three objects will form the tightest grouping on the 30th and 31st.

In the east, Jupiter begins the month by rising as the western planets are setting, but it appears
earlier every night. Its large bright orb traces a low trajectory across the night sky, just below the Circlet of Pisces, which itself is below the Great Square of Pegasus. With no bright stars in this area of the sky, Jupiter’s presence lends a welcome touch of brilliance.

August’s full moon arrives on the 24th. Algonquin Indians called this the full sturgeon moon, for the large Great Lakes fish that is easily caught this time of year. It was also known as the green corn moon.

The late summer stars are matchless in their variety. In the west, the kite-shaped form of Bootes hangs over the horizon, anchored by the bright star Arcturus. East of Bootes, find Corona Borealis, the Northern Crown; Hercules; and the Summer Triangle of Vega, Deneb and Altair. Further east, the autumn constellations of Pegasus, Pisces, Aquarius and Capricornus are wheeling into view. And in the south, take advantage of the last good time to see Scorpius and its bright red heart, the supergiant star Antares, before they disappear into the sun’s afterglow.

The University of Minnesota offers public viewings of the night sky at its Morris, Duluth, and Twin Cities campuses. For more information and viewing schedules, see:
Morris, UMN 16-inch telescope schedule: cda.mrs.umn.edu/~kearnsk/Telescope/PubObs.htm

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

7/21/10 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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