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Starwatch - July 2010

June 15, 2010


By Deane Morrison

This July brings us one of the loveliest full moons we’re ever likely to see. Rising in the Twin Cities at 8:32 p.m. on the 25th, it becomes full just five minutes later. The sun sets at 8:47 p.m., so from the proper vantage point you may see both a gorgeously round moon and a red sun sitting on opposite horizons.

This full moon was known to Algonquin Indians as the buck moon, for the new antlers pushing up from the heads of male deer. They also called it the thunder moon, since thunderstorms are now most common.

July might be called the month of the scorpion, for this is when the slithery form of Scorpius is highest in the evening sky. Marked by its heart—the gigantic red star Antares—Scorpius comes out low and almost due south, stretching its claws westward toward Libra.

East of Scorpius, the well-named Teapot of Sagittarius dips to pour its contents onto the scorpion’s tail. Above the handle of the Teapot hangs the little Teaspoon of stars. Together, these constellations shout “summer” to the experienced star watcher.

In the west, two bright stars and three planets begin the month strung in a rough line. Start by looking just to the west of Scorpius early in the month; you’ll see the bright star Spica, in Virgo. Moving westward, you’ll next see Saturn, then Mars, then bright star Regulus, in Leo, and finally Venus.

The night of the 9th, Regulus passes Venus and heads into the sunset. But the three planets remain, and they proceed to put on a show of togetherness. At the start of the month they span 38 degrees of sky, but that shrinks to just eight degrees by the 30th, when Saturn glides above Mars. And to add to our viewing pleasure, a waxing crescent moon makes the rounds of the planets between the 13th and 16th.

In the east, Jupiter rises earlier every evening, brightening all the while. It shines near the Circlet of Pisces, a somewhat dim but pretty star group below the Great Square of Pegasus.

On the 6th, Earth reaches aphelion, its farthest point from the sun. At that moment we’ll be 94.5 million miles away from our parent star. We don’t, of course, feel any less heat because of this because the variation in Earth’s distance from the sun is too small. The ancient Romans, however, noted the intense heat of July and put it down to Sirius, the brilliant Dog Star, rising at the same time as the sun and adding its heat. The name stuck, and even today the sweltering days of July and August are known as the Dog Days.

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

6/18/10 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.

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