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Starwatch August 2012

July 3, 2012


Two galaxies.

These two galaxies are currently separated by a mere 68,000 light-years, leading many astronomers to suspect that a close encounter is in progress. Image: NASA/Caltech-JPL

August gives us two full moons and the Perseid meteor shower, plus a tight grouping of two planets and a star in the evening sky. What more could we ask?

Low in the west after sunset, Mars, Saturn and the star Spica, in Virgo, form a fluid group that starts the month with Saturn above Spica and Mars to the west. The Red Planet moves steadily eastward, gliding between Saturn and Spica on the 13th. On the 21st, the three objects form a nearly equilateral triangle, with a crescent moon just below. Look 45 minutes after sunset; binoculars will help you find the planets and Spica.

The Perseid meteor shower peaks the night of the 11th-12th. Perseids are fast, bright meteors that often leave trails. This should be a good year for the annual shower, since the first meteors come into view between around 10 to 11 p.m. but the moon won’t rise until well after 1 a.m.

If you’re up early, try looking for the zodiacal light, a broad finger of light pointing up from the eastern horizon along the sun’s path. Moonless mornings in August and September are the best times to see the elusive light an hour or two before sunrise. It’s just sunlight reflecting off dust in the plane of the solar system, but rarely is dust so lovely. It can be mistaken for the first sign of daybreak and is called the “false dawn” in the “Rubaiyat” of Omar Khayyam.

Also in the morning sky, Venus is well up in the east at dawn and glides through the stars of Gemini. Jupiter, high in the southeast at dawn, spends virtually the whole month between the horns of Taurus.

We get full moons on August 1st and 31st, but whether the second is a blue moon is a matter of definition. The “Maine Farmers’ Almanac” defined a blue moon as the third of four whenever four occur within a season. But a misreading of the almanac led to the notion that a blue moon was the second of two full moons that fall in a single month, and that definition seems to have taken hold in recent years.

By the first definition, August’s second full moon isn’t blue, because June’s fell before the summer solstice and September’s falls after the autumnal equinox, leaving just two in August and one for July. But then, why pass up the chance to celebrate any moon any time? 

The full moon of the 1st will be prettier. It rises as a nearly perfectly round orb at 8:05 p.m. (in the Twin Cities) and reaches complete fullness at 10:27 p.m. Algonquin Indians called August’s full moon the sturgeon moon, for the Great Lakes fish that is most easily caught this time of year. It was also known as the green corn moon.

In the west, brilliant Arcturus leads its kite-shaped constellation—Bootes, the herdsman—down toward the horizon. East of Bootes hangs Corona Borealis, the Northern Crown, and just to its east is another hanger: upside-down Hercules, whose torso is set off by an hourglass-shaped arrangement of stars.

In the south, the well-named Teapot of Sagittarius is poised to empty its contents onto the tail of Scorpius. Can you see Mars and Antares, the red heart of the scorpion, at the same time? Antares’ name means “rival of Mars,” and with Mars closer to the sun’s afterglow, Antares may win this round in the brightness competition.

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

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

Check out the astronomy programs at the University of Minnesota's Bell Museum ExploraDome: www.bellmuseum.umn.edu/ForGroups/ExploraDome/index.htm

7/20/12 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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