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Starwatch August 2011

July 21, 2011

Betelgeuse up close.

The red supergiant star Betelgeuse, in Orion, is seen here in infrared light. It's enveloped in a nebula (a cloud of gas and dust) resembling flames, which forms as the gigantic star sheds mass into space. The tiny, nearly invisible red circle in the middle has a diameter about 4.5 times that of Earth's orbit and marks Betelgeuse's visible surface. The black disc corresponds to a very bright part of the image that was masked to allow the fainter nebula to be seen. Credit: ESO/P. Kervella

By Deane Morrison

The end of summer brings the laid-back water constellations into the evening sky and gives us our last good look at the stars of Scorpius and Sagittarius.

Those two constellations move from south to southwest during August. Scorpius, slithering across the southern horizon, leads Sagittarius and its starry Teapot toward their seasonal oblivion.

The Summer Triangle soars in the south. It comprises Deneb in Cygnus, the swan, and Vega in Lyra, the lyre, both very high; and Altair in Aquila, the eagle, the lowermost point of the triangle. Just east of the Triangle, see if you can find little Delphinus, the dolphin, as it leaps toward the Great Square of Pegasus, now coming into view in the east.

Below Altair is dim, chevron-shaped Capricornus, the sea goat. Moving eastward we find the spidery form of Aquarius, the water carrier, and, underneath the Great Square, the Circlet of Pisces, the fish. In the west, brilliant Arcturus pulls kite-shaped Bootes, the herdsman, down toward the horizon.

Saturn also falls in the west. By month's end the gorgeous planet sets only about 90 minutes after the sun. But another bright planet soon comes along. Jupiter, a beacon in the east, rises around midnight on the 1st but closer to 10 p.m. by the 31st. 

In the predawn sky, Mars appears ever higher in the east, gliding through Gemini en route to Cancer. On the 22nd and 23rd, the Red Planet forms the westernmost point of a thin isosceles triangle with Castor and Pollux, the brightest stars in Gemini. West of Mars you'll see Orion, Taurus and other bright winter constellations, plus Jupiter riding high in the southeast.

Moonless mornings in August and September are the times to look for the elusive zodiacal light. This broad, fingerlike glow points up from the eastern horizon along the sun's path between about one and two hours before sunrise. Called the "false dawn" in the "Rubaiyat" of Omar Khayyam, it is caused by sunlight reflecting off dust in the plane of the solar system.

August's biggest show—the Perseid meteors—will be a flop this year, thanks to a nearly full moon washing out all but the brightest meteors. The shower peaks the night of the 12th-13th.

That full moon shines the next night. Algonquin Indians called it the sturgeon moon, for the iconic Great Lakes fish that is most easily caught this time of year. As the moon wanes, though, it glides through the morning stars. Catch it on the 25th, when it appears close to Mars.

In astronomical news, the Hubble Space Telescope has just discovered a fourth planet orbiting Pluto. Temporarily named P4, it is only 8 to 21 miles in diameter, compared to 20 to 70 miles for Pluto's moons Nix and Hydra, 648 miles for Pluto's major moon, Charon, and 1,400 miles for Pluto itself. The sharp-eyed Hubble spotted tiny P4 from a distance of 3 billion miles. 

Astronomers think the entire Pluto system may have been created by a collision between Pluto and a planet-sized body when the solar system was young. The collision would have splattered material that coalesced into the moons, a scenario similar to the way scientists believe Earth's moon was formed.

If you're near the University of Minnesota's Twin Cities campus in August, check out the ExploraDome, a portable mini-planetarium operated by the Minnesota Planetarium Society. It will be at the Bell Museum of Natural History, 10 Church St. S.E., Minneapolis, for shows at 1, 2, and 3 p.m. August 2, 10, 17 and 23. Shows are free with museum admission. For more information, see

The Marshall W. Alworth Planetarium at the University of Minnesota, Duluth sponsors free public shows. For more information, see

Contact: Deane Morrison, University Relations, (612) 624-2346,

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