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Starwatch July 2011

June 21, 2011


Saturn seen from above.

In this picture of Saturn from March 6, 2007, the planet's shadow on the rings highlights its 3-D appearance.

Photo: Cassini Imaging Team, SSI, JPL, ESA, NASA

By Deane Morrison

All planets are wanderers in the night sky—in fact, the very word "planet" comes from the Greek for "wanderer"--and in July the wanderer of the month is Mars. A "morning star" best seen about two hours before sunrise, the Red Planet glides through the stars of Taurus above the east-northeastern horizon.

As the month opens, Mars appears just above the V-shaped Hyades star cluster and Aldebaran (the eye of the bull) and below the Pleiades cluster. On the mornings of the 25th and 26th, Mars, having moved steadily eastward among its starry companions, sails between the points of the bull's horns.

If you can get up two hours before daybreak just once in July, do it on the 27th, when a waning crescent moon shines very close to Mars.

Saturn still rules the evening sky this month. A beacon in the southwest, it gleams to the upper right of the bright star Spica in Virgo. This is a good time to see its rings through a telescope because from our perspective Saturn is close to 90 degrees from the sun, an especially good position for the rings and globe to cast shadows that enhance its 3-D appearance.

Jupiter rises just before 2 a.m. on the 1st, but by the end of the month it starts appearing before midnight. Its bright yellowish globe will be well up in the southeast at dawn.

During the prime viewing hours of late evening, you'll see kite-shaped Bootes, the herdsman, high in the west. East of Bootes come, in order, Corona Borealis, the Northern Crown; upside-down Hercules; the brilliant star Vega, in Lyra, the lyre; and lovely Deneb in Cygnus, the swan. South of Vega and Deneb shines Altair, the brightest star in Aquila, the eagle. Together, these three stars are known as the Summer Triangle.

The full buck moon lights up the night of the 14th-15th. Its name comes from the velvety new antlers now sprouting on male deer. Algonquin Indians also called it the full thunder moon, in recognition of July's frequent thunderstorms.

Earth reaches aphelion, its farthest point from the sun, at 9:55 a.m. on the 4th. At that moment we'll be 94.5 million miles from our parent star.

While we're celebrating our national holiday, we can contemplate the fact that our planet follows an elliptical orbit, moving faster as we swoop closer to the sun and slowing down as our gravitational leash gets stretched. Earth's slower speed near the time of aphelion means that we spend more days of the year in this part of our orbit, where the sun is north of the equator. To see how this is true, count the days from the March to the September equinox; you'll see there are more days than if you count from the September to the March equinox.

If you'd like a first-person introduction to the night sky, check out the University of Minnesota Department of Astronomy's summer Universe in the Park program. Each event features a short public talk and slide show by a University astronomer and, if weather permits, viewing the night sky through multiple 8-inch telescopes. The program runs June 24—August 27 this year in Minnesota state parks. For more information and a schedule, visit http://www.astro.umn.edu/outreach/uitp/ or contact Karl Isensee at isensee@astro.umn.edu or (612) 626-1841.

The Marshall W. Alworth Planetarium at the University of Minnesota, Duluth sponsors free public shows. For more information, see www.d.umn.edu/planet

Contact: Deane Morrison, University Relations, (612) 624-2346, morri029@umn.edu

Find U of M astronomers and links to the world of astronomy at www.astro.umn.edu

Tags: College of Science and Engineering

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