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Hal Kibbey
IU Media Relations
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Last modified: Monday, August 2, 2004

STAR TRAK

Meteor shower and cluster of bright stars and planets

Photo by: NASA

BLOOMINGTON, Ind. -- The Perseid meteor shower, a summer tradition for many people, will have a dark sky for a backdrop this year. At the shower's peak on the night of Aug. 11-12, the nearly new moon will be only a thin crescent, allowing the Perseids to perform at their finest.

The best time to watch for the bright streaks of meteors will be between midnight and the start of morning twilight, when the part of Earth where you are watching the sky will be facing into the oncoming stream of meteors. The best strategy may be to get up very early on Aug. 12 instead of staying up late the night before. The number of meteors will rise during the pre-dawn hours, and the chance of seeing fireballs will increase as well.

The Perseid shower's peak rate is typically about 60 meteors per hour when the sky is clear and there are no bright sources of light nearby. Try to get away from as many artificial lights as possible to minimize the effect of light pollution, which can obscure as many as half of the meteors. A reclining lawn chair will make it easier to watch the sky, but no special equipment is needed.

The meteors may appear anywhere in the sky, but they will seem to originate from a point called the radiant in the constellation Perseus, from which the Perseids get their name. The higher this point is above the northeastern horizon, the more meteors will be visible. Perseus is just north of the W-shaped constellation Cassiopeia in the Milky Way.

Meteors near the radiant have short trails because we see them nearly end on, while those far from the radiant are seen from the side and therefore look much longer.

Most meteor showers happen when Earth crosses the orbit of a comet. The meteors are caused by particles of dust that were released from the comet's nucleus and left behind in space as the comet got closer to the sun. The Perseids come from Comet Swift-Tuttle. As Earth plows through this stream of debris, each particle hits our atmosphere at a speed of more than 50 kilometers per second and burns up almost instantly from friction with air molecules. The resulting heat momentarily creates a streak of glowing air that we see as a meteor (sometimes called a "shooting star" or "falling star").

More information about the Perseid shower is available at http://skyandtelescope.com/observing/objects/meteors/article_1289_1.asp.

Light pollution

If you can't see the Milky Way sprawling high across the sky from the northern to the southern horizon on a clear summer night, your sky has significant light pollution -- and that is the case for perhaps two-thirds of the world's population. See http://science.nasa.gov/headlines/y2001/ast01nov_1.htm for information on this dimming of the night sky caused by excessive artificial lighting, much of which is wasted.

Planets

Venus will be a beautiful white "morning star" in the eastern sky before dawn during all of August. It will be easily visible above the eastern horizon by 4 a.m. local daylight time, reaching its highest elevation on Aug. 17.

Saturn will return to view in August after its journey behind the sun. At the start of the month, It will rise in the east-northeast about 90 minutes before sunrise, far to the lower left (north) of brilliant Venus. The two planets will move toward each other as the month passes until they almost meet on the morning of Aug. 31. They will rise together that day nearly four hours before the sun, with the bright stars Castor and Pollux of the constellation Gemini the Twins close by on the left, the even brighter stars Procyon and Sirius nearby on the lower right (south), and the glittering stars of the constellation Orion the Hunter to the upper right. This unusual combination of so many bright stars and planets will be a spectacle low in the east an hour before sunrise.

The evening sky in August has no such sights to offer. Jupiter will be the only bright object, visible low in the west after sunset. It will set almost two hours after the sun at the beginning of the month, but only 45 minutes after the sun by month's end.

Mars will be so faint and low in the west that it will be lost in the glow of sunset during August.

Mercury will be out of sight as it passes between Earth and the sun.

Viewing information and graphics for the planets are available at http://www.space.com/spacewatch/.

Moon phases

The moon will be at third quarter on Aug. 7, new on Aug. 16, at first quarter on Aug. 23 and full on Aug. 30.