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Last modified: Wednesday, August 1, 2007

STAR TRAK

Perseid meteors peak in a dark sky

FOR IMMEDIATE RELEASE
Aug. 1, 2007

BLOOMINGTON, Ind. -- The annual Perseid meteor shower is eagerly anticipated by skywatchers. This year's Perseids will peak in a moonless sky, creating ideal conditions for a meteor-watching party.

This shower is one of the most popular every year because it happens on warm summer nights, when gazing at the starry sky is a pleasure that only clouds can spoil. The Perseids will peak the evening of Aug. 12-13, the same date as the new moon. You can expect to see 60 to 90 bright meteors per hour in a clear sky, and some will have smoke trails that last several seconds after the meteor has vanished.

Avoid artificial lights as much 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. Try facing east if you have a clear view in that direction, and look about half-way up the sky from the horizon. You won't need binoculars or a telescope. The meteors move too fast for that, and you can see them best without optical aid.

The meteors may appear anywhere in the sky, but they will seem to originate from a point called the radiant in the constellation Perseus, which gives the Perseids their name. The higher the radiant 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, with the bright stars Capella and Aldebaran and the Pleiades star cluster below it.

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 longer.

The Perseid shower will be visible for most of August, though there will be fewer meteors to see the farther from the peak date you watch. If the peak on Aug. 12-13 is hidden by clouds, try looking for meteors again as soon as the night sky is clear.

Most meteor showers happen when Earth crosses the orbit of a comet. The meteors are caused by particles 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 "river of rubble," ranging in size from sand grains to pebbles, each particle slams into 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"). All of this happens about 50 miles above the ground, regardless of how close some meteors may appear.

More information about the Perseids and other meteor showers is available at http://www.space.com/spacewatch/070712_perseid_meteors.html.

Lunar eclipse

A total eclipse of the moon will be the major event of August for much of North and South America and East Asia. The eclipse will be centered on the Pacific, and observers will see the darkened moon sinking low in the west before or during dawn on Aug. 28. Those near the West Coast will see the entire event. For the eastern United States and Canada and much of South America, the show will be cut short by a combination of moonset and sunrise. For details see http://www.skyandtelescope.com/observing/objects/eclipses/Eclipses_in_2007.html.

Light pollution

If you are looking at the constellation Cassiopeia on a clear summer night, and you can't see the Milky Way sprawling high across the sky from the northern to the southern horizon, then your sky has significant light pollution -- and that's the case for about two-thirds of the world's population. See http://www.darksky.org/ for information on this dimming of the night sky caused by excessive artificial lighting, much of which is wasted.

Planets

Jupiter will continue to be a fine "evening star" in the southern sky, the first object to appear after sunset. Observers with telescopes should have several hours of good viewing each night before atmospheric disturbances start spoiling things as the planet sinks lower.

Mars will rise around 1 a.m. local time at the beginning of the month and an hour earlier by month's end. Though still small, the red-orange planet is gradually brightening. It will pass to the lower right of the Pleiades star cluster on Aug. 7, and on Aug. 22 it will cruise past the bright orange star Aldebaran in the constellation Taurus the Bull. The two objects are almost identical in color, but Mars will be twice as bright as Aldebaran. The combination of Mars, Aldebaran and the constellation Orion the Hunter rising in the southeast will be an eye-catching sight in early morning.

Venus, Saturn and Mercury will be out of sight during most of August, too close to the sun for viewing.

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. 5, new on Aug. 12, at first quarter on Aug. 20 and full on Aug. 28.