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Hal Kibbey

Last modified: Monday, August 3, 2009


Perseid meteors celebrate summer

Aug. 3, 2009

BLOOMINGTON, Ind. -- Summer's silent fireworks will light up the sky when the annual Perseid meteor shower peaks before dawn on Aug. 12 and 13. This year, the Perseids will compete with the third-quarter moon, but there will still be many bright streaks in the sky.

This shower is one of the most popular every year because it happens on warm summer nights, when gazing at the starry sky seems like a natural thing to do. If moonlight does not interfere, you can expect to see 60 to 90 bright meteors per hour, some with smoke trails that last several seconds after the meteor has vanished.

The Perseids 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.

Avoid artificial lights as much as possible to minimize the effect of local light pollution, which can obscure as many as half of the meteors. 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 much too fast for that. The chances of seeing a fireball will be greatest near dawn, when Earth will be moving head-on into the meteor stream.

The Perseids 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 meteors 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 will have short trails because we see them nearly end on, while those far from the radiant will look longer because they are seen from the side.

A computer simulation of meteors streaking from the Perseid shower's radiant can be seen at: Scroll down to the fourth display.

Most meteor showers happen when Earth crosses the orbit of a comet, and the Perseids come from Comet Swift-Tuttle. The meteors are caused by particles released from the comet's nucleus and left behind in space. As Earth plows through this stream of debris, 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:


Jupiter will be at opposition on Aug. 14, appearing opposite the sun in our sky. Each evening in August, Jupiter will appear in the southeast as the sky darkens and dominate the southern sky all night. Observers with telescopes will have several hours of good viewing before atmospheric disturbances start interfering as the planet sinks lower in the southwest.

Venus will be a beautiful "morning star" in the east, rising three hours before the sun and easily outshining everything except the moon. Nearby on the left will be the bright stars Castor and Pollux of the constellation Gemini the Twins. Telescopes will show the asteroid Vesta a half-degree north of Venus on Aug. 25.

Mars will rise after midnight and be highest in the east as the dawn sky brightens.

Saturn will be sinking in the west during August, flickering into view 45 minutes after sunset at the beginning of the month and probably too low to spot without binoculars by month's end. Saturn's rings will disappear by Aug. 10, when they will tilt edge-on to the sun and no longer reflect light toward Earth.

Mercury will be very low in the west in bright twilight a half hour after sunset. Binoculars may help pick out the small planet near the horizon. Mercury and Saturn will gradually converge until they pass on Aug. 16.

Viewing information and graphics for the planets are available at

Moon phases

The moon will be full on Aug. 5, at third quarter on Aug. 13, new on Aug. 20 and at first quarter on Aug. 27.