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Hal Kibbey
IU Office of Media Relations

Last modified: Tuesday, August 1, 2006


Perseid meteors dart across the summer sky

Photo by: NASA

Aug. 1, 2006

BLOOMINGTON, Ind. -- The annual Perseid meteor shower will peak on a Saturday evening this year, creating ideal conditions for a meteor-watching party except for one uninvited guest -- the nearly full moon.

The Perseid shower is one of the most popular every year because it happens on warm summer nights, when gazing at the starry sky is a comfortable pleasure. The Perseids will peak early in the evening on Aug. 12. Unfortunately, the moon will be only three days past full, so moonlight will overwhelm the fainter meteors. Still, you can expect to see 20 to 30 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. Start the evening facing east and look about half-way up the sky from the horizon. When the moon rises in the east about two hours after sunset, turn your chair so you're facing away from the moon and look overhead. As the moon moves into the western sky, turn your chair back to the east to minimize the obscuring effects of the bright moonlight. In general, try to keep the moon out of your field of view.

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 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 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 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 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.

Information about other meteor showers happening during August is available at

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 for information on this dimming of the night sky caused by excessive artificial lighting, much of which is wasted.

Many photos of the Milky Way are available on the Internet, including this NASA movie showing eight Perseid meteors from last year's shower with the Milky Way in the background:


Jupiter will continue to be a fine "evening star" in the west-southwest after sunset, setting around midnight local time at the start of the month and two hours earlier by month's end. Observers with telescopes should have about two hours of good viewing time each night before atmospheric disturbances start spoiling things as the planet sinks lower.

Mars is about to pass behind the sun as viewed from Earth, and in August it will disappear into the glow of evening twilight in the west.

Venus will more than match Jupiter as a beautiful white "morning star" low in the eastern sky before sunrise during all of August.

Mercury will quickly climb out of the solar glare to join Venus in the predawn sky, and they will be closest on Aug. 10, low in the east less than an hour before sunrise. After that, the two planets will gradually move apart. Mercury will drop back into the glow of morning twilight during the last week of the month.

In the third week of August, while Mercury and Venus are still close, Saturn will return to view after its journey behind the sun, becoming visible low in the east-northeast before sunrise. Binoculars may be needed to find Saturn, since it will be considerably fainter than Mercury. Saturn will quickly rise to meet Venus and Mercury, and on the morning of Aug. 22, all three planets will be tightly bunched in a line with Mercury the lowest and Venus the highest. A very thin crescent moon will join the group to Saturn's upper left (north).

After Mercury has drifted away toward the horizon, Saturn will climb higher to meet Venus on the morning of Aug. 26. Faint yellow Saturn and brilliant white Venus will appear less than a half-degree apart near the eastern horizon. A clear view of the horizon will be needed to see all three of these pre-dawn planets.

Viewing information and graphics for the planets are available at

Moon phases

The moon will be at first quarter on Aug. 2, full on Aug. 9, at third quarter on Aug. 15, new on Aug. 23 and at first quarter again on Aug. 31.