Last modified: Monday, August 1, 2005
Perseid meteors dart across the summer sky
BLOOMINGTON, Ind. -- The annual Perseid meteor shower is one of the most popular because it happens on summer nights when the viewing is easy. The Perseids will peak on the nights of Aug. 11-12 and Aug. 12-13, and the first-quarter moon will obligingly set before midnight, making way for the celestial display.
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, since the number of meteors will rise during the pre-dawn hours.
The Perseid shower's peak rate is about one meteor per minute in a clear sky with no bright sources of light nearby. 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 makes it easier to watch the sky.
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 and the brilliant orange planet Mars to the right (south).
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.
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_1557_1.asp.
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, then your sky has significant light pollution -- and that's the case for about 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.
Venus will be a beautiful white "evening star" low in the western sky after sunset during all of August. Easily visible above the western horizon, it will reach its highest elevation on Aug. 17 and set more than an hour after the sun.
Jupiter will appear in the west-southwest after sunset to the upper left (south) of Venus. Jupiter is the second-brightest planet, yielding only to Venus, and these two brilliant objects will move steadily toward each other during the month. By Aug. 31, they will both fit behind your little finger held at arm's length, a special treat for anyone even casually glancing at the western sky. The two planets will be closest the next night. The much fainter star to their left (south) is Spica.
Earth is gradually catching up to Mars in our smaller, faster orbit. The red planet will appear a couple of minutes earlier each night in August, rising well before midnight by month's end and blazing bright red-orange high in the south before dawn. Mars will rapidly grow brighter and larger as the month passes.
Saturn will return to view in August after its journey behind the sun, becoming visible low in the east-northeast in morning twilight in the second half of the month.
Mercury will quickly climb out of the solar glare to join Saturn in the predawn sky, and they will be closest on Aug. 18 low in the east about an hour before sunrise. Binoculars will help you pick out fainter Mercury below yellow Saturn in the brightening sky. After that, the two planets will gradually move apart as Mercury becomes much brighter.
Viewing information and graphics for the planets are available at http://www.space.com/spacewatch/.
The moon will be new on Aug. 5, at first quarter on Aug. 13, full on Aug. 19 and at third quarter on Aug. 26.