The best known meteor shower of the year, the Perseid shower, is predicted to reach its traditional peak about 8 a.m. EDT on Monday, Aug. 12. This display is sometimes called St. Laurence's Tears because of the martyrdom of St. Laurence on Aug. 10, 258. Although other meteor showers are sometimes more spectacular than the Perseids, this shower is the most dependable from year to year. An average of about fifty meteors per hour can be seen during its traditional peak from a clear, dark location.
The best time for observing meteors is after midnight. From midnight until dawn more than half the sky we see is facing in the direction toward which Earth is moving as it revolves around Sun. Consequently Earth is colliding head-on with most of the pebbles and small ice particles that are vaporized by the friction of our atmosphere as they dissipate their energy of motion and become " shooting stars." This year's peak of the Perseids takes place at 8 a.m. on Aug. 12 when Moon is nearly at new phase, so the early morning hours of Aug. 12 and 13 will be free of moonlight. Moonrise for Morgantown is 5:01 a.m. on Aug. 12 and 5:57 a.m. on Aug. 13, little more than a half hour before sunrise. If it is clear we shall only have light pollution interfering with our viewing, and this can be overcome with a short drive into the country.
The Perseids are also visible, at somewhat reduced rates, for about four days on either side of the peak, with the period before maximum slightly more favorable than after. With moonrises approximately an hour earlier for each day before Aug. 12, however, this earlier period will be less desirable.
Some significant enhancements of the rate of meteors -- brief bursts -- were observed from 1991 through 1994 as a consequence of Comet Swift-Tuttle's passage into the inner part of the solar system in 1992. Swift-Tuttle is thecomet responsible for the debris along its orbit that provides the ammunition for the Perseid shower. A second peak, occurring about a half day before the traditional peak and associated with the passage of Earth through the comet's orbital plane, was well observed from its discovery in 1988 through 1994. This secondary peak seems to be associated with a ribbon of material located relatively close to Comet Swift-Tuttle. Last years peak associated with this debris was observed, but seemed weaker than in earlier years. These conclusions are not too certain, though, because of the difficulty of observing in the bright moonlight during last year's peaks. This year Earth passes through the region of this ribbon about 8 p.m. eastern daylight time on Aug. 11, so European observer's are favored for this early peak.
Meteor showers are named for the region of the sky from which most of the meteors appear to radiate even though they can be seen anywhere in the sky. The Perseids, for example, all seem to diverge approximately from the northern part of the constellation of Perseus -- the umbrella shaped pattern of stars between Cassiopeia and the Pleiades. Some showers are named for a star; the Delta Aquarids at the end of July seem to radiate from a region of the sky near the star Delta Aquarii. Perspective effects cause the stream of parallel moving meteors to appear to diverge from a point in the sky, just as parallel railroad tracks seem to diverge from a point in the distance.
The Perseid shower was recorded by the Chinese as early as the year 36 A.D. It was not until 1866, however, that the Italian astronomer Schiaparelli realized that the orbits of the meteors in this shower seemed to coincide with the orbit of a comet first observed in 1862 by the American astronomers Lewis Swift and Horace Tuttle. This association of the Perseid shower with the comet officially called Swift-Tuttle 1862 III was the first identification of a meteor shower with the orbit of a comet.
