Friday, August 11, 2000

Shooting-star show peaks Saturday

By Anita Howard
Enquirer contributor

        On Saturday morning, the Perseids meteor showers will reach their peak. If we're lucky, the night sky will rain “shooting stars.” So grab a lawn chair, plan to get up early and enjoy the show.

        Meteor showers are exciting because they are intense and predictable. As many as 50 to 150 shooting stars may be seen per hour on a clear night by the unaided eye. This far exceeds the eight sporadic shooting stars per hour seen during a normal night.

        Showers are predictable because the Earth's revolution encroaches upon a nest of celestial debris at the same place in space at the same time each year.

        That means we know the Perseid shower will occur in August, the Leonid shower in November and the Andromedid or Bielid shower in December.

        We are able to predict where the celestial debris lies because it is the rubble left by a periodic or returning comet. The Perseids are remnants of the Comet Swift-Tuttle, which orbits the sun every 120 years. It was last here in 1992.

        “When comets move through the inner solar system they form a huge cloud of dust, gas and pieces of rocky debris,” explains Paul Nohr, astronomer at the Cincinnati Observatory Center. “Being small, comets have a weak gravitational field and easily lose some of their messy surroundings due to light pressure, solar wind and explosive outgassing from the comet's surface.

        “This produces the long tails of gas and dust we usually associate with comets. The dust grains and larger particles of ices and rock eventually fall away sprinkled along the path.

        “Think of this trail of comet leftovers as a river through space. If this river (meteor stream) intersects the orbit of the Earth we see "fireworks' each time one of the particles slams into our atmosphere,” Mr. Nohr says.

        “The Perseid stream is well-populated and fairly evenly distributed. It intersects our orbit at a point occupied by the Earth near the end of the second week of August. Like clockwork, we are closest to the center of the Perseid stream around Aug. 12, when the meteoroid impacts with the Earth reach a peak.”

        The Perseid shower was first recorded by the Chinese in 36 A.D. They were identified as shooting stars that occurred in August, not as a meteor shower.

        One of the most intriguing legends appeared in medieval times, as the tears of St. Lawrence. As superstition has it, tears of fire fell from the night sky on Aug. 10, the anniversary of his martyrdom. Saint Lawrence was tortured and killed on that date in the year 258 by the anti-Christian emperor Valerian.

        It was not until 1835 that Adolphe Quetelet of Brussels, Belgium, was given credit for discovering the meteor shower, but he could not identify the radiant or origin of the shower.

        John Lock, a Cincinnati physician and headmaster at a girls' school, was the first person to discover that the August meteor shower appeared to radiate from a small area in the Perseus constellation, thus the Perseid meteor shower.

        “The best time to go out to look for the Perseid meteors will be about 4:30 a.m. on the morning of Aug. 12,” Mr. Nohr says. “Find a nice open area and flop back in a lawn chair to observe as much of the sky as possible with a slight preference for the northeast. In the suburbs you may see 10 to 30 per hour; in the country, possibly 40 to 100.

        “Take the bug spray, you may want it,” he says. “Good luck.” Skywatching is a monthly column by Anita Howard, Observatory program director. For information, call (513) 321-5186.


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