The prediction of the crossing of the filament is based on scientific techniques gleaned from forecasts of the annual Leonid meteor shower in November, which changed scientific understanding of meteor streams.
For years astronomers believed that the debris following a comet formed a uniform trail along the elliptical path of the comet's orbit, Bailey said. The experts then realized that about every 33 years, coinciding roughly with the orbital period of Temple-Tuttle, the parent comet of the Leonids, a meteor storm would occur.
"It wasn't precisely every 33 years. Some were a few years before or a few years after, and it was very much hit-or-miss whether people were able to predict it," Bailey said.
Astronomers have now learned that when a comet ejects debris, it takes on a fine, filamentary structure. Over thousands of years this filament disperses, but when Earth encounters a fresh filament, an outburst of meteors occurs.
In recent years astronomers accurately predicted encounters with dense streams of dust from comet Temple-Tuttle, which treated observers to spectacular displays of Leonid shooting stars.
Comet Swift-Tuttle has a 128-year orbital period around the sun. The filament Earth is predicted to encounter on Thursday is called a "one rev" filament, since it boiled off just one revolution ago—in 1862—and this year is Earth's first predicted encounter with it.
"We're applying what we've learned from the Leonids to the Perseids. It will be interesting to see if things pan out," Cooke said.
Perseids
Swift-Tuttle was independently discovered by U.S. astronomers Lewis Swift and Horace Tuttle in 1862, but the earliest references to the Perseid meteor shower date back to A.D. 36 in Chinese records, according to information compiled by Gary Kronk, a St. Louis, Missouri-based science writer who maintains the Comets & Meteor Showers Web site.
References to the shower also appear in Chinese, Japanese, and Korean records throughout the 8th, 9th, 10th, and 11th centuries but only sporadically between the 12th and 19th centuries.
In European countries the Perseid meteors are also known as the Tears of St. Lawrence, because they occur days after a festival marking the Catholic saint's August 10 death in A.D. 258.
The Perseids were first recognized as an annual shower appearing to come from the constellation Perseus in 1835. Today they are the most well known of the annual meteor showers, consistently putting on a good show in the dog days of summer, when the weather is usually conducive to late-night stargazing.
"Only the Geminids beat them in terms of putting on a show year after year. Caught up with that, the Perseids are a summer shower, unlike the Geminids, which occur in December," Cooke said. "You don't have to bundle up with 6 inches (15 centimeters) of clothing to go observe them," he added.
For more meteor news, scroll down.
|
SOURCES AND RELATED WEB SITES
|
