"Unusually Good" Meteor Shower Expected Tonight
for National Geographic News
Updated August 11, 2004
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The annual Perseid meteor shower, which peaks tonight, is poised to maintain its reputation for putting on a stellar show.
"It is really easy to view the Perseids compared to other meteor showers. Just put on some mosquito repellant and go outside," said Bill Cooke, a meteor-shower expert with the Space Environment Group at NASA's Marshall Space Flight Center in Huntsville, Alabama.
A nearly moon-free night and a predicted dense concentration of comet debris are combining to make this year's Perseids even better than usual, several astronomers are reporting.
Streaks across the sky over Death Valley, California, in an artist's
painting. Wednesday night and early Thursday morning, the Perseid meteor showeris expected to give a spectacular display.
Meteor showers occur when Earth orbits through trails of dust shed by comets on their repeated trips through the solar system. The tiny bits of debris, no larger than a grain of sand, light up when they strike Earth's upper atmosphere. In the process, they create what are commonly referred to as shooting stars.
The Perseid meteor shower officially peaks at 7 a.m. ET on Thursday, August 12 and astronomers say the best time to catch an eyeful of shooting stars?about 50 to 60 per hour?is from midnight to dawn.
"It's a very reliable shower. You can bet your bottom dollar that people will see meteors," said Mark Bailey, director of the Armagh Observatory in Northern Ireland.
The Perseids are known as fast and bright meteors, as Earth encounters them almost head-on, Cooke said. They enter Earth's atmosphere at a velocity of about 37 miles (60 kilometers) a second.
Astronomers around the world are particularly excited about the predicted encounter at about 5 p.m. ET on August 11. That's when Earth will enter a relatively young, and thus dense, filament of dust that boiled off comet Swift-Tuttle in 1862. Swift-Tuttle is the parent comet of the Perseids.
The encounter may produce an outburst of mostly faint meteors visible over Europe and Asia. Some predictions place rates as high as 200 meteors per hour. Sunlight will obscure these meteors for viewers in North America, but many other Perseids should be visible in the region.
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.
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.