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Aftermath of a meteor shower.

It wasn't the storm that many had hoped for, but it proved to be a spectacular shower. That's the consensus of observers who viewed the heavenly light show staged by the Perseid meteors on the night of Aug. 11.

Researchers had predicted that Earth's annual passage through the dusty debris making up the Perseids might this year provide an unusually intense meteor shower or even a storm (SN: 8/7/93, p.85). They based their forecast on the proximity of the Perseids' parent body, Comet Swift-Tuttle, which last December made its closest approach to Earth in 130 years.

Although Earth crossed the comet's orbital plane at about 9:15 p.m. EDT on Aug. 11, the number of meteors seemed to peak about two hours later-a puzzling feature also noted in the 1991 Perseid shower, says Brian G. Marsden of the Smithsonian Astrophysical Observatory in Cambridge, Mass.

Because different observers see different numbers of meteors depending on local viewing position and sky conditions, astronomers compare counts by using a standard called the zenithal hourly rate (ZHR). They define this rate as the number of meteors per hour that an average observer would see if the shower appeared to originate from directly overhead and sky conditions were such that the faintest stars visible had a magnitude of 6.5. Peter Brown at the University of Western Ontario estimates this year's peak rate at 350 ZHR, about three times higher than that of the average shower. A Perseid display intense enough to be considered a storm might have a rate 1,000 times higher than that recorded, Brown says.

Marsden adds that astronomers at Wise Observatory in Tel Aviv, Israel, reported an unusually high rate of nearly one meteor every five seconds lasting for about a half hour. But Brown says that all other observers reported rates at least 10 percent lower. Skies over southern France, Malta, and parts of Germany provided particularly good viewing, whereas clouds limited visibility in much of the eastern United States.

While most people observed the Perseids in visible light, David D. Meisel of the State University of New York College at Geneseo and his colleagues viewed it in the infrared. To their surprise, an infrared camera at the University o! Rochester's C.E.K. Mees Observatory saw nothing. Meisel speculates that the blank images indicate that the Perseids represent centuries-old -- not fresh - debris shed by Swift-Tuttle. Over time, he notes, infrared-emitting materials such as water and hydrocarbons would readily evaporate from the debris.

Although NASA delayed launching a space shuttle to avoid any meteor damage and commanded several space vehicles to point away from the shower, the Perseids seem to have made their mark on spacecraft nonetheless. According to Gregory Lange of NASA's Johnson Space Center in Houston, the Russian Mir space station apparently endured some 60 identifiable "hits" that might be attributed to meteoroids striking the craft. And the European Space Agency reported that on the night of Aug. 11, its Olympus satellite suddenly began spinning uncontrollably, possibly in response to a meteoroid impact. To recover the satellite, flight controllers had to use up the remainder of Olympus' already dwindling fuel supply, which forced the agency to end the mission early,
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Title Annotation:unusually intense shower of Perseid meteors on August 11, 1993
Publication:Science News
Article Type:Brief Article
Date:Oct 2, 1993
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