Each November, the earth's orbit takes it close to dusty flotsam left behind by the comet Tempel-Tuttle, resulting in a celestial show. "Our planet glides through the debris zone every year," explains Bille Cooke of NASA's Marshall Space Flight Center. "It's like a minefield. Sometimes we hit a dust trail, sometimes we don't." Astronomers are predicting that the early morning hours of November 19th will be the best time to catch this year's display, which will be mainly an east-coast affair.
In recent years, the Leonids have been particularly impressive because the earth intersected with dense streams of leftover debris from Tempel-Tuttle's 33.25-year orbit around the sun. The 2001 storm saw so-called zenith hourly rates (ZHR)--the number of meteors an observer would see overhead under ideal conditions--of between 1,500 and 3,000 meteors. "This year we're going to brush past two of the trails--no direct hits," Cooke says. The first encounter occurred last week, with shower activity peaking on November 13th. Skywatchers in Japan reported seeing about 100 shooting stars an hour. The next rendezvous (with a stream shed by the comet in 1533) holds more promise for observers in the U.S., although only for those in Eastern locations. In the early hours of November 19th, Cooke predicts meteor hunters will see more than one each minute.
Even though this year's display may not seem as promising as those past, it's still a good idea to look skyward. Cooke notes that the Leonids are definitely ramping down in intensity (predictions suggest that the earth won't intersect a really dense Tempel-Tuttle debris stream again until 2098 or 2131). After a small spike expected in 2006, he says, that's about it for the rest of the century.