The Earth is actually passing through two debris streams tonight, and this is old, old comet dust we're encountering.
"Europeans this year are running through the 1767 comet trail," said Yeomans. "North Americans will see meteors from the 1866 orbit."
The first encounter should cause a flurry of meteors over Europe and Africa around 0430 UT. The second encounter favors North Americans who are likely to see an outburst around 5:30 a.m. EST or 10:30 UT. Visit NASA's web site for estimates of best viewing time by location, http://leonid.arc.nasa.gov/estimator.html
Particles shed when the comet's orbit was closest to the sun this trip, which occurred on February 28, 1998, won't be seen for a long, long time, said Yeomans.
When the comet comes closest to the sun, particles are being released at a variety of velocities, leaving a new trail of dust. The trail will be affected by gravity and other factors, and each dust stream evolves somewhat independently. The 1998 particle stream is still hot on the tail of its parent comet, he said.
This is definitely the year to watch. When the comet next passes the sun in 2031 and 2065, the Earth isn't likely to pass through concentrated dust streams because Jupiter's gravitational pull will push the comet farther away from the Earth's orbit.
"We won't see another major Leonid show until the end of the 21st century," said Peter Brown, an astronomer specializing in meteors at The University of Western Ontario.
"This is the last chance for everyone alive now to see the Leonids in their full glory."
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