Last Leonid Show of Nearly a Century
Nov. 18, 2002 -- Late tonight and early tomorrow morning, a collision between Earth's atmosphere and a cluster of comet debris will produce a flurry of shooting stars that won't be matched for nearly a century.
If news of the Leonid meteor shower sounds familiar, that's because Earth also brushed through the debris of comet Tempel-Tuttle last year, making it a dazzling night for stargazing as the dust bits burned up in the atmosphere in bright flares.
It's unusual that Earth passes through enough clumps of dust to produce a good storm two years in a row — usually it misses or passes through gaps in the dust cluster — but calculations show we're heading for an even denser clod this year than last year.
And it will be the last big Leonid storm for a long time. Carefully plotted charts of the comet's trail and Earth's projectory show there won't be another significant Leonid meteor shower until 2099.
There's just one problem: A full moon will brighten the backdrop and diminish the storm's splendor.
Avoiding Moonlight
"The rates of falling stars will probably be higher than last year, but with the full moon the 'wow' effect may be comparable to last year," said Peter Brown, a professor of physics and astronomy at the University of Western Ontario.
Peter Jenniskens, an astronomer with the SETI Institute and NASA Ames Research Center NASA, is optimistic the moon won't sour the display. He says the showers this year are going to be three times heavier than last year's and so even if the moon obscures half the meteor streaks, it will still be better than the 2001 showers.
"Just don't look at the moon," Jenniskens advises. "It will be low in the sky anyway so just try and keep it out of your view by blocking it with a tree or your house."
The Leonid's are named after the constellation, Leo, where most of the shooting stars appear to originate in the night sky. Earliest accounts of the meteor shower date to the beginning of the 10th century when reports described a night when the "stars fell like rain," according to amateur astronomer Gary Kronk. He says similar descriptions surfaced for the next several centuries at roughly 33-year intervals in written records of Asian, European and Muslim cultures.
It wasn't until 1833 when astronomers noted the meteors in the November display appeared to radiate from one area of the sky. That led them to realize later that the storms were created when the elliptical orbits of Earth and the comet trail intersect.
The comet trail is regularly refreshed as the comet, Tempel-Tuttle, which is made up of ice and dirt, passes near the sun every 33.3 years. The encounter heats up the comet so it releases a trail of dust. This year Earth is heading for dust clusters left by the comet in 1767 and 1866.
Even the tiniest bits of dust make a bright show as they cross our path.
High-Speed Collisions
"The faintest Leonid you can see is around a 10th of a millimeter across and the brightest is usually no more than 1 millimeter across — or about a couple times the thickness of a human hair," said Bill Cooke, a senior scientist at NASA Marshall Space Flight Center. A fireball of a comet, which can momentarily shine as bright as the planet Venus, is about 9 millimeters in diameter, or about the size of a marble.
How can something so small produce a flash so bright? Speed. The comet's dusty trail and Earth orbit the sun in opposite directions, increasing the intensity of their collision. As a Leonid crashes into Earth's upper atmosphere it is screaming at about 45 miles per second or about 200 times the speed of sound. At that speed the meteor's mass and speed is converted into heat and light as it grates against the molecules of the atmosphere.
People in the United States and Europe are expected to get the best view of this year's show. If the weather cooperates, Cooke expects people could see a meteor streak about once every 6-10 seconds, even amid the glare of the full moon.
When to Watch
Those on the East coast will get two chances to watch the Leonid's. Between 10:30 p.m. and 11:30 p.m. ET, Earth is due to encounter the less dense dust cluster left behind in 1767. Although this first cluster will have fewer meteors, watch for some fireballs. Because Earth's atmosphere will be colliding with the dust cluster at a shallow angle, these Leonid's are expected take longer to burn up and so will leave longer tails.
Those on the West coast will miss the chance to see this first storm since they will still be at the other side of the Earth from the comet cluster during the collisions. But they will have a longer viewing of the storm's peak.
The biggest part of the storm is expected around 5:30 a.m. ET or 2:30 a.m. Pacific time on Tuesday morning. Those on the West Coast should be able to see more meteors since daybreak will cut into the viewing time of those in the East.
Of course, in order to see anything, clear weather is required. And since scientists are better at predicting meteor showers than rain showers, it's uncertain exactly who will have the best view. If there is clear night sky, Jenniskens, who will be in an airplane flying between Spain and Nebraska to watch the shower, argues there's no better reason to skip some sleep.
"This will be the last one for a long, long time," he said. "If you miss it, you'll have to settle for hearing other people tell stories about it for the rest of your life."