Earthgrazers
Leonid meteors will take their time arriving the night before the peak. Wherever you are on Earth, you're viewing location has to rotate into the stream of space dust that causes the Leonids. The shooting stars will appear to emanate from a point in the sky known as the radiant, which for the Leonids happens to be in the constellation Leo (hence the name).
No knowledge of this is needed to find an earthgrazer. Just go out and look to the east. The timing depends on where you live. Figure mid-evening for high northern latitudes, such as Canada; late evening hours for mid-northern latitudes, as in most of the United States; and after midnight for equatorial regions and the Southern Hemisphere.
What might you see?
"When the radiant lies near the horizon the Leonid meteors cannot penetrate far into the Earth's atmosphere," explains Robert Lunsford of the American Meteor Society. "At this time they are only able to skim the upper atmosphere."
These earthgrazers, as scientists call them, often last several seconds and can span a great distance of the sky, Lunsford said.
To see an earthgrazer, you'll need an unobstructed view of the eastern horizon.
Later, as Earth continues rotating, the Leonid radiant moves higher into the sky, along with its host constellation and all the stars. Meteors will strike the atmosphere at a more direct angle, Lunsford explains, creating shorter paths. But the paths will still span much of the sky, so you don't need to face East. In fact, the best views will be everywhere but directly East.
Just go out, look up.
Fireballs
Most Leonid meteors are created by sand-sized grains of dust that vaporize about 60 miles up due to the heating caused by Earth's atmosphere. But Tempel-Tuttle, the comet that has left all this Leonid raw material in space, also deposits a few larger chunks of itself each time it swings around the Sun (which it does every 33 years).
A comet fragment the size of a marble can generate a glorious fireball of light as it burns up. Instead of slicing through the atmosphere like a small bit of dust, such a pebble sometimes goes splat upon meeting up with a certain density of air.
"The Leonids can have fireballs, but they're not especially noted for them," said Bill Cooke, a meteor researcher at NASA's Marshall Space Flight Center. Cooke said the number of fireballs each year depends in part on which streams of cometary debris Earth plows through.
In 1998, observers noted several fireballs when the planet moved through a stream that comet Tempel-Tuttle had deposited in the 14th Century. The Sun's radiation had blown much of that ancient dust into a widely dispersed region of space, so the 1998 Leonids did not produce a great number of shooting stars.
But the larger material -- fireball material -- was still relatively concentrated. In fact, Cooke said, scientists are learning that gravity acts on these larger fragments, causing them to be huddled more closely together over time. They call the process "gravitational focusing."