Weather permitting, a dark, moonless night should set the stage for a particularly vivid sky show tonight, the peak of the annual Leonid meteor shower. (Read about last year's Leonid meteor shower.)
Sky-watchers should be able to spot even the faintest Leonid meteors, with up to about two dozen meteors an hour lighting up the night in the wee hours of Saturday.
The Leonids are so named because they seem to radiate from the constellation Leo, the Lion, which in the Northern Hemisphere this time of year rises around local midnight, and by 3:00 a.m. is high in the eastern sky. (See a Leonid viewing diagram.)
Like most meteor showers, the Leonids are caused by Earth plowing through a comet's dust trail, in this case comet Tempel-Tuttle, which completes a circuit of the sun every 33 years. When the comet gets close to the sun, melting ice releases pieces of dust, most no larger than grains of sand. (See asteroid and comet pictures.)
During a meteor shower, Earth "is like a car speeding through a cloud of insects on the freeway: The windshield side of the car slams into the insects, leaving streaks on the glass that you can see," said Ben Burress, staff astronomer at the Chabot Space and Science Center in Oakland, California.
"If you look out the back window of the car, you won't see bug streaks, because that's the direction the car is coming from," he said.
Meteor Storms Can Create Mega-Shows
Though this year will likely see a good Leonid meteor show, it can get even better: Sometimes the Leonids produce meteor storms that set off as many as a few hundred so-called shooting stars an hour during the peak.
The last big Leonid storm occurred in 2002, with 3,000 meteors falling an hour at the height of the action. But the granddaddy of all meteor storms—and the root of Leonids' mythical status among generations of sky-watchers—was the 1833 storm, when as many as a hundred thousand shooting stars occurred in one hour.
"But since it's been about ten years since the last [big Leonid] storm, we should be in a quiet period" until the comet again approaches the sun in two decades, Burress said.
In general, "It's amazing to think that these pieces of dust are often specks of material left over from the formation of the solar system, captured by the comet and transported into our part of the solar system," he added.
"They are often 4.5-billion-year-old bits, and we see them vaporize in a flash!"