November 16, 2009

During the 2009 Leonid meteor shower, you may see anywhere from 30 to 300 shooting stars an hour, depending on whether you're in the right place to see tonight's showy peak, experts predict.

With the highest number of meteors streaking across the skies around 4:45 p.m. ET on November 17, the full Leonids peak will be effectively invisible for viewers in North America and Europe.

In those regions, sky-watchers are advised to venture out away from bright city lights between 2 a.m. and 4 a.m. on the 17th, when they should see 30 to 50 meteors an hour.

(Find out how light pollution has changed our views of the night sky.)

But in Asia, the peak happens during predawn hours, so observers there will have a front row seat for this year's display. (See a NASA map of the 2009 Leonids' peak visibility.)

"Thanks to advances in computer power, since the 1990's we have been able to predict these upswings in activity," said William Cooke, head of NASA's Meteoroid Environment Office.

"This year there is going to be a Leonid strong outburst [during the peak], where the rates may race up to 300 per hour," Cooke said.

"But it may have a surprise in store, as well, and bring an unpredicted short peak at some point, so it's worth it for everyone [all around the world] to go out and look."

Leonids Shower a Temperamental Rock Star

The Leonids are so named because they seem to radiate from the constellation Leo, the lion, which rises above the northeastern horizon between 1 a.m. and 3 a.m., depending on your location.

Like other meteor showers, such as the Perseids and the Orionids, the Leonids happen when Earth plows through a trail of debris left in the wake of a comet orbiting the sun.

When a comet gets close to the sun, melting ice releases pieces of dust, most no larger than grains of sand. Earth annually crosses paths with the orbiting debris from some comets, and the grains burning up in our atmosphere create meteors.

(See pictures of the 2009 Perseids.)

Among the annual sky-shows, the Leonids shower is like a temperamental rock star: In most years it delivers a modest show, with rates of about 15 shooting stars an hour.

In other years, however, the Leonids can suddenly erupt in spectacular meteor storms, with rates of more than a thousand meteors an hour.

That's because the trail of comet debris that creates the Leonids is uneven. The parent comet, Tempel-Tuttle, nears the sun every 33 years, leaving behind fresh clumps of material.

"In exceptional cases, the Earth will dive right through a very fresh trail lain down by the comet, and rates will be truly astronomical." said Geza Gyuk, an astronomer at the Adler Planetarium in Chicago.

The Leonids shower of 1833, for example, saw as many as a hundred thousand meteors an hour—equal to an average of 30 meteors a second, Gyuk said.

2009 Leonids: Modest but Still Worth It

For the 2009 Leonids, experts are forecasting a more modest but still notable sky show, as Earth brushes a 62,000-mile-wide (100,000-kilometer-wide) cloud made of debris left behind from cometary passes in 1467 and 1533.

As with any meteor shower, there's no need for fancy optical equipment to enjoy the show, NASA's Cooke added.

"The best way is to use your unaided eyes so that you can take in as much of the overhead sky as possible," he said.

"Simply lie back, arm yourself with some warm blankets and hot chocolate, and just look straight up."

Andrew Fazekas
for National Geographic News