for National Geographic News
Beginning late tonight and stretching into the predawn hours of Thursday morning, more than 20 meteors an hour will streak across the sky, bringing a burst of spring joy to meteor shower enthusiasts.
Known as the Lyrids, the shower appears to emanate from a point in the sky, or radiant, just west of the constellation Lyra, which contains the bright star Vega. (Lyra is found near the more familiar constellation Cygnus, also known as the Northern Cross.) (See star chart.)
In nearly all the world's time zones, the Lyrids' radiant rises above the horizon at around 11 p.m. If the skies are clear and dark, sky watchers should begin to see a steady stream of shooting stars about an hour later, as Earth turns into the meteor stream, according to astronomers.
"If you are brave enough or hardy enough to stay awake to the wee hours of the morning, the higher the radiant gets, the better," said William Cooke, a meteor-shower expert with the Space Environment Group at NASA's Marshall Space Flight Center in Huntsville, Alabama.
The radiant reaches maximum altitude just before dawn on Thursday morning. The anticipated peak for meteor activity is 11 p.m. ET tonight, but stargazers in the United States will not see much until the radiant is higher, Cooke said.
Peter Jenniskens is an astronomer and meteor-shower expert with the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California. He said this year should be an excellent one in which to see the Lyrids, since the moon will be absent during the shower, making for a dark sky.
"It's not a very intense shower, not as intense as the Perseids. But it happens after a long time of very low [meteor-shower activity] in the spring. This sort of starts the meteor season," Jenniskens said.
Though named the Lyrids because the meteors appear to radiate from the constellation Lyra, the meteors have nothing to do with Lyra. Rather, they are bits of dusty debris shed by comet Thatcher.
Thatcher is a so-called long-period comet, because it takes about 450 years to make a single trip around the sun. Any comet with an orbit longer than 200 years is considered a long-period comet. Thatcher last made its closest approach to the Sun in 1861.
When Thatcher makes a close approach to the Sun, debris is cooked off. Initially, this debris forms a cloud of dust that travels along with the comet.
But when the comet reaches the furthest point in its orbit from the sun and then rounds the bend on its return, the extra kick that some dust particles received during their prior ejection makes them move even farther out. Thus, these dust particles lag behind the comet when they fall back to the sun, forming a trail in the comet's path.
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