Skywatchers hope to give thanks for more than turkey this year.
Early in the morning this Sunday, the Leonid meteors will streak across the Northern Hemisphere. It is the most famous of all meteor showers, appearing each year in mid-November. Observing their arrival has been an annual ritual for more than a century.
But what will put stargazers flat on their backs is the fact that every third of a century, for about five Novembers in a row, the Leonids erupt in a nighttime display unrivaled in the heavens.
November 1998 presented a celestial bombardment that lasted 18 hours, hence the heightened sense of expectation this year as the shower falls within the five-year bracket of a great show. It's the difference between seeing some shooting stars (nothing to underappreciate, mind you) and bursts of luminescence that make Fourth of July celebrations seem like lightning bugs in the woods.
The galactic debris that will light up the night sky is residue trailing from the comet Tempel-Tuttle. The Earth passes through different parts of this dust stream, which is itself moving through space. This double interaction is the reason meteors are more visible and more numerous some years than others. The comet orbits the sun and makes its closest approach to our star every 33 years.
Astronomers plot the Leonids' radiant, or point of emanation, from the constellation Leo (hence their name). In the Northern Hemispere, at their peak, they should be directly overhead.
Bear in mind that a Leonid meteor is a solid particle traveling at 155,000 m.p.h. as it flames out on entry into the earth's atmosphere.
Icing on the cake: no moon Nov. 17 and 18. And, please - no clouds!
For peak viewing times see www.space.com/scienceastronomy/astronomy/leonids_2001.html.