Saturday, December 15, 2001

What Is The Leonid Meteor Shower?

The week before Thanksgiving, many people enjoyed the Leonid meteor shower, which was one of the heavier showers in recent times. Even more amazing is the journey each meteor takes from its formation to its fiery end.

Meteors are typically small dust particles that originally were part of objects called comets. Comets are icy remnants of when our solar system was forming, large hunks of ice, rock, and dust. Comets occasionally will enter the inner part of the solar system and the heat of the Sun will start to evaporate the ices. The dust contained in the ice that evaporates will be ejected. This dust is called a meteoroid and will range in size from a few microns to several millimeters or larger. Some of the dust will collide with the Earth, typically at speeds on the order of 10 km/s (roughly 22,000 mph) and at a height of roughly 100 km or 62 miles. Larger particles (about a millimeter) will vaporize from the collision and create light, the familiar "shooting star" that people see. This is a meteor. If a particle survives its fiery entry into the Earth's atmosphere and lands, it is then called a meteorite.

What is special about the Leonids (and the Perseids in the summer) is that these are periodic showers that correspond to specific comets. The orbit of the Earth intersects the orbit of two comets, named Comet Swift-Tuttle and Comet Temple-Tuttle. Temple-Tuttle is responsible for the Leonids. The peak of the Leonids always occurs a few years after the comet passes by Earth on its journey around the sun, which is approximately every 33 years. After the peak, the Leonids aren't so spectacular. The reason for this is a large cloud of dust from Tempel-Tuttle follows a little bit behind the comet. When the Earth plows into this dust cloud, a meteor shower is born. The Leonids get their name because the meteors seem to radiate away from the constellation Leo. The Perseids seem to stream away from the constellation Perseus.

Meteors are very fun to go out and watch, but you need to find a dark place, dress warmly (even in summer), find a comfortable place and look up! Meteors can happen all over the sky so the best thing to do is lay back and try and look at as big a chunk of sky as possible. Then you relax and take in the beautiful sight of a teeny piece of dust that has spent billions of years locked up in ice, been thrown into space, and vaporized just for your enjoyment.