Observing the Leonid Meteor Shower

Nov. 15, 2007 — The annual Leonid meteor shower will peak early Sunday morning, Nov. 18. This reliable, but sparse, annual shower usually produces about five to 15 meteors per hour under dark skies.

To see the shower (if the weather is clear), go outside, lay down in a sleeping bag or in a lawn chair, face northeast and look about halfway up in the sky. The meteors will appear to stream out of the constellation of Leo the Lion (hence the name Leonids). Normally, the shower is strongest in the early morning hours (between 1 a.m. and 5 a.m.) when Leo is nice and high in our sky. You will not see any Leonid meteors before 11:30 p.m. when Leo rises in our sky.

A meteor shower occurs when the Earth passes through debris that has been shed by a comet. Comets are very dirty snowballs, consisting of water ice, methane ice, ammonia ice and little bits of rock, dust and metal. As the comet approaches the sun and warms up, the ice sublimates (goes from a solid to a gas), thus releasing the little bits of rock and dust trapped in the ice. These particles continue in the same orbit as the comet and spread out behind it.

Every Nov. 17-19, the Earth passes through the debris stream left from Comet Temple-Tuttle on its 33-year orbit around the Sun. The debris stream is hitting the Earth head-on at a speed of about 40 miles per second. As the particles burn up in the Earth's atmosphere, they leave the visible streak we call a meteor. The tremendous velocity of the Leonid meteor particles results in bright, fast meteors in the sky. However, the stream is sparse, and so an observer typically sees only five to 15 Leonid meteors per hour.

If, however, the Earth passes directly through the stream of particles left behind by the comet on a previous passage around the sun, we can get a good outburst. In 1833 and 1966, the Earth passed through two very dense streams just behind the comet resulting in a meteor storm with hundreds of thousands of meteors per hour.

Since the comet was last in the inner solar system in 1998, there is essentially no chance of us passing through a dense stream right behind the comet this year.

—  By Ed Murphy, associate professor of astronomy