Every year on or about November 17 the Earth passes through the orbit of Comet Tempel-Tuttle. Since comets lose gas and dust each time they orbit the sun, a comet's orbit is dirty–littered with debris. When the Earth passes through this debris, we see an increase in meteor activity as the debris plunges into the Earth's atmosphere and burns up. This increase in activity is known as a meteor shower. The Earth crosses the orbits of several comets in its trip around the sun, and each of these crossing is associated with an annual meteor shower. The two most famous of these are the Perseid Meteor Shower which occurs around August 12 and the November 17 shower, known as the Leonid Meteor Shower, or Leonids for short.
Comet Tempel-Tuttle orbits the sun once every 33 years, so about every 33 years the debris in its path is replenished and we see a corresponding increase in activity. Historically, the Leonids are capable of producing intense activity. This was observed in 1833 when people in the eastern U.S. were awakened by bright flashes in the sky and cries of neighbors. (Some estimates place the activity as high as 30,000 meteors per hour.) Another Leonid meteor storm occurred in 1866, followed by impressive (but not so spectacular) showings in 1899-1900 and 1933. The storm roared back in 1966 with an estimated 100,000 meteors per hour (or about 27-28 per second). Astronomers are guardedly predicting anything from a good to spectacular show this year.
The Leonid meteor shower will probably peak on Wednesday evening, but these predictions have very “plus or minus” times–as much as a day. The predicted peak is for 7 p.m. - 10 p.m. CST Wednesday. NASA is suggesting that people view between 10 p.m. Wednesday evening and dawn Thursday morning local time. If you are up before sunrise Wednesday morning, it might even be worth looking then.
Of course the big excitement is the possibility of a another meteor storm with tens or hundreds of thousands of meteors per hour (as opposed to the typical 10-20 per hour, or a heavy shower of hundreds per hour). If a storm occurs, it will probably be short-lived (a few hours at most) because the debris stream associated with Comet Tempel-Tuttle (the source of the Leonids) is very narrow.
Meteor observing tips from the experts:
Meteors associated with the Leonid shower may be observed in any part of the sky, but they will all appear to radiate from a single point in the constellation Leo (hence the name Leonids). Leo, distinguished by its “backwards question mark” shape, doesn't actually rise until around 12:30 a.m., but even before it is up the meteors can be observed. After midnight is generally better for any meteor shower because you are then on the leading edge of the Earth in its orbit around the sun. (Before midnight, you're riding on the rear window–the only bugs that hit are the ones that catch you from behind. After midnight you're on the windshield–you pretty much get everything that can't outrun you.)
NASA has some good information. Start at http://science.nasa.gov. At last check there were links to at least five different articles on the Leonids, and each of those articles contains additional links. Published articles on the Leonids may be found in the March 1999 and November 1999 issues of Sky and Telescope or the November 1998 issue of Astronomy magazine.
Get out and enjoy!Back to main Leonids page