For the past several years, sky-watchers have awaited mid-November in anticipation of possible strong displays from the Leonid meteor shower. The Leonids are associated with Comet Tempel-Tuttle, which has an orbital period of 33 years, and normally are a rather weak affair, usually producing only ten meteors per hour or less. Around the times that the comet has made its returns, however, the Leonids have often produced extremely intense but brief displays when the rate has reached several tens of thousands of meteors per hour. Strong historical Leonid showers include those that took place on November 13, 1833 -- the famous night when "stars fell on Alabama" -- and on November 17, 1966, when the meteor rate may have exceeded 100,000 meteors per hour in a display which this author, then a young child, was privileged to witness.

Comet Tempel-Tuttle made another return in 1998, and with it has come another series of strong Leonid showers. Almost the entire planet witnessed an impressive shower of bright Leonids in 1998, and an intense shower of 5000 or more meteors per hour was observed from the Middle East in 1999. While there were no especially strong showers in 2000, both North America and Asia witnessed strong showers, again with rates of several thousand meteors per hour, last year.

The art of predicting the time and strength of meteor showers has made great strides in recent years, in large part because of the heavy anticipation of the current series of Leonid showers. The astronomers involved in this process have determined that the Earth's passage by dust trails ejected by Comet Tempel-Tuttle during specific returns in the past is the primary contributor to the Leonid displays we are presently witnessing. Two teams (working independently of each other) have proven to be quite successful in predicting the times and strengths of the recent showers: one team consists of Irish astronomer David Asher and Australian astronomer Rob McNaught, the other team has Finnish astronomer Esko Lyytinen and American astronomer Thomas Van Flandern. Both teams successfully and accurately predicted the times of last year's showers to within a few minutes.

Both teams are predicting that the world will see strong Leonid showers again this year. The Earth will encounter the dust trail from Tempel-Tuttle's 1767 return at around 9:00 P.M. MST on Monday evening, November 18. At that time the constellation of Leo (from which the Leonids appear to radiate) will be below the horizon as seen from most of North America, however central and western Europe, and western Africa, are in prime viewing locations for this display. Both teams are predicting that this particular shower will produce between 1000 and 3000 meteors per hour.

A few hours later, between 3:30 and 3:40 A.M. MST on Tuesday morning, November 19, the Earth should be passing almost directly through the dust trail from Tempel-Tuttle's 1866 return. Almost all of North America, and especially the western United States, is well placed for seeing the resulting Leonid display, with both teams expecting a peak rate in the vicinity of 3000 meteors per hour. It is conceivable that the rate could be even higher than this.

The one significant downside to any potential strong showers from the Leonids this year is that the moon will be nearly full, and the resulting bright sky will wash out many of the dimmer meteors. This will be slightly mitigated by the fact that, around the time of the expected peak display, the moon will be fairly low in the western sky (while Leo is high in the eastern sky), and thus the effects of moonlight can be partially alleviated by viewing from a location where the moon is shielded behind a building or a hill. The moon-brightened sky will nevertheless take its toll on the numbers of meteors that will be seen.

Despite the moonlight, sky-watchers should take advantage of this opportunity to view the Leonids, since this will very probably be the last strong Leonid shower for a long time. During the coming years the Earth does not pass close to any of Tempel-Tuttle's dust trails, and thus starting next year the Leonids will probably be back to their typical ten meteors per hour. And while the comet will make future returns in 2031 and 2065, gravitational tugs by the planets will keep the dust trails from passing anywhere near Earth during those times. Not until the comet's return in 2098, or even possibly the subsequent one in 2131, will the Earth pass close enough to any of the dust trails to produce the potential for another strong Leonid shower.

So, on Tuesday morning, sky-watchers should grab a lawn chair and some warm clothing, lie back, face east, and look -- up. Whatever display we might see on Tuesday morning, we will view it in the knowledge that several generations of humanity will live, and will pass on, before another human eye once again sees an intense meteor shower from the Leonids.