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What are the Leonids?


The Leonids are named after the area of sky from which they seem to originate - the sickle-shaped constellation of Leo (the Lion). The famous meteor shower appears each year between 15 and 19 November, but usually the numbers are few - perhaps 20 or 30 per hour at peak times. However, every 33 years or so the shower strengthens dramatically, with thousands of glowing meteor trails illuminating the early morning skies.

[Illustration courtesy of Sky & Telescope]

The most recent peak in the number of Leonids took place in 1999, when the shower produced more than 3,000 meteors per hour. Although the numbers were much lower last year, astronomers are optimistic that the best is yet to come.

Most spectacular of all were the events of 1833 and 1966, when the sky was awash with the incandescent streamers from more than 100,000 shooting stars per hour.

These periodic bursts of activity are tied to the motion of comet Tempel-Tuttle, which returns to the vicinity of the Earth and the Sun every 33 years. Like a gigantic chimney travelling through space, the comet belches out a dense cloud of gas and dust each time that its icy nucleus vapourises in the heat of the Sun. When the Earth ploughs headlong through this cloud, frictional heating incinerates any debris that enters the atmosphere, producing the annual Leonid light show.


Detailed studies of the dust trails from each passage of Tempel-Tuttle indicate that the Earth may pass through several ancient streams this year. If the predictions are correct, there will be two peaks on 18 November - one at 10:01 GMT (11:01 CET) and another at 18:19 GMT (19:19 CET). The best places to observe the second of these apparitions should be eastern Asia and (hopefully) cloud-free Australia.

[Illustration courtesy of Sky & Telescope]

© ESA Science 2001.