About the Leonids
The unpredictable Leonids
Based on past behaviour, a meteor storm was predicted for 1998 or 1999. In the year 1999, some very bright fireballs appeared unexpectedly 18 hours before the predicted maximum. They were associated with a previously unknown dust band which had been shepherded into a narrow stream by Jupiter's gravity. Unfortunately, although there was also a peak in meteor activity at the predicted time, their trails were not very bright and hard to see with the naked eye.
In 1999, although the Earth reached Tempel-Tuttle's orbit 622 days after the comet passed by, it was predicted that the distribution of its dust ribbons would leave a notable display. One encouraging sign was that the 1998 shower was similar to that of 1965, the year before the storm of 1966. Most astronomers were not expecting a comparable display in 1999, but a spectacular show was not ruled out.
It was foreseen that activity would reach a peak on the night of 17 - 18 November, though earlier fireballs were always a possibility. Nothing was to be visible until the 'sickle' of Leo rised above the eastern horizon around 22:30 GMT. At first, the fainter meteors would be swamped by light from the first quarter Moon, but once this set soon after midnight, conditions were thought to be ideal as long as the sky is cloud free.
The maximum activity was predicted to occur around 02:00 GMT on 18 November, at the time when the Earth passed closest to the comet's orbit. At this time, Leo was well above the horizon over Western Europe.
It was also thought that light trails left by fast-moving meteors may be seen in any part of the sky, but, if traced backwards, they would all seem to originate in the same place - the constellation of Leo. However, appearances are deceptive. Although they appear to spread out like spokes of a wheel, the trails are actually parallel to each other. They just seem to splay out because of our viewing perspective, just as railway lines appear to diverge as they come closer to us.
Some scientists predicted that 2000 or 2001 would provide even better viewing opportunities for the Leonids, but no-one was sure if these unpredictable cosmic visitors would live up to expectations.
"We just know from past history that, in the two years after the perihelion of Comet Tempel-Tuttle, there is enhanced activity," said Dr. Walter Flury of the European Space Operations Centre.
"A storm is possible, but these things are very uncertain," he added. "Predictions are based on models of the way material is distributed along the comet's orbit. But the models are quite inaccurate. We just don't have enough information."
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Last Update: 07 Apr 2006