Leonids 2000: Spectacular display or damp squib?
9 November 2000One of the most exciting things about meteor showers is their sheer unpredictability. Just when astronomers think they know all about a particular shower, something happens to spring a surprise. One of the least predictable of the annual meteor showers is the Leonids, which appears each year around 16-18 November.
The Leonid shower is named after the constellation of Leo - the region of sky from which the meteors (also commonly known as shooting stars) appear to originate. However, the meteors actually come from a tenuous stream of dusty debris (known as meteoroids) expelled by Comet 55P/ Tempel-Tuttle during centuries of passing close to the Sun.
This debris spreads out along the comet's orbit, and every November the Earth passes through or close to the cosmic dust trail. As the dust- and sand-sized particles burn up in Earth's atmosphere, some 100 streaks of light an hour may grace the skies.
Sometimes, a more intense downpour, strong enough to qualify as a meteor storm, illuminates the night sky. Leonid storms occur roughly every 33 years, when the Earth passes through a particularly dense trail of debris that lies close to the comet. A major Leonid storm occurred in 1966 and last year a peak rate equivalent to around 2700 meteors an hour occurred early on the morning of 18 November.
Significant advances in predicting Leonid activity have been made over the past 2 years by closely observing shower activity. However, astronomers still do not fully understand how comets spread dust grains along their orbit and how this debris disperses over years and centuries.
"We need as many observations as possible in order to modify our models of the Leonid dust stream," said ESA scientist Jean-Pierre Lebreton.
So What Will Happen This Year?
Carola Göckel and Rüdiger Jehn from the European Space Operations Centre (ESOC) in Germany predict a peak rate of up to 900 Leonids per hour just before 08:00 GMT (09:00 CET) on 17 November. They expect the intensity to be almost half as great as last year's Leonid storm over Europe. They also predict a smaller peak of about 300 around midday GMT (13:00 CET) on 18 November. Unfortunately, if they are correct, then neither maximum will be visible in Europe.
UK astronomers David Asher and Robert McNaught foresee a "normal" display of up to 100 meteors per hour, although there may be two peaks in activity as the Earth passes close to dust streams released from the comet in 1733 and 1866. These peaks are predicted for 03:44 GMT (04:44 CET) and 07:51 GMT (08:51 CET) on 18 November. If these predictions are correct, the first maximum should be visible in Western Europe, although the second increase in activity will be hidden by daylight (except in North America).
An alternative model by Ignacio Ferrin suggests that the Earth will miss the centre of the Leonids' dust trail by a small margin, but there is still a reasonable chance of a significant shower. According to Ferrin, the maximum activity is likely to be around 09:20 GMT (10:20 CET) on 17 November, when the meteor rate may peak at 3500-5000 per hour - with a slight possibility that it may briefly soar to 50 000 per hour. If this is true, then Europe will miss out on the main firework display, but North Americans could be in for a wonderful spectacle.
U.S. meteor specialist Joe Rao, favours rates of 250 to 500 per hour on the morning of 17 November, although he admits that the morning of 18 November could be this year's "Leonid Wild Card."
The bad news is that, whenever the peak arrives, only the brightest of the fireballs will be easily visible. Many of the fainter meteors will be lost in the glare of the Moon, which is only five days past Full and sitting close to Leo in the night sky.
For anyone hoping to see this year's shower, the best solution is to look away from the Moon and towards the Plough, or to stand where the Moon is hidden from view by a building or other obstruction.