Over the next few years, there are significant prospects for strong displays of Leonid meteors in mid-November. Prediction of Leonid activity has had a rather chequered history, not helped by the events in 1998, but a new theory is able to explain the historical events and should thus be able to make sound predictions for the near future. Whilst these predictions don't suggest Leonids raining from the sky, as in the "storms" of 1833 and 1966, prospects appear good for a moderate storm visible in dark skies from Australia and eastern Asia in 2001, and in moonlit skies over Europe, west Africa and North America in 2002.

What is a meteor?

A meteor results when a small particle (typically millimetres in size for a visual meteor) of dust orbiting the Sun collides with the Earth's atmosphere. The speed of collision is determined by whether it is a head on collision or otherwise and also the acceleration due to the Earth's gravity. Velocities of collision are between 11 and 72 km/sec (40,000 - 260,000 km/hr). At these immense speeds, the particles are intensely heated in collision with atoms and molecules in the upper atmosphere causing both the particle and air surrounding it to glow. This phenomenon is known as a meteor. From this explanation it is clear why the phrases "falling star" or "shooting star", whilst descriptive, can be seriously misleading. Meteors typically "burn up" at heights around 90 km but for a typical Leonid meteor having a near head-on collision speed of 71 km/sec, the height is typically over 100 km.

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