The night of Monday November, 18, sees the annual return of the Leonid meteor shower.

This is one of about a dozen such showers which are seen from our region each year. But what makes the Leonids more eagerly anticipated than most is that the display of meteors, or shooting stars, promises to be rather exceptional.

What are Leonids?

Most meteor showers occur when the earth passes through the trail of dust and ice left by a comet. The Leonids are no exception, the comet in question being 55P/Tempel-Tuttle.

This comet orbits the Sun every 33 years. It reached its closest approach to the Sun (perihelion) in February 1988.

As the Earth passes through the trail left by the comet, so dust particles burn up as they enter the Earth’s atmosphere leaving a trail or ‘shooting star’. The closer the comet is to the Sun the more debris it leaves behind. And the closer we are to that trail, the better the display is likely to be.

Since 1988 displays have become increasingly spectacular. Until then meteor rates were only 10 to 15 per hour. But in 1998 this rose to more than 250 per hour whilst in 1999 the meteor ‘storm’ peaked at 3700 per hour.

In 2000 activity reduced to a peak of 480 per hour. Activity increased last year although skies remained generally cloudy across the West Country.

But astronomers have had some success with forecasting the likely peaks of these storms and optimism is high for 2002. They predict a peak of between 2000 and 5000 per hour, occurring around 4 AM on the 19th.

What can people expect to see?

Assuming skies remain clear (a big assumption in this part of the world) just what can people expect to see?

After about 11:30 PM there will be the opportunity to see ‘grazers’ - those Leonids which are not dropping into the Earth’s atmosphere, but merely grazing it.

Richard Angwin - Wiltshire weather is his expertise.

These are likely to be reddish in appearance as they advance from east to west across a large part of the celestial dome.

The radiant is the point from which the meteors appear to originate. This lies in the constellation of Leo (which looks like a backwards question mark).

Leo rises in the eastern sky after midnight. As it does so the Leonids will travel shorter and shorter distances as they plunge into the Earth’s atmosphere.

During this period their colour is expected to change to white or blue-white. Some may even have a greenish tinge.

How to observe the Leonids

Keen observers are likely to be watching the night skies from about midnight onwards on Monday night.

Remember to find a spot which gives a full view of the sky and which suffers from as little light pollution as possible. (Unfortunately the moon will be almost full so the skies will not be as dark as one would wish.)

Look towards the east, though not directly at the radiant.

If skies are clear it is likely to be very cold, so plenty of layers of warm clothing are a must.

An all-night vigil, or at least an early alarm call, will be worth the effort as predictions for coming years suggest a big decrease in Leonid activity.

If the weather does let us down, yet again, then do not despair. The December Geminids could also provide us with a sight to remember.

Richard Angwin
Points West Weatherman