A series of frames animated to show the dispersal of a Leonid meteor in the early hours of 19 November 2001. Credit: Cheng Huang-Ming Astronomers in western Europe will be looking up at the sky on the morning of the 19 November, observing the Leonid meteor shower which at its peak this year may produce up to 120 meteors per hour.

All the meteors will seem to come from the same point in the sky, or radiant, in the constellation of Leo, hence the name Leonid.

It will be possible to see meteors associated with the Leonid Shower from about the night of 15 November until 20 November after 2130, when the radiant rises above the horizon.

The best chance of seeing the outburst of meteors in the UK will be at 0445 GMT on 19 November.

The absence of the Moon from the sky will make it much easier to see the fainter meteors, with the best view to be had far away from the lights of towns and cities.

The Leonid meteors are associated with comet Temple-Tuttle, which most recently passed close to the Sun in February 1998. The Earth's orbit passes close to the comet’s orbit each year in November and during this time the Earth collides with particles of cometary debris that follow the comet's orbit.

After this year no further outbursts are expected until the end of the 21st century so this really is the last chance to see the Leonids at their best.

Changing orbits

A half-hour exposure of the sky in the early morning hours of 19 November 2001. The image shows more than 100 Leonid meteors, all of which appear to emanate from the radiant in the constellation of Leo. Image: Cheng Huang-Ming During the 1998 passage of the Leonid meteors astronomers were surprised by many very bright fireballs, which came 24 hours before the expected maximum. This led David Asher (Armagh Observatory, UK) and Robert McNaught (Australia), to produce a new theory as to how the orbits of debris from successive passages of the comet change with time. Their theory was brilliantly proved in 1999 when they predicted a peak in the number of meteors accurate to within one minute. In outbursts in the following three years their models also performed strongly – their predictions were out by no more than 30 minutes.

In 2002 the gravitational field of the planet Jupiter shifted much of the cometary material away from the Earth, so no more outbursts are expected for nearly 100 years.

Watching meteors

With patience, meteors can be seen on any clear night of the year and most are caused by particles no bigger than grains of sand, which collide with the Earth’s atmosphere at up to 70km per second (157,000 mph) and burn up. Fireballs are caused by meteors a few centimetres in diameter and can leave tails that persist for several minutes.

Unlike many astronomical objects, observers need no special equipment to view meteors. Weather permitting, the sensitivity and wide field of view of the human eye are perfect for watching the Leonids and so to see this historic shower all observers need to do is watch the sky for a few minutes.