Streams of dust

Meteors, the technical name for shooting stars, are caused by the debris of the solar system - small fragments of material, mostly no larger than a grain of sand, which burn up as they enter Earth's atmosphere at high speed.

Leonid meteors, so called because they appear to come from a patch of sky in the constellation Leo, are dust particles that have come off Comet Tempel-Tuttle.

Most of this dust is still following the comet fairly closely in space, so we get the best showers when the comet is nearby, as it was earlier this year.

A comet is a flying mountain-sized snowball of rock and ice. During each pass near the Sun, the comet heats up and sheds pieces of ice and rock.

This debris continues to orbit the Sun as streams of small rocky particles. When the Earth intersects such a stream, a meteor shower occurs.

Dust cloud

Comet Tempel-Tuttle takes 33 years to complete an orbit around the Sun, and Earth ploughs through its main dust cloud when it returns to our vicinity every 33 years.

In the years when this happens, a strong shower or storm can take place. In the years in between, a very small number of Leonid meteors are seen in mid-November.

The Leonids are one of a number of meteor showers that take place regularly each year. The most famous are the Perseids in August. The Orionids, a shower in late October each year, are caused by dust from Halley's Comet.

Looking ahead to 1999, Comet Tempel-Tuttle will still be relatively nearby and some astronomers are predicting that the Leonid meteor display could be better next year than this.

If that were to happen, then Europe is expected to be the ideal location.

Picture courtesy of Tony Farnham, Lowell Observatory