Starwatch: meteors and their icy origins in the heart of a comet

The Orionids meteor shower will brighten our skies later this month. What are meteors and where do they come from?

Spend an hour or so under a clear moonless sky and we will be unlucky not to spot a small number of meteors. Some are slow and graceful while others may be swift and glimpsed only out of the corner of our eye.

They occur when meteoroids, usually dusty clumps no larger than a grain of rice but moving in excess of 20km per second, disintegrate in the atmosphere at altitudes between 75 and 100km.