Last year, astronomers and stargazers were treated to a display that reached up to 4,000 meteors per hour. The annual light show is caused by the passing of Comet Tempel-Tuttle, a huge ball of primordial ice and dust thought to have been orbiting the Sun for at least a thousand years. The comet swings through the inner Solar System every 33 years, laying down a trail of dust as it goes. It was last here in 1988. The Leonids are caused when the Earth passes through the dusty debris that follows the comet's orbit.
Most particles are no bigger than a grain of sand.
These hit the Earth's atmosphere at up to 70km per second. More impressive fireballs are meteors that are just a few centimetres in diameter.