Leonid meteors. Optical time-exposure image of Leonid meteors (streaks) against a starfield containing the Milky Way (band across centre). Meteors (shooting stars) are tiny dust particles which enter the Earth's atmosphere at high speeds. They are heated by air resistance, making them visible as streaks of light. The Leonid shower occurs each year for about 2 days around 17th November, when the Earth crosses the debris produced by the comet Tempel-Tuttle (55P). Photographed in 2001.