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Meteors. Time-lapse image of Leonid meteors and star trails. The meteors are the straight streaks seen against the curved star trails. An amateur astronomer's observatory can be seen at lower right. Meteors are tiny particles of dust which enter the Earth's atmosphere at high speed. Heating from air resistance makes them visible as streaks of light. The Leonid shower occurs each year for two days or so around 17th November, when the Earth crosses the path of debris produced by the Tempel-Tuttle 1886 I comet. Star trails are formed on long exposure photographs by the apparent movement of the stars caused by the Earth's rotation. Photographed in 1998. (KEYSTONE/SCIENCE PHOTO LIBRARY/A. BEHREND/EURELIOS)