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Perseid meteor track (lower right) in the night sky over Santorini, Greece. The Perseids meteor shower reaches its peak around 12 August each year. Meteor tracks, also known as falling or shooting stars, are caused by tiny dust grains entering the Earth's atmosphere from space. Meteor showers occur regularly each year when the Earth crosses the orbit of a comet and its debris enters the atmosphere. The Perseid shower is associated with the Swift-Tuttle comet. Santorini is an island in the southern Aegean Sea, south-east of the Greek mainland. Photographed on 12 August 2013. (KEYSTONE/SCIENCE PHOTO LIBRARY/BABAK TAFRESHI, TWAN/SCIENCE PHOTO LIBRARY)