K JAYARAM / SCIENCE PHOTO LIBRARY K JAYARAM / SCIENCE PHOTO LIBRARY
Contrail over Alps. View of a condensation trail from an aeroplane in the sky over snow-covered mountaintops. At high altitudes the water vapour emitted as a product of a jet engine's combustion raises the relative humidity of the surrounding air past saturation point and the resulting water droplets freeze into visible ice crystals. Photographed near Titlis mountain, Uri Alps, Switzerland.
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