Aurora Borealis. Green Aurora Borealis or Northern Lights display over a forest. Aurorae are caused by the interaction between energetic charged particles from the Sun and gas molecules in the upper atmosphere (about 100 kilometres up). A stream of charged particles,called the solar wind,flows out into space continuously from the Sun at speeds of 400-500 kilometres per second. On reaching Earth the charged particles are drawn by Earth's magnetic field to the poles,where they collide with the upper atmosphere and cause excitation in the gas molecules. This excitation is released by the molecules as light. Photographed at Fairbanks in Alaska,USA | |
Licence : | Droits gérés |
Crédit: | Science Photo Library / Fh, Jack |
Taille de l’image : | 3130 px × 4759 px |
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