NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Aurora borealis. 12-hour animation mapping the aurora borealis (northern lights, green) over northern Canada and Alaska during a geomagnetic stom on 9 March 2008. The observations were made by 20 all-sky cameras that complement the THEMIS (Time History of Events and Macroscale Interactions during Substorms) system. The blue circles are the overhead areas observed by the cameras. Aurorae occur when charged and energetic particles from the Sun (the solar wind) are drawn by Earth's magnetic field to the polar regions. Hundreds of kilometres up, they collide with gas molecules and atoms, causing them to emit light. The aurorae appear on the animation from east to west as the Earth rotates from west to east under the storm. For this animation with a time stamp, see K003 2440.
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