Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2011 March 25
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Auroral Substorm over Yellowknife
Image Credit & Copyright: Kwon, O Chul (TWAN)

Explanation: Intense auroral activity flooded the night with shimmering colors on February 24, captured here from a lodge near the city of Yellowknife in northern Canada. The stunning sequence (left to right) of three all-sky exposures, taken at 30 second intervals, shows rapid changes in dancing curtains of northern lights against a starry background. What makes the northern lights dance? Measurements by NASA's fleet of THEMIS spacecraft indicate that these explosions of auroral activity are driven by sudden releases of energy in the Earth's magnetosphere called magnetic reconnection events. The reconnection events release energy when magnetic field lines snap like rubber bands, driving charged particles into the upper atmosphere. Stretching into space, these reconnection events occur in the magnetosphere on the Earth's night side at a distance about 1/3 of the way to the Moon.

Tomorrow's picture: naturally so

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