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Aurora over Yellowknife
Intense auroral activity flooded the night with shimmering colors on February 24, 2011—captured here from a lodge near the city of Yellowknife in northern Canada. 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.