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The Northern Lights

July aurora July aurora
Aurora over Hancock, MI looking north, July 25, 2004, 2:18am
Photos by Claudia Perko

Aurora Borealis is a natural colored light displays in the sky, usually observed at night, in the polar zone of Alaska. Aurora Borealis was named after the Roman goddess of dawn, Aurora, and the Greek name for north wind, Boreas. It often appears as a greenish glow or sometimes a faint red, as if the sun was rising from an unusual direction. The aurora borealis, also called the northern polar lights, because it is only visible in the North sky from the Northern Hemisphere. These lights most often occurs from September to October and from March to April.

What causes these lights?

NASA launched a fleet of five satellites called THEMIS, the Time History of Events and Macroscale Interactions during Substorms to find out what causes the shimmering, ethereal Northern Lights to suddenly brighten and dance in a spectacular burst of colorful light and rapid movement.

Researchers have discovered that an explosion of magnetic energy a third of the way to the moon powers substorms, sudden brightenings and rapid movements of the aurora borealis, called the Northern Lights.

The culprit turns out to be magnetic reconnection, a common process that occurs throughout the universe when stressed magnetic field lines suddenly "snap" to a new shape, like a rubber band that's been stretched too far.

Substorms produce dynamic changes in the auroral displays seen near Earth's northern and southern magnetic poles, causing a burst of light and movement in the Northern and Southern Lights. These changes transform auroral displays into auroral eruptions.

Ground station observations of an aurora
A collection of ground-based All-Sky Imagers (ASI) captures the aurora brightening caused by a substorm. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

Substorms often accompany intense space storms that can disrupt radio communications and global positioning system signals and cause power outages. Solving the mystery of where, when, and how substorms occur will allow scientists to construct more realistic substorm models and better predict a magnetic storm’s intensity and effects.

Artist concept of a substorm Artist's concept of a substorm. Credit: NASA

Artist concept of a THEMIS satellite
Artist's concept of one of the THEMIS satellites in orbit of Earth. Credit: NASA

The THEMIS team’s findings will appear online July 24 in Science Express and August 14 in the journal Science.


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