NASA Explains Dancing Northern Lights

Scientists have discovered a secret to the Northern Lights, one that exposes some of the mystery behind the aurora borealis for the first time. Using a fleet of satellites, NASA researchers at the Goddard Space Flight Center observed explosions of magnetic energy that cause sudden brightenings and rapid movements that appear as a green-colored hue.

NASA launched THEMIS Aurora Observing Satellites in early 2007 to help scientists learn more about geomagnetic storms that can knock out satellites, harm astronauts in orbit and disrupt power and communications on Earth. Scientists use five satellites and a network of 20 ground observatories located throughout Canada and Alaska to observe and collect data in their ongoing mission.

The new findings show, for the first time, something called magnetic reconnection which triggers the onset of substorms, or auroral flare-ups, to occur every two to three days. This causes the Earth's magnetic field lines to be stretched by solar energy, much like an outstretched rubber band drawn too far. After reaching a point of maximum resistance, these lines eventually snap and throw back the energy to Earth, where the lines finally reconnect. Since every action has an equal and opposite reactions, the result in a short circuit that sends waves back from wence they came.

"As they capture and store energy from the solar wind, the Earth's magnetic field lines stretch far out into space. Magnetic reconnection releases the energy stored within these stretched magnetic field lines, flinging charged particles back toward the Earth's atmosphere," said David Sibeck, THEMIS project scientist in Greenbelt, Md. "They create halos of shimmering aurora circling the northern and southern poles."

It's this stored-up energy that powers the Northern Lights and it's the distribution of that energy which causes amazing shapes and colors. "We discovered what makes the Northern Lights dance," said Dr. Vassilis Angelopoulos of the University of California, Los Angeles. Angelopoulos is the principal investigator for the Time History of Events and Macroscale Interactions during Substorms mission, or THEMIS.

THEMIS is the fifth medium-class mission under NASA's Explorer Program and is being by Berkeley's Space Sciences Laboratory. The program, managed by the Explorers Program Office at Goddard, provides frequent flight opportunities for world-class space investigations in heliophysics and astrophysics.

Related Links: Video: The Story of THEMIS Satellites
NASA THEMIS Mission Site

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