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Watching the northern lights form

Events that spark the skies begin in Earth's magnetic tail

The sudden burst of color seen in the sky as the aurora borealis and the aurora australis has not only dazzled, but has also puzzled. Specifically, scientists have long debated how the brightening is triggered in outer space. Now, a team has identified what caused the sudden flare-ups in the polar auroras last February.

“The findings change our understanding of how the auroras are generated,” says Vassilis Angelopoulos of the University of California, Los Angeles.

Reporting in the July 25 Science, Angelopoulos and his colleagues suggest that when the lines of Earth’s magnetic field reconnect, a large amount of energy spreads through the outer atmosphere, shooting a jet of charged particles toward Earth to light up the polar auroras.

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