Cause of Northern Lights discovered by Nasa

Nasa scientists have discovered what they think causes the Northern Lights, the dramatic, colourful displays seen in the sky seen near the Earth's poles.

By Catherine Elsworth in Los Angeles
Last Updated: 1:29AM BST 26 Jul 2008

Nasa say explosions of magnetic energy occurring about one-third of the way to the moon are responsible for the lights, known as auroras Photo: AP

After a year of studying the mysterious phenomenon, researchers say explosions of magnetic energy occurring about one-third of the way to the moon are responsible for the lights, known as auroras.

Researchers used a network of five Nasa satellites on a mission dubbed Themis to observe a geomagnetic storm in February.

They correlated results with the findings of observatories in Canada and Alaska, which simultaneously tracked the brightening and movements of the northern, aurora borealis, and southern lights, aurora australis. Both moved across the sky at the same time.

"This is a question that people have been after since the beginning of the Space Age," Vassilis Angelopoulos, the University of California-based principal investigator for the Themis mission, told New Scientist.

"The reason it has not been shown up to now is that we didn't have the right satellites at the right positions and the right times."

Mr Angelopoulos said the observed storm about 80,000 miles from Earth was triggered by a phenomenon known as magnetic reconnection when the Earth's magnetic field lines are stretched like rubber bands by solar energy, snap and ping back to Earth where they reconnect, releasing the energy.

It is the release of this stored-up energy that powers the auroras, he said...

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