Scientists expose mystery behind northern lights

[July 25, 2008]  CAPE CANAVERAL, Fla. (AP) -- Scientists have exposed some of the mystery behind the northern lights. On Thursday, NASA released findings that indicate magnetic explosions about one-third of the way to the moon cause the northern lights, or aurora borealis, to burst in spectacular shapes and colors, and dance across the sky.

The findings should help scientists better understand the more powerful but less common geomagnetic storms that can knock out satellites, harm astronauts in orbit and disrupt power and communications on Earth, scientists said.

A fleet of five small satellites, called Themis, observed the beginning of a geomagnetic storm in February, while ground observatories in Canada and Alaska recorded the brightening of the northern lights. The southern lights -- aurora australis -- also brightened and darted across the sky at the same time.

These auroral flare-ups occur every two or three days, on average.

A team led by University of California, Los Angeles, scientist Vassilis Angelopoulos confirmed that the observed storm about 80,000 miles from Earth was triggered by a phenomenon known as magnetic reconnection. Every so often, the Earth's magnetic field lines are stretched like rubber bands by solar energy, snap, are thrown back to Earth and reconnect, in effect creating a short circuit.

It's this stored-up energy that powers the northern and southern lights or, in other words, causes them to dance, according to Angelopoulos.

An opposing theory has these geomagnetic events occurring much closer to Earth, about one-sixth of the way to the moon. More Themis observations are needed to resolve the debate, said David Sibeck, NASA's project scientist.

"Finally, we have the right instruments in the right place at the right time, and it's allowed scientists to be able to make the necessary observations to settle this heated debate once and for all," said Nicola Fox, a Johns Hopkins University scientist who was not involved in the study.

At present, about 20 of these geomagnetic storms are being analyzed. Scientists hope to eventually learn, via this project, more about the bigger solar storms that occur about 10 times a year and can lead to far more expansive and prolonged northern and southern lights.

The five Themis spacecraft -- a NASA acronym standing for Time History of Events and Macroscale Interations during Substorms -- were launched aboard a single rocket last year.

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On the Net:

NASA: http://www.nasa.gov/themis/

[Associated Press; By MARCIA DUNN]

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