Sun struck



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The reward for those endless winter nights is a view like this.

Photos copyright Jan Curtis, University of Alaska Fairbanks, Geophysical Institute; courtesy The Aurora Page, Michigan Technological University.




The aurora's light is released when electrons change their orbits in atoms high in the atmosphere.Look up!
Northern lights. Just the name is enough to conjure up the unearthly sky shows that grace the polar regions.

The Northern lights -- the aurora borealis -- are centered around the north Magnetic Pole, in northern Canada. The southern lights -- the aurora australis -- are similarly focused on the southern magnetic pole.

Broad, greenish-white strokes behind some conifer trees. We asked Neal Brown, a scientist from Alaska who delights in explaining the aurora borealis, what accounts for these light shows. He started by telling us that several streams of particles from the sun can create the lights. The constant, low-level solar wind operates 24/7, delivering a flow of electrons and protons from the sun, creating a full-time but rather faint aurora.

The real fireworks occur when a big mass of junk is ejected from the sun by a solar flare or a coronal mass ejection creating a giant stream of fast-moving particles.

One big generator
Lots of stuff happens when solar particles near the Earth, due to electromagnetic interactions. Because charged particles cannot cross the lines of a magnetic field, charged particles that enter Earth's magnetic field are channeled toward an end of the field -- near the north or south magnetic pole.

As they enter the tenuous atmosphere high above Earth, these fast-moving charged particles excite atoms they strike, raising electrons into higher orbits. The aurora's light comes from the emission of a photon -- light particle -- that occurs when an electron drops back to a lower orbit. More on the aurora.

photo of northern lights: Look closely and you'll see the Big Dipper peeking through this wispy aurora.Since solar storm particles are moving, they are an electric current. When they move in Earth's changing magnetic field (which rotates once a day), the result is an electric generator that can produce an enormous current -- millions of amps.

That changing electrical current produces, in turn, a changing magnetic field. And because changing magnetic fields induce electrical currents in any conductor, major solar flares can cause currents to develop in spacecraft, power lines and pipelines.

And that's why solar eruptions make operators of these expensive machines as skittish as a long shot at the Kentucky Derby.

What have they been writing about the dangers of the sun?



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