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Welcome to Brain Stuff from howstuffworks.com, where smart happens.

Marshall Brain

Hi, I’m Marshall Brain with today’s question, how does the aurora borealis, or the Northern Lights, work? The aurora borealis has always fascinated mankind and people even travelled thousands of miles just to see this amazing light show in the earth’s atmosphere. The auroras, both surrounding the northern magnetic pole and the southern magnetic pole, occur when highly charged electrons from the solar wind interact with elements in the earth’s atmosphere.

Solar winds stream away from the sun at speeds of about one million miles per hour. When they reach the earth some 40 hours after leaving the sun, they followed the lines of magnetic force generated by the earth’s core and flow through the magnetosphere – a tear-dropped shaped area of highly charged electrical and magnetic fields.

As the electrons enter the earth’s upper atmosphere, they encounter atoms of oxygen and nitrogen at altitudes from 20-200 miles above the earth’s surface. The color of the aurora depends on which atom is struck and the altitude of the meeting. Green auroras mean that an oxygen atom up to 150 miles in altitude has been hit by an electron. Red auroras mean that an oxygen atom above 150 miles in altitude has been struck. A blue aurora means that a nitrogen atom up to 60 miles in altitude has been struck. And a purple or violet aurora means that a nitrogen atom above 60 miles in altitude has been struck.

All of the magnetic and electrical forces react with each other in constantly shifting combinations. These shifts and flows can be seen as the auroras appear to dance, moving along with atmospheric currents. The auroras generally occur along the auroral ovals, which center on the magnetic poles of the earth and roughly correspond to the Arctic and the Antarctic circles. There are times, though, when the lights are further south, usually when there’s a lot of sun spots.

Sun spot activity follows an 11-year cycle and the next peak will occur in 2011 and 2012, so opportunities to see auroras outside their normal range should be good. There are many stories about sounds associated with auroras, but there are no recordings of these sounds. Scientists can’t agree on what would produce sounds during an aurora.

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