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Aurora Borealis Explained.

Sunspot activity causes the northern lights, or aurora borealis, yet it is not unique to the north. When the solar wind(a stream of particles and gas from the sun) comes in contact with the earth's magnetic field, spectacular light shows result near both magnetic poles. At the southern pole, aurora australis mirrors the northern display.

Solar flares occasionally explode from the sun's surface causing the best auroras. Other auroras result from energy release from the sun's dark holes during its normal today rotation, pausing a solar wind.

After a three-day space journey, the solar wind particles hit earth's magnetic field, painting shimmering bands, pulsing ribbons or curtains of color across the sky. Sometimes they drape overhead like an umbrella while at other times they merely light up the horizon with a green glow.

The colors of the aurora result from the solar flare or wind's charged particles coming in contact with various gases at different levels in the earth's atmosphere. Light yellow-green is most common and results from oxygen contact at about 60 miles above the earth. Blue or violet colors appear when the aurora contacts nitrogen in the atmosphere. The brilliant and rare all-red aurora glows from high-level oxygen 200 miles above the earth.

The elusive black aurora continues to baffle scientists. Professor Charles Deer at the University of Alaska Fairbanks Geophysical Institute calls it a reverse aurora. Deer describes it as an area of the sky where auroral activity blankets the sky in a green glow, yet there appears black ribbons interspersed. Black auroras form shapes like corkscrews, smoke rings or giant amoebas.

Many observers say they can hear the aurora sing. Yet, scientists have not been able to substantiate this.

Auroras vary throughout the night during an auroral storm, yet seem best about midnight. The best viewing areas in the world fall within range of the auroral oval. According to Deer, the doughnut-shaped ring hovers around 67 degrees magnetic latitude north.

The upcoming solar maximum occurs in an 11-year solar activity cycle. Scientists predict numerous sun spots and solar flares during the years 2000-2003. As activity increases the auroral ring grows, producing more frequent and brilliant displays seen farther south.

For the best auroral watching, Deer recommends February or March. He also recommends choosing a time close to the new moon for darker skies. He states that the time between 10 p.m. and 2 a.m. is the best window of opportunity for viewing auroras.

Auroral information compiled from the University of Alaska Fairbanks Geophysical Institute Web site.
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Publication:Alaska Business Monthly
Article Type:Brief Article
Geographic Code:1U9AK
Date:Dec 1, 1999
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