<p><strong>An aurora illuminates the skies over Fairbanks, Alaska, in a 2009 picture released this week.</strong></p><p>Auroras occur when large numbers of charged particles from the sun encounter Earth's magnetic shield. Most of these particles get corralled toward the Poles, where they slam into atmospheric gases such as nitrogen and oxygen.</p><p>(See <a href="http://news.nationalgeographic.com/news/2012/03/pictures/120301-auroras-northern-lights-space-science-borealis/#/aurora-borealis-northern-lights-february-mountains_49402_600x450.jpg">"New Aurora Pictures: Earth-Shield Cracks Spur Surprises."</a>)</p>

Aurora Over Alaska

An aurora illuminates the skies over Fairbanks, Alaska, in a 2009 picture released this week.

Auroras occur when large numbers of charged particles from the sun encounter Earth's magnetic shield. Most of these particles get corralled toward the Poles, where they slam into atmospheric gases such as nitrogen and oxygen.

(See "New Aurora Pictures: Earth-Shield Cracks Spur Surprises.")

Photograph by Yuichi Takasaka, TWAN

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