<p>Stars wheeling across the sky seem to cut through a fiery <a id="yr7o" title="aurora" href="http://science.nationalgeographic.com/science/space/universe/auroras-heavenly-lights.html">aurora</a> in a recently released long-exposure picture taken in western <a id="f1ha" title="Sweden" href="http://travel.nationalgeographic.com/travel/countries/sweden-guide/">Sweden</a>.</p><p>Auroras can appear in different colors depending on the types of gases in the atmosphere and where these gases are. Auroras happen when energized particles form the sun interact with air molecules and give them extra charge. These "excited" molecules then emit light. Oxygen, for example, can create auroras in yellow-green to red, while nitrogen emits light in blues and purples.</p>

Star-Struck Aurora

Stars wheeling across the sky seem to cut through a fiery aurora in a recently released long-exposure picture taken in western Sweden.

Auroras can appear in different colors depending on the types of gases in the atmosphere and where these gases are. Auroras happen when energized particles form the sun interact with air molecules and give them extra charge. These "excited" molecules then emit light. Oxygen, for example, can create auroras in yellow-green to red, while nitrogen emits light in blues and purples.

Photograph by P-M Heden, TWAN

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