<p><strong>A curtain of green <a href="http://science.nationalgeographic.com/science/space/universe/auroras-heavenly-lights/">auroras</a> ripples over hoodoo rock formations near Drumheller, Canada, early Monday, Labor Day in the U.S. The same night, similar shows enlivened skies over many high-latitude countries across the Northern Hemisphere.</strong></p><p>Last Friday a solar flare exploded off the sun, launching a giant cloud of charged gas—a <a href="http://education.nationalgeographic.com/education/multimedia/solar-flares-cmes/">coronal mass ejection</a>, or CME—toward Earth. About 48 hours after<a href="http://www.nasa.gov/"> NASA</a>'s<a href="http://www.nasa.gov/mission_pages/sdo/main/index.html"> Solar Dynamics Observatory</a> had detected the eruption, the CME, travelling faster than a million miles an hour, slammed into Earth's magnetic field, sparking the auroras.</p><p>When a CME, or solar wind, enters the upper atmosphere, its charged particles smash into and break up gas molecules, which give off energy in the form of the so-called northern lights (or in the Southern Hemisphere, southern lights).</p><p>The colors a sky-watcher sees depend on the type of gas being hit and how high it is. For example, the green aurora pictured was the result of oxygen-atom collisions about 60 to 120 miles (100 to 200 kilometers) up.</p><p>(More<a href="http://news.nationalgeographic.com/news/2011/08/pictures/110810-auroras-northern-lights-space-science-sky-night-borealis/"> pictures: "Multicolored Auroras Sparked by Double Sun Blast."</a>)<em></em></p><p><em>—Andrew Fazekas</em></p>

Electric Hoodoos

A curtain of green auroras ripples over hoodoo rock formations near Drumheller, Canada, early Monday, Labor Day in the U.S. The same night, similar shows enlivened skies over many high-latitude countries across the Northern Hemisphere.

Last Friday a solar flare exploded off the sun, launching a giant cloud of charged gas—a coronal mass ejection, or CME—toward Earth. About 48 hours after NASA's Solar Dynamics Observatory had detected the eruption, the CME, travelling faster than a million miles an hour, slammed into Earth's magnetic field, sparking the auroras.

When a CME, or solar wind, enters the upper atmosphere, its charged particles smash into and break up gas molecules, which give off energy in the form of the so-called northern lights (or in the Southern Hemisphere, southern lights).

The colors a sky-watcher sees depend on the type of gas being hit and how high it is. For example, the green aurora pictured was the result of oxygen-atom collisions about 60 to 120 miles (100 to 200 kilometers) up.

(More pictures: "Multicolored Auroras Sparked by Double Sun Blast.")

—Andrew Fazekas

Photograph by Darryl Reid

New Aurora Pictures: Solar Flare Sparks "Snakes," "Spears"

Sparked by a Friday solar flare, Sunday night's green-and-purple sky show seemed to glimmer with snakes, spears, and a fiery phoenix.

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