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·Astronomy: Observatory - WHERE IN THE WORLD

  Natural Skylight: Astronomy: Natural Skylight - CURTAINS OF LIGHT
Posted on Saturday, December 04 @ 16:23:16 CST by astronomy
  Natural Skylight


The compelling sight of the aurora borealis, or northern lights, has inspired, frightened, and otherwise transfixed people living in Arctic regions for centuries. To the Inuit of North America, the undulating gossamer curtains of light were the play of unborn children, or the torchlight held by the dead to aid the living in winter. Some say that if you whistle gently, the lights will respond by drawing nearer. In Scandinavia, it was once common to use auroras for weather forecasting, and auroras are still called "wind lights" and "weather lights."

Auroras are spawned around the Earth's magnetic poles by activity on the Sun. Generally, the more active the Sun, the more prominent the aurora. Solar activity increases and decreases over about 11 years, with most sunspots and solar flares appearing toward the middle of the cycle. The flares produce tremendous outflows of charged particles that intensity the solar wind. When the particles reach Earth, they excite, or ionize, neutral oxygen and nitrogen molecules in Earth's upper atmosphere. This ionization produces the eerie colored glow that we see as an aurora.

In both the Northern and Southern hemispheres, most auroral activity is confined to high latitudes—the region above 65 degrees. Auroras are commonly seen in Alaska, Canada, and Scandinavian countries, but in the Southern Hemisphere—where the phenomena is called the aurora australis, or southern lights—few inhabited loca-tions are far enough south to see it often. During periods of high solar activity, auroras can extend down to latitudes of 40 degrees or less, and during extreme activity, they may even reach the tropics. One major outburst of solar activity in March 1989 produced auroras that were seen from the Caribbean Sea.

Auroras are usually visible for about an hour, but during peaks in solar activity, they can last all night. For Northern Hemisphere observers, an aurora begins as a dome of reddish or greenish light in the north. The glow eventually shapes itself into a distinctive arc that gradually creeps southward. During its peak, green, red, and blue streamers of light may extend to the zenith and beyond.

Spectacular photographs of auroras can be made using a tripod-mounted camera, fast film, and a wide lens. Simply aim the camera toward the aurora and expose tor 10 to 40 seconds. Color photographs will often reveal subtle colors that the eye does not detect.




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