Monday, September 20, 2010

Aurora Borealis

courtesy of National Geographic :
the Northern Lights are one of nature's most spectacular visual phenomena,
and in this time lapse video they provide a breathtaking display of
light, shape, and color over the course of a single night in Norway

From Spaceweather

Solar activity continues to increase after a two-year solar minimum that ranks among the century's deepest.
The return of sunspots and a resurgent solar wind is good news for aurora watchers, who are seeing some of the best displays since ~2006.
With increased solar activity and as the Summer slowly wanes into Autumn, the Northern Lights are beginning to dance across the skies.

The Aurora Borealis, also called the Northern Lights, are beautiful curtains of light created when fast electrons from the solar wind slam into the rarefied gas of the upper atmosphere. The mechanism of action is similar to the way electrons in a television generate specks of light when they impact the phosphor-coated inside of the screen.
However, the physics of the Aurora Borealis are complex, and not perfectly understood.
The energy of certain types of aurora probably derives from a dynamo effect of the interplanetary (solar wind-caused) magnetic field against the Earth's magnetic field.
This is similar to the way electricity can be generated by rotating a magnet within an electromagnetic coil.

The aurorae are green or faint red in color, produced by re-emission from atmospheric oxygen.
Atmospheric nitrogen sometimes produces very faint blue/violet aurorae.
Some of the most magnificent pictures of aurorae have been taken from the Space Shuttle or International Space Station, which views the phenomenon from an angle impossible from the ground.
The Aurora Borealis is most easily observed about 1500 miles (2400 km) from the Earth's magnetic poles.
A southern variant also exists, called the Aurora Australis, but this is rarely observed because it mainly occurs in the oceans around Antarctica.
The Earth's magnetic poles are located about 11° away from the geographical poles.
In the north, the magnetic pole is located just north of Canada, meaning the Aurora Borealis is easily observable from places like Fairbanks, Alaska.
Rarely, during magnetic storms and coronal mass ejections (super solar-flares), the Aurora Borealis becomes much more intense, and can be visible as far south as Boston.
In 1856, a coronal mass ejection produced aurorae so strong that one could read a book at night in New York using the light produced.

The Aurora Borealis have long been subjects of mythology and superstition.
Scandinavians once thought they were produced by the reflections of huge schools of herring.
In Scotland, they were called the "merry dancers".
Gold miners in Alaska believed they were reflections of the greatest mother lode.
Until the advent of scientific satellites, many of the theories about the aurorae were very speculative.
Even today, our understanding is not perfect, but is steadily improving.

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