The aurora, or northern and southern lights, are often
visible from the surface of the Earth at high northern or southern latitudes.
Auroras typically appear as luminous bands or streamers that can extend
to altitudes of 200 miles (well into the ionosphere).
Northern and Southern
Lights
The following figures
show three examples of the often spectacular visible light display associated
with auroras.
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Southern aurora from the Space Shuttle Endeavor
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Northern aurora over Lake Superior
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Northern aurora over Circle, Alaska
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Here is another image of the southern aurora taken from the Space Shuttle.
The aurora changes with time, often looking like moving curtains of light.
The Cause of Auroras
Auroras are caused by high energy particles from the solar wind that are trapped in the Earth's magnetic field. As these particles spiral back and forth along the magnetic field lines, they come down into the atmosphere near the north and south magnetic poles where the magnetic field lines disappear into the body of the Earth.The delicate colors
are caused by energetic electrons colliding with oxygen and nitrogen molecules
in the atmosphere. This excites the molecules, and when they decay from
the excited states they emit the light that we see in the aurora.
Auroras at Non-Visible
Wavelengths
The collisions of
trapped charged particles with atmospheric molecules causes spectacular
effects in the visible spectrum, but these excited molecules can also emit
radiation in other wavelength bands. The following figures show aurora imaged
in the ultraviolet (UV) and X-ray regions of the spectrum.
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| UV emission from northern aurora observed by the Polar satellite | X-ray emission from northern aurora observed by the Polar Satellite |
These images were
obtained by the NASA Polar Satellite. The X-ray image represents the first
global photograph of an aurora in the X-ray spectrum.
Information supplied by: http://csep10.phys.utk.edu