Auroras are natural different colored light displays, which are usually observed in the polar zone's night sky. In northern latitudes, it is known as the aurora borealis, named after the Roman goddess of the dawn, Aurora, and the Greek name for north wind, Boreas. It often appears as a greenish glow (or sometimes a faint red), as if the sun were rising from an unusual direction. The aurora borealis is also called the northern [polar] lights, as it is only visible in the North sky from the Northern Hemisphere. The aurora borealis most often occurs from September to October and from March to April.

Its southern counterpart, aurora australis/southern [polar] lights, has similar properties. Australis is the Latin word for "of the South".
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You can find more information at this link and many others like it.
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http://en.wikipedia.org/wiki/Aurora_(astronomy)
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