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Red Sprites
Wed Jan 12, 2005
Listen in RealAudio 
Towers of pinkish light shooting 25 miles high above the tops of thunder clouds. Red
sprites were discovered by accident in 1989 when scientists pointed a low light video
camera at the horizon and left it to run overnight. No two sprites look exactly
alike.
CR: Fundamentally they are generally vertical columns, so sometimes you'll see a
small group of columns like five or six. Often you'll see 40 columns all packed together
like a bunch of trees. But then there have been examples, like a classic one that looks
like a gigantic jellyfish just hanging in the sky.
Red sprites are thought to occur all over the world. Craig Rogers is a New Zealand
physicist who studies sprites in Australia. He says the lights seem to be caused by
the discharge of an electrical field that forms at the top of a thundercloud.
CR: You take the thundercloud charge away very suddenly and that's the lightning. All
of the shielding charge at high altitudes can't go away very fast so you end up with a
large electric field and the light comes from the electric field exciting the molecules.
Basically, jiggling them around, they get excited and release light.
The flicker of a red sprite lasts only a fraction of a second, but it is possible to see one
with the naked eye. They can sometimes be seen from high flying airplanes at night or
ground-based observers watching thunderstorms in which the preceding lightning
flash is out of sight beneath the distant horizon.
Alan Couckell comes to us from Auckland, New Zealand.
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