for National Geographic News
Blink during a thunderstorm and you may miss the unusual phenomenon of "sprites"—resplendent bursts of light that, for less than a second, burn brighter than Venus.
These brief explosions, which can outshine everything except for the sun and moon, are so fleeting, that scientists still don't know much about how they work.
(See related: "Huge Mystery Flashes Seen in Outer Atmosphere" [June 25, 2003].)
So in a recent study, a group of physicists used an ultra high-speed digital camera to record sprites in unprecedented detail—10,000 frames per second.
"We realized that all these branches and long luminous features that we saw in the sprites, that they didn't really exist," said lead author Hans Nielsen, a physicist at the University of Alaska, Fairbanks.
"It's sort of like you take a time exposure on a highway, and then all the tail lights of the cars make long streaks in the image."
Instead, sprites are made up of tiny bright balls that speed through the middle atmosphere at one-tenth the speed of light, said study co-author David Sentman, a physicist at the University of Alaska. These sprite balls shine five times brighter than Venus.
(See a video of the sprites.)
Now You See It ...
Many researchers believe the sprites' short duration allowed them to escape notice for so long.
"You see this flash in the sky and then you think 'No, that can't be!" Nielsen said.
Scientists did know, however, that sprites occur during active thunderstorms. They are electronic discharges that make the air above glow a luminous red, similar to how fluorescent bulbs burn.
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