Astronomy Picture of the Day

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http://apod.nasa.gov/apod/astropix.html

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2014 October 13
Sprite Lightning in Slow Motion
Video Credit: H. H. C. Stenbaek-Nielsen (U. Alaska, Fairbanks), DARPA, NSF Explanation: What causes sprite lightning? Mysterious bursts of light in the sky that momentarily resemble gigantic jellyfish have been recorded for over 25 years, but their root cause remains unknown. Some thunderstorms have them -- most don't. Recently, however, high speed videos are better detailing how sprites actually develop. The featured video is fast enough -- at about 10,000 frames per second -- to time-resolve several sprite "bombs" dropping and developing into the multi-pronged streamers that appear on still images. Unfortunately, the visual clues provided by these videos do not fully resolve the sprite origins mystery. They do indicate to some researchers, though, that sprites are more likely to occur when plasma irregularities exist in the upper atmosphere.

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