Mysterious 'sprites' caught on film
The strange bursts of lightning known as sprites, which flash red, white or green 50 miles above Earth during thunderstorms, are very rarely seen.
Indeed, they're so hard to catch on film that pilots had observed them for almost a century before one was accidentally caught on camera in 1989 - and photographs have been few and far between since then.
Now, though, NASA scientists, with help from Japan's NHK television station, have caught them on video following a two-week research project.
Filming at 10,000 frames per second on two separate jets, the team say they've now captured some of the best movies of sprites ever taken. By filming from two jets flying 12 miles apart, the team mapped out the three-dimensional nature of the sprites.
"Seeing these are spectacular," says Hans C Stenbaek-Nielsen, a geophysicist at the University of Alaska.
"But we need the movies, because not only are they so fast that you could blink and miss them, but they emit most of their light in red, where the human eye is relatively blind."
It wasn't easy to know where to look for the sprites. Once a plane found a hot zone, though, they often lucked into filming numerous sprites in a row. The sprite's first flash is usually followed by a break up into numerous streamers of light – and figuring out what causes this divergence is one of the key things researchers hope to gain from these films.
Sprites are believed to be related to lightning, in which a neutrally-charged cloud discharges some of the electricity to ground. Normally, a negative charge is carried from the cloud to the ground - but about ten percent of the time it's a positive charge, leaving the top of the cloud negatively charged and producing a sprite.
The video's here.