A Danish astronaut has captured the best ever images of rare, blue flashes

ESA/NASA

Scientists don't know much about the mysterious, powerful electric discharges that sometimes occur in the upper levels of the atmosphere in conjunction with thunderstorms. The first photograph of the phenomenon—which can occur as high as about 90km above the surface of the Earth and are known variously as sprites, pixies, elves, or jets—was only taken from Earth in 1989.

Fortunately for scientists interested in these storms, the International Space Station offers an excellent vantage point at an altitude of about 400km. So Danish researchers devised a "Thor experiment"—named after the hammer-wielding Norse God—to study the phenomenon. As part of the experiment, an astronaut on board the station would image thunderstorms under certain conditions, and these observations would be correlated with data collected by satellites and ground-based radar and lightning detection systems.