Mysterious UFO sightings may go hand in hand with a puzzling natural phenomenon known as sprites — flashes high in the atmosphere triggered by thunderstorms. The dancing lights have appeared above most thunderstorms throughout history, but researchers did not start studying them until one accidentally recorded a sighting on camera in 1989. "Lightning from the thunderstorm excites the electric field above, producing a flash of light called a sprite," said Colin Price, a geophysicist at Tel Aviv University in Israel. "We now understand that only a specific type of lightning is the trigger that initiates sprites aloft."