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."
Researchers have detected the flashes between 35 and 80 miles (56-129 km) from the ground, far above the 7 to 10 miles (11-16 km) where usual lightning occurs. Sprites can take the form of fast-paced balls of electricity, although previous footage has suggested streaks or tendrils.
The cause or function of the flashes remains murky, but Price suggested that they could explain some of the UFO reports which have cropped up over the years. That might provide some solace for UFO enthusiasts disappointed by human-caused hoaxes in the past.
Both jetliner pilots and astronauts have previously reported sightings of sprites, along with a different but equally mysterious phenomenon known as blue jets.
Price and his colleagues have focused on "winter sprites" which appear only in the northern hemisphere's winter months. Their remote-controlled roof-mounted cameras can spot thunderstorms producing sprites far out over the Mediterranean Sea.
Triangulation techniques have also allowed the researchers to calculate the dimensions of the sprites.
"The candles in the sprites are up to 15 miles high, with the cluster of candles 45 miles wide it looks like a huge birthday celebration!" Price said.
Sprites may have some effect on the Earth's ozone layer, but researchers suspect that the global impact is small.