UFOs : A recent explaination

As read @ Space.com
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.