Sprites are large-scale electrical discharges that occur high above a thunderstorm cloud, or cumulonimbus, giving rise to a quite varied range of visual shapes.
They are triggered by the discharges of positive lightning between the thundercloud and the ground.
The phenomena were named after the mischievous sprite (air spirit) Puck in Shakespeare's A Midsummer Night's Dream.
They normally are colored reddish-orange or greenish-blue.
There are hanging tendrils below and arcing branches above their location, which can be preceded by a reddish halo.
They often occur in clusters, lying 50 miles (80 km) to 90 miles (145 km) above the Earth's surface.
Sprites were first photographed on July 6, 1989 by scientists from the University of Minnesota and have since been witnessed tens of thousands of times.
Sprites have been mentioned as a possible cause in otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.