Sprites or red sprites are large-scale electric discharges that occur in the mesosphere, high above thunderstorm clouds, or cumulonimbus, giving rise to a varied range of visual shapes flickering in the night sky. They are usually triggered by the discharges of positive lightning between an underlying thundercloud and the ground.
Sprites appear as luminous red-orange flashes. They often occur in clusters above the troposphere at an altitude range of 50–90 km (31–56 mi). Sporadic visual reports of sprites go back at least to 1886 but they were first photographed on July 4, 1989, by scientists from the University of Minnesota and have subsequently been captured in video recordings many thousands of times.
