High-speed footage of red sprites above a thunderstorm. Sprites are high-altitude electric discharges that are formed above powerful thunderstorms. This footage shows that the flash of lightning in the cloud occurs immediately before the appearance of the sprite. These are column sprites, or C sprites, which are triggered by positive lightning, although their formation is not fully understood. They occur in the ionosphere, some 50-90 kilometres in altitude, and move downwards from their origin at speeds of over ten million metres per second, sometimes approaching 10% of the speed of light. Filmed from Colorado, USA.