2. Blue Sprites: Ethereal Dancers of the Upper Atmosphere
Another amazing kind of blue lightning seen far above thunderstorms are blue sprites. Usually found in the mesosphere, these ethereal, jellyfish-shaped flashes of light span 50 to 90 kilometres. Strong positive cloud-to- earth lightning strikes set sprites off unlike blue jets.
The blue hue of sprites comes from the electrical discharge exciting nitrogen molecules. Blue light is emitted as these molecules revert to their ground state. Often found in bunches and spanning many kilometres in diameter, sprites provide an amazing show in the nighttime heavens.
Fascinatingly, sprites were originally expected to exist in the 1920s, but they were unintentionally seen on camera only in 1989. Researchers have been working to solve the riddles of these enigmatic events by means of ground-based and space-based instrumentation since then.