High-speed footage of a gigantic blue jet, a high-altitude electrical event associated with thunderstorms. Blue jets are a rare electrical event, and appear at the tops of thunderclouds and extend to the ionosphere, some 40-70 kilometres above the Earth. It is thought that their blue colour is due to ionisation of molecular nitrogen in the air. They travel upwards from the cloud tops at speeds of up to 100 kilometres per second, far faster than the more common lightning below, and they usually last less than a second. This is the first ever piece of footage of a gigantic blue jet connecting the troposphere with the ionosphere, filmed over a thunderstorm over the ocean off Puerto Rico, in September 2001.