Dangerous Earth- Lightning (3 of 6)

Dr Helen Czerski examines the hottest natural phenomena on the planet - lightning. Bolts of lightning five times hotter than the surface of the sun strike our planet over three million times every day - and yet we still know little about this deadly force of nature. Now, specialist photography is revealing how lightning travels through the air, high-speed cameras are unlocking the secrets of upward lightning that's triggered by our urban landscapes, and scientific expeditions are capturing rare images of intense electrical discharges over 80 kilometres wide.