Series showing how new camera technology is revealing the inner workings of the Earth's most spectacular natural wonders. Dr Helen Czerski examines the extraordinary new images - from eyewitnesses, scientists and film-makers - that are transforming our understanding of how and why these phenomena form. In this episode she 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 3 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.