Lightning is an atmospheric discharge of electricity that occurs when negative and positive particles inside storm clouds separate. It forms when the negatively charged bottom of clouds induces a positive charge on the ground, causing a spark to jump between them. Benjamin Franklin famously experimented with lightning by flying a kite during a storm and collecting a spark from the key attached to the kite string. Lightning can heat the air around it to temperatures hotter than the sun's surface and strike at speeds over 130,000 mph.