Lightning is a particularly unsettling product of bad weather. It causes more deaths and injuries in the U.S. than either hurricanes or tornadoes do, and it strikes without warning, sometimes with nothing but blue sky overhead. In central Florida, where I live, thunderstorms are a daily occurrence during the summer, and so, ironically, people in the Sunshine State often spend their afternoons indoors to avoid the risk of death from the sky.
Worldwide, lightning flashes about four million times a day, and bolts have even been observed on other planets. Yet despite its familiarity, we still do not know what causes lightning. It is a misconception that Benjamin Franklin solved the puzzle when he conducted his famous kite experiment in 1752.
Although Franklin demonstrated that lightning is an electrical phenomenon, scientists to this day are struggling to understand how thunderstorms generate their charge and how lightning occurs. Some physicists have hypothesized that lightning may actually have an extraterrestrial connection, with cosmic rays--high-energy particles bombarding the earth from space--triggering cascades of speedy electrons in the atmosphere.