Lightning is a natural electrical discharge in the atmosphere. Studies estimate that roughly 30 to 100 cloud-to-ground and cloud discharges occur every second worldwide—about 9 million per day. How lightning initiates inside thunderclouds remains an active research topic; work published in Nature Scientific Reports and elsewhere suggests that relativistic runaway electron avalanches (RREA) and electric fields around 1.8–2.0 kV/cm play a role in triggering discharges.

Thunder is the sound produced when the lightning channel heats the surrounding air to around 20,000–30,000 K in a fraction of a second. This rapid heating creates a shock wave that travels outward at roughly 3,000 m/s before decaying into an acoustic wave. By the time it reaches your ear, it travels at the speed of sound (about 343 m/s at sea level), which is why you hear thunder after the flash.

Lightning can produce X-rays and gamma radiation and exhibits time scales from tens of nanoseconds to nearly a second for a full discharge. The map above shows live detections from the Blitzortung community network.