FactSentinel

Thunder and lightning are not produced at different times. Both result from the same event: a lightning bolt superheats the air along its channel to roughly 30,000 degrees Celsius, about five times hotter than the surface of the sun, in a fraction of a second. This causes the air to expand explosively, creating a shock wave that becomes the sound of thunder. The flash of light and the shock wave begin at essentially the same moment.

The delay between seeing and hearing comes from the different speeds at which light and sound travel. Light moves at about 300,000 kilometers per second, so it reaches an observer almost instantly. Sound travels through air at roughly 343 meters per second, or about one kilometer every three seconds. The farther away the strike, the longer the gap. This is why counting the seconds between a flash and the thunder gives a rough estimate of distance: about three seconds per kilometer, or five seconds per mile.

The misconception likely persists because the delay is so noticeable that it seems to suggest two separate events. The same effect appears in everyday life, such as seeing a distant firework burst before hearing it, or watching a person hit a ball far away and hearing the impact a moment later. Thunder can also seem to rumble for a long time because sound from different points along a long, jagged lightning channel arrives at different times.