Thunder is the loud noise that follows a flash of lightning. Many ancient cultures believed that thunder was the sound of the gods roaring in anger when they were displeased. Today, scientists know that thunder is caused by lightning. A stroke of lightning heats a narrow path of air to extraordinarily high temperatures—up to around 55,000 °F (30,000 °C). The intense heating creates a sharp increase in air pressure. The rising pressure generates a shock wave that moves outward in all directions. As the shock wave travels through the air, it produces the sound waves that we hear as thunder.
Thunder has many different sounds. Sound waves coming from various parts of a lightning stroke reach an observer at different times, resulting in a rumbling noise. A lightning stroke can fork into many branches, which produce a sharp crackling sound. Lightning that strikes nearby produces a sharp clap or crack followed by a loud bang.
Loading the player...Thunder clap and rumble
The sound of thunder reaches us after we have seen the lightning. The sound lags because light travels 186,282 miles (299,792 kilometers) per second, but sound travels only 0.211 miles (0.340 kilometers) per second. The number of seconds between seeing a lightning flash and hearing the thunder, divided by five, yields the approximate distance of the lightning stroke from the observer in miles. Divided by three, it gives the approximate distance in kilometers.
See also Lightning; Shock wave; Thunderstorm.
