thunder

A loud, dry noise or rumble that accompanies the flash of lightning. It is due to the violent expansion of the air that takes place in the discharge channel crossed by the lightning bolt, as a consequence of the sudden heating that occurs there, with temperatures reaching up to 30,000°C. Thunder is heard with a delay relative to the sight of the flash, because the speed of sound (333 m/s) is much lower than that of light (300,000 km/s). If we count the seconds elapsed between seeing the flash of light and hearing the boom or dull roar, and divide them by 3, we will know approximately how many kilometers away the storm is. By repeating the operation every so often, we will know whether the storm is approaching or moving away from us.