Thunder

Thunder is the sound produced when lightning passes through the air. Lightning is an extremely powerful electrical discharge that heats the air along its path to very high temperatures for a brief moment.

This rapid heating causes the air to expand quickly. The expansion creates a shock wave that spreads through the air; to the human ear it sounds like a crack or a long rumble. For this reason thunder and lightning occur simultaneously: one is a visual phenomenon, the other is sound.

Hearing Thunder

The sound does not arrive at once. Lightning is a long channel through the air, and each part produces sound that reaches the ear at different times. This means thunder can sometimes be a sharp crack, sometimes a rolling sound lasting several seconds. Mountains and clouds also reflect and extend the sound.

Estimating Distance

Light reaches the eye instantly, but sound is much slower. When someone counts the seconds between seeing the lightning flash and hearing the thunder, they can estimate the storm's distance: roughly each second corresponds to less than one kilometre. This method is an approximate estimate, not a precise measurement.

Safety and Protection

Thunder itself causes no harm—it is only sound. The danger comes from lightning. Standard advice includes staying in a sturdy building or closed vehicle when thunder is heard, staying away from isolated trees, tall buildings, and open water, and waiting some time after the last sound before going outside.

Culture and Climate

Thunder and rain usually occur together, especially during seasons of heavy rain and standing storm clouds. In Somali culture and others, the sound of thunder is seen as a sign of approaching rain and is tied to proverbs and cultural narratives that speak to changes in weather.