There is an easy way to estimate how far away a thunderstorm is. After you see a flash of lightning, count off the seconds until the thunder is heard. Divide the number of seconds by five. The result gives the approximate distance (in miles) to the thunderstorm.

The reason why this estimation works is simple. When a bolt is generated, light and sound (thunder) are produced nearly at a same instant. Light travels so rapidly that it reaches the observer almost instantaneously. Its travel time is only

seconds.

seconds.

Thus, the time interval between seeing the flash and hearing the thunder is about 5 seconds for every mile of travel. The time it takes the light to reach the observer is very small. Therefore it can be ignored. That is why only the time it takes for the thunder to reach the observer is used to estimate how far away a thunderstorm is.