Thunder is the sound made by lightning. The process of lightning zipping through the air causes a sudden heating of the air to a temperature estimated at 40,000 degrees Fahrenheit. This causes an explosive expansion of the air, which produces a shock wave. When you hear thunder, there is often a loud bang followed by a traveling rumble. These two sounds are the initial expansion followed by the shock wave propagating through the air.
Light from the flash is delivered to your eyes instantaneously, but the sound travels much slower, at roughly one mile in about five seconds. Using this differential, it is possible to estimate lightning’s distance. Count the number of seconds from the flash to the boom. Each second represents roughly one-fifth of a mile, or about a thousand feet. If you count to two, you can estimate the lightning struck about two thousand feet away.
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