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Lightning slices through air, heating it to about 60,000ºF (five times hotter than the sun’s surface!). The heated air quickly expands in an outward explosion, but then contracts as it cools. The rapid back and forth movement of air particles as it expands and contracts produces sound waves that we know as thunder.

Thunder and lightning always occur at the same time, but light travels faster than sound so we see lightning before hearing thunder. Every five seconds between the two phenomena is roughly equivalent to a mile. Thus, counting the seconds between a lightning bolt and a thunderclap, one can calculate the distance to the storm.

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