Dear Tom,
Our neighbor says thunder comes from clouds banging together, but I know it is from lightning. How does that happen?
— Jason Strakosh, age 8
Dear Jason,
Weather myths have always been used to provide quick but often erroneous explanations for weather phenomena. Thunder was once associated with the activities of mythological beings (Thor hammering on his anvil, for example) or with the clouds themselves (rubbing or banging together), but we now understand that thunder is the sound generated by lightning. A bolt of lightning, usually less than a half-inch in diameter, heats the air through which it passes to at least 50,000 degrees in a few thousandths of a second. That heated air expands explosively and then immediately contracts upon cooling, creating the sound waves that we hear as thunder.