Mr. Collins: Have you ever noticed that during a storm, you see the lightning first and hear the thunder later? They actually happen at the same moment. Lightning heats the air around it so quickly that the air expands with a boom. That boom is thunder.

Mr. Collins: So why don't we notice them together? Because light travels much, much faster than sound. The flash reaches your eyes almost instantly, but the sound takes about five seconds to travel one mile.

Mr. Collins: That gives you a way to estimate how far away the lightning is. When you see a flash, count the seconds until you hear the thunder. Then divide by five. If you count ten seconds, the lightning was about two miles away.

Mr. Collins: One more thing. If you can hear thunder at all, you're close enough for lightning to reach you. So remember the rule. When thunder roars, go indoors.