In compiling this list, we looked at several false beliefs about thunder and lightning. For example, the notion that lightning never strikes twice is doubly wrong. First, about a third of the time, individual lightning bolts strike more than once at a single go [source: NASA]. Second, the same spots -- skyscrapers, for example -- can and do receive multiple strikes per year. So do some people: Ranger Roy Sullivan of Shenandoah National Park, for example, was struck by lightning on seven separate occasions [source: Dunkel]. Ouch.
But the counting rule can be counted on, because it's based on physics: Light travels a lot faster than sound, and the speed of sound in the atmosphere is a known quantity. According to the lore, after seeing a lightning flash, you should count the number of seconds that pass before you hear the thunder. Every five seconds equates to a mile of distance between you and the storm. The math makes sense: At sea level and around 68 F (20 C), sound travels through the atmosphere at around 1,129 feet per second (344 meters per second). Thus, for every five seconds between lightning and thunder, the sound travels 5,645 feet (1,720 meters), or roughly a mile and some change [source: NOAA]. If nothing else, you can use the trick to figure out if the storm is moving toward you or away.