Whenever there ‘s a thunderstorm, we can always see a flash of lightening, and several seconds later there follows a loud clap of thunder. But if we see the lightning first, does it mean it really comes first, or is it just an illusion?
About 2,300 years ago, Aristotle thought that thunder occurred when trapped air was forced out of clouds, and that lightning followed the thunder when this released air burned. So according to Aristotle, lightning occurred after thunder and it only appeared to precede it because we see it first. Then, the general belief changed, and lightning was thought to occur first, obviously because we see it first.
In fact, lightning and thunder occur at about the same time. When opposite charges build up inside clouds or between clouds and the ground, there occurs an incredibly hot electrical discharge, called lightning. The air around the discharge is heated almost instantaneously to about 50,000 °F, five times the temperature of the sun ‘s surface. When the air is heated so quickly, a violent expansion creates a shockwave in the air around it, similar to that of an explosion. When this wave travels through the air, it carries vibrations to our ears and we perceive them as the sound of thunder.
Still, if they occur at the same time, why do we see lightning first? It ‘s merely a matter of speed. They occur at the same time, but the speed of light is higher than that of sound. Light travels through air at about 186,000 miles every second, while sound is much slower, moving about 1,000 feet in that same second (the speed may vary depending on temperature and the amount of water vapor in the air). A sound wave travels through the air as vibrating molecules bump into their neighbors, transferring energy.