Thunder is the sound caused by a nearby flash of lightning and can be heard for a distance of only about 10 miles from the lightning strike. Thunder is created when lightning passes through the air. The lightning discharge heats the air rapidly and causes it to expand. The temperature of the air in the lightning channel may reach as high as 50,000 degrees Fahrenheit, 5 times hotter than the surface of the sun. Immediately after the flash, the air cools and contracts quickly. This rapid expansion and contraction create the sound wave that we hear as thunder. The loud thunder that follows the lightning bolt is commonly said to come from the bolt itself. However, the grumbles and growls we hear in thunderstorms actually come from the rapid expansion of the air surrounding the lightning bolt. Thunder is caused by the rapid expansion of the air surrounding the path of a lightning bolt. When the lightning is within sight, we see it first because the speed of sound in air is considerably slower than that of the electron flow. Thus, the sound behaves more like a shock wave than an ordinary sound wave. The shock wave follows the path of the electrons like a fist in a sock. The speed of sound is even more insignificant when compared to the speed of light. The light from the flash reaches us in a fraction of a second, whereas the sound lags along like a snail following an interplanetary rocket.