Thunder is the sound produced by the rapid expansion and contraction of air surrounding a lightning bolt. When lightning strikes, it heats the air to temperatures as high as 30,000 degrees Fahrenheit, causing the air to expand quickly. This sudden expansion creates a shock wave that travels through the atmosphere, resulting in the sound we hear as thunder. The sound of thunder can vary in intensity and duration, depending on factors like distance from the lightning strike and atmospheric conditions. It can range from a low rumble to a sharp crack. People often associate thunder with storms, particularly those involving lightning and rain.