Thunder is caused by the rapid expansion and contraction of air surrounding a lightning bolt. When lightning passes through the air, it heats the air to extremely high temperatures-up to about 50,000 degrees Fahrenheit (around 30,000 degrees Celsius), which is several times hotter than the surface of the sun. This intense heating causes the air to expand explosively, creating a shockwave as the surrounding cooler air is rapidly compressed. Immediately after, the air cools and contracts quickly. This rapid expansion followed by contraction produces the sound waves we hear as thunder

. The initial sound of thunder is often a sharp crack or clap, caused by the shockwave near the lightning channel. The rumbling sound that follows is due to the sound waves coming from different parts of the lightning channel at varying distances. Forked lightning can cause overlapping shockwaves that bounce off clouds and terrain, creating continuous rumbles

. In summary, thunder is the audible result of the sudden and violent heating of air by lightning, which causes rapid air expansion and contraction, producing the characteristic booming and rumbling sounds of a thunderstorm