what makes thunder sound

Thunder is caused by the rapid expansion of air surrounding a lightning bolt due to the extreme heat generated by the lightning flash. The lightning can heat the air to temperatures as high as 54,000°F (30,000°C) in a fraction of a second, causing the air to expand explosively. This rapid expansion creates a shock wave or sonic boom, which travels through the air and is heard as thunder. The initial sharp crack or bang occurs closer to the lightning strike, while the following rumbling sounds come from shock waves traveling from farther points along the lightning channel. Atmospheric conditions such as temperature and humidity affect the sound of thunder and how far it can be heard.