What Causes the ‘Sound’ of Thunder and Why Does It Vary?

Thunder is the sound of lightning. When lightning hits, it makes a big boom. But sometimes thunder sounds like a whisper or a loud roar, that depends on where you are and how far away the lightning is.

If you're close to the lightning, you hear a big boom right away. If you're farther away, the sound takes longer to reach you, so it might be more of a low rumble or even a soft whisper.