Thunder is made by lightning superheating the air so fast that it explodes outward, creating a powerful shockwave that your ears hear as a rumble or crack.

What thunder actually is

Thunder is just sound.

It comes from the air around a lightning bolt being heated to tens of thousands of degrees Celsius in a tiny fraction of a second, hotter than the surface of the Sun.

Step‑by‑step: how thunder is made

  1. Lightning forms in a storm cloud (usually a tall cumulonimbus cloud).
  1. The lightning current races through the air, heating a narrow channel of air extremely quickly.
  1. That air expands explosively, pushing on the surrounding cooler air and creating a shockwave, like a tiny explosion.
  1. The shockwave turns into sound waves that spread out in all directions; this is the thunder you hear.
  1. As the heated air cools and contracts, the vibrations continue along the lightning path, giving thunder its long rumbling sound.

Why thunder sometimes cracks and sometimes rumbles

  • A sharp crack usually means the lightning strike was close, so you hear only a small part of the path clearly.
  • A long rumble happens when the lightning is far away or very long, so you hear sound from different parts of the bolt arriving at slightly different times.

Why you see lightning before you hear thunder

  • Light travels much faster than sound, so the flash reaches your eyes almost instantly.
  • Sound travels much slower through air, so the thunder arrives later; counting the seconds between flash and rumble gives a rough idea of how far away the storm is.

Information gathered from public forums or data available on the internet and portrayed here.