What is thunder?
Quick answer from Eartha
Thunder is the sound made by lightning. Lightning is so hot that it heats the air around it faster than you can blink, making the air suddenly expand and shake. That shaking sends out a booming sound wave, and that boom is thunder. Light travels faster than sound, so you always see lightning first.
The longer story
During a storm, lightning is an enormous spark of electricity zapping through the sky. It's incredibly hot, reaching temperatures hotter than the surface of the sun for a tiny moment.
That heat makes the air around the lightning bolt expand super fast, almost like a small explosion. This sudden movement of air creates powerful sound waves that ripple out in every direction.
Those sound waves are what we hear as thunder, a deep rumble or a sharp crack depending on how far away the storm is. Nearby lightning sounds sharp, while far-away lightning sounds like a long rumble.
You almost always see the lightning flash before you hear the thunder boom, even though they happen at exactly the same moment. That's because light zooms to your eyes almost instantly, while sound travels much more slowly, taking about three seconds to travel one kilometre.
Try this at home: count the storm's distance
- Next time you see lightning from a safe spot indoors, start counting seconds until you hear thunder.
- Divide the number of seconds by three to guess how many kilometres away the storm is.
- Watch the next flash and see if the storm is getting closer or further away.
Words to know
- lightning
- A giant, fast spark of electricity in the sky during a storm.
- sound wave
- An invisible ripple of moving air that carries sound to our ears.
- expand
- To suddenly get bigger or take up more space.
For grown-ups: what is my child learning here?
Age band: Ages 5-8
Curriculum link: Australian Curriculum v9 Science, Year 1 to Year 3, Earth and Space Sciences strand: observing and describing weather events.
The concept: The child is learning that thunder and lightning happen together and that light and sound travel at different speeds.
More classroom ideas are on our teachers page, and safety notes for families are on for parents.
Last reviewed: · How we check answers
More questions kids ask
Got a nature question of your own?
Ask Eartha your own question →