We’ve all heard it.
That loud, sometimes house-rattling boom during a thunderstorm.
Sometimes it startles us out of our sleep.
But what is causing that loud, explosive sound?
The short answer is, lightning. While it may seem as though lightning and thunder are happening at the same time in a nearby thunderstorm, it is actually the lightning that comes first.
Lightning strikes are very hot, and can heat up the air to around 50,000 degrees Fahrenheit! That’s 100 times hotter than a typical wood fire! When you heat up the air, it expands, and in this case very rapidly, creating that loud clap of thunder.
You may have heard that you can tell how far away a thunderstorm is by counting the seconds that pass between seeing the flash of lightning and hearing the thunder. Divide that number by 5 and you can tell how many miles away the lightning struck. The reason this works is because light travels much faster than sound.
When a thunderstorm is directly overhead, you see lightning at the same time you hear thunder. The farther away from the storm you move, the longer it will take for the sound of the thunder to reach your ears after you see the lightning.
While loud thunder can sound scary, thunder alone is not dangerous, but the lightning that causes it is. If you can hear thunder, you are close enough to lightning that it is not safe to be outside. That’s why you should always remember: when thunder roars, go indoors.