Sketchplanations
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Flash-to-bang method

Two hikers look at distant lightning and count how long it takes to hear the thunder to estimate how far the lightning is away

How far away is the storm? The flash-to-bang method can help.

When lightning is made by a storm the rapid heating and expansion of the air create the thunderclap. But because sound travels slower than light, there's a gap between seeing the lightning and hearing the thunder it produced. Using Distance = speed x time, by counting the seconds from seeing the lightning you can easily estimate how far away it is.

Conveniently, the speed of sound in air is about 330 metres/second. So depending on your unit preference:

  • every 3s you wait the thunder travels about 1 km
  • every 5s you wait the thunder travels about 1 mile

Give it a try at a safe distance from your next lightning storm.

Also see: thunderclap or rumble, thunder clouds, dirty thunderstorm

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