Why Do We See Lightning Before Hearing Thunder?
Have you ever watched a storm and noticed something strange?
A flash of lightning appears in the sky—and only a few seconds later comes the loud crash of thunder.
But lightning and thunder are produced at almost the same time. So why the delay?
The answer is simple: light travels much faster than sound.
Light travels at about 300,000 kilometres per second, while sound travels through air at only about 343 metres per second.
So when lightning strikes several kilometres away, its light reaches our eyes almost instantly. The sound takes much longer to reach our ears.
In fact, we can use the delay to estimate how far away the lightning is.
Roughly, every three seconds between the flash and the thunder represents about one kilometre of distance.
So the next time you see lightning, count:
One... two... three...
If the thunder follows after about six seconds, the storm is roughly two kilometres away.
A storm has therefore given us a simple natural clock:
The flash tells us when it happened.
The thunder tells us how far away it happened.
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