Why lightning reaches your eyes before thunder reaches your ears
Lightning produces a flash and rapidly heats air, creating the pressure disturbance heard as thunder. Light travels vastly faster than sound, so the flash reaches you first. In air near room temperature, sound covers roughly one kilometre in three seconds, making the delay longer for more distant lightning.
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Two signals with very different speeds
A lightning discharge heats the surrounding air rapidly. The resulting rapid expansion creates a pressure wave that travels outward and is heard as thunder.
The light from the discharge arrives far sooner because light travels vastly faster than sound. Over everyday distances, most of the noticeable delay is the sound's travel time.
At about room temperature, sound travels through air at roughly 343 metres per second. That corresponds to approximately one kilometre in three seconds.
- A longer delay generally indicates a more distant discharge.
- Air temperature changes the speed of sound.
- A long lightning channel can produce an extended rumble rather than one sharp clap.
The timing is an approximate distance illustration, not a precise location measurement or a reliable way to decide whether a storm is safe.