Distance of Lighting Strike

A thunderstorm is approaching, and suddenly you hear an absolutely deafening clap of thunder. At times it becomes frightening! But how close is the lightning, really?

It is difficult to determine the distance of a lightning bolt just by looking at it, and the volume of the thunder isn’t a good way to tell either. Here's a potentially life-saving method you can use to approximate how far away lightning is.

Approximation

If we consider the atmosphere on a standard day at sea level, the speed of sound is about 330~340 m/s. Light travels in vacuum and space at approximately 299 792 458 m/s. We can use this knowledge to approximately determine how far away a lightning strike has occurred.

• Watch the sky for a flash of lightning.
• Count the number of seconds until you hear thunder.
• Divide the number of seconds by 3 (distance in kilometers).

We see the flash immediately as it happens. The speed of sound is more or less 1km per 3 seconds. If the thunder can be heard after T seconds, we can approximate the lightning strike was D ≈ T/3

Dependence on weather conditions

The speed of sound is variable and depends on the properties of the substance through of which the wave is traveling.

Sound travels through air at slightly different speeds depending on air temperature, relative humidity, altitude, pressure, wind conditions, etc. However, the difference is fairly small and won’t substantially affect your calculations.

Points to note:

• The speed of sound in dry air at 0 degrees C is about 330 m/s
• Water vapor in the air increases this speed slightly.
• Sound travels faster through warm air than through cold air.