Lightning flashes before thunder because light moves faster than sound
In short: Lightning and thunder are caused by the same storm, but light travels faster than sound, so we see the flash before hearing the rumble. Learn how to estimate distance using the time gap and why thunder is a warning sign.
Lightning is a sudden electrical discharge that heats the air around it to temperatures hotter than the surface of the sun. This rapid heating causes the air to expand violently, creating a shockwave that we hear as thunder. Because light travels at about 300,000 kilometers per second and sound travels at roughly 343 meters per second, we see lightning almost instantly but hear thunder several seconds later.
To estimate the distance of a lightning strike, count the seconds between the flash and the thunder. Divide that number by 3 to get the distance in kilometers. For example, if you count 15 seconds, the lightning is approximately 5 kilometers away. However, this is an estimate, and if you hear thunder, you should seek shelter immediately.
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Sources
- Summary by Intellect · source: Why Do We See Lightning Before Hearing Thunder? ⚡
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