Have you ever seen lightning without hearing the accompanying thunder ? This type of silent flash is often incorrectly called a “ heat flash ”. What is it really ? This is a flash exactly the same as the others, neither more nor less.
A flash seen at a great distance
“Heat lightning” is actually produced by distant thunderstorms so far away that you can see the lightning which is signaled by brief flashes streaking across the sky but the thunder can’t be heard from where you are because of the distance.
Here’s why: the speed of light (about 300,000 km/s or 186,282 miles per second) is extremely fast compared to that of sound (300 m/s – 1,086.9 feet). In addition, the thunderclap and its wave dissipate more easily by propagating and, when one is too far away, the thunder is no longer heard and becomes inaudible.
If during a hike you are caught in a thunderstorm, remember that the shorter the time between the lightning and the thunder, the closer you are to the impact of the lightning and the more danger you are in. To calculate the distance between you and lightning, count the number of seconds that separate the sight of lightning from the sound of thunder. The shorter this time, the faster you have to take shelter !
