Judging the distance of lighting

  • 5 seconds = 1 mile
  • 10 seconds= 2 miles
  • 15 seconds = 3 miles
  • 20 seconds = 4 miles

You can rarely hear thunder that originated more than 20 miles away, because the sound waves get scattered and absorbed by the atmosphere over time and distance. Why does thunder from a single flash sometimes last for a few seconds even though the flash seems instantaneous? It's because you are hearing a series of thunder "bits" from various parts of the lightning flash. Since the bolt may be sharply forked, the sound from different sections can hit your ear at different times as it radiates outward.

The other way to listen to lightning is on your AM radio. Every flash makes light waves and radio waves -- two different forms of electromagnetic energy. Just as our eyes sense light waves, AM radios sense waves in the AM spectrum and amplify them so we can hear them through the radio. You can tune into AM lightning by finding a station on the AM dial (the lower frequencies are best). Listen for pops of static -- each one is from a lightning flash. Unlike thunder, which travels at the speed of sound, AM radio signals travel at the speed of light, which is a million times faster -- 186,000 miles per second. So you can see a lightning bolt and hear its pop on the radio at the same time, even if the thunder itself takes a few seconds to arrive.