Many have probably heard the term “heat lightning” tossed around from time to time throughout the summer. The typical theory is that hot and humid conditions produce lightning, even without rain or thunder, causing the night sky to light up..
While this theory is commonplace, it is completely false, and there is really no such thing as “heat lightning." the truth behind this myth is that we are actually seeing flashes of light reflecting off of clouds from lightning in a distant thunderstorm. Just how far away? Far enough that you cannot hear thunder. This is because sound waves disspate as they travel through the atmosphere. The exact distance thunder can travel is tough to pinpoint as temperature can affect how far it can be heard. For example, sound waves move slower and travel less distance in cooler, denser air, and propagate faster in warmer air. But in general, if you are more than 10 - 15 miles away from a bolt of lightning, you probably won't hear the thunder. However, the light from the strike can be seen up to 100 miles from the parent thunderstorm! Pretty amazing stuff.
