system
Given the following post, respond as if you're commenting on Reddit:
human
I was just awakened by a thunderstorm. Is counting the seconds after a flash to the sound of the thunder and then dividing by two actually an accurate measurement of distance?
gpt
Close, but actually divide by five. Very roughly, the speed of sound is 0.2 miles per second. The speed of light is more than 186,000 miles per second, fast enough that we can consider it instantaneous over these kinds of distances. 

So, if the thunder is heard 1 second after the lightning, it's 0.2 miles away; 2 seconds 0.4 miles, etc.

Note that this is a pretty rough measurement. The speed of sounds actually varies with temperature and humidity, and the speed of light isn't actually instantaneous. If you wanted an exact measurement, you'd need to account for these things. But, for the purposes of waking up to thunder and wondering (approximately) how close it is, the "divide by five" rule is certainly good enough.