Lightning always happens first, followed by thunder. The reason we see the lightning before we hear the thunder is that light travels much faster than sound. Light travels at around 300,000,000 meters per second, while sound moves at 340 meters per second. When lightning strikes, it heats the air around it to at least 50,000 degrees Fahrenheit, causing the air to expand explosively. This rapid expansion and contraction create the sound wave that we hear as thunder. The sound of thunder can only be heard for a distance of about 10 miles from the lightning strike. The time between seeing the lightning and hearing the thunder can be used to estimate the distance between you and the lightning strike. If you count the number of seconds between the flash and the thunder and divide by five, you can calculate the distance in miles.