July 1, 2004

Q: What causes thunder?

A: Thunder is caused by lightning. The bright light of the lightning bolt represents a great deal of energy. This energy heats the air to above 50,000 degrees F in only a few millionths of a second. The superheated air has no time to expand, so it starts out at a very high pressure. The high pressure air then expands outward into the surrounding air compressing it and causing a disturbance that propagates in all directions away from the lightning bolt. The disturbance is a shock wave for the first 10 yards, after which it becomes an ordinary sound wave, or thunder.