A sonic boom is the explosive thunderclap sound that happens when something travels faster than the speed of sound. Sound moves through air at about 767 miles per hour at sea level (called Mach 1), and when a jet fighter or spacecraft pushes past that speed, it creates a powerful shock wave that people on the ground hear as a loud BOOM.

Here's what happens: as any object moves through air, it pushes air molecules out of the way, creating pressure waves that spread out in all directions. Normally these waves move ahead of the object as regular sound. But when something accelerates past the speed of sound (going supersonic), it's moving so fast that it catches up to its own sound waves and compresses them into an intense wall of pressure. When that compressed wall of air reaches your ears, you hear the boom.

The Concorde, a supersonic passenger jet that flew from 1976 to 2003, created sonic booms so loud that it was banned from flying at supersonic speeds over land in most countries. Military jets still create them during training, and people on the ground could hear them when the Space Shuttle used to return to Earth. The boom doesn't just happen once when the aircraft “breaks the sound barrier.” Instead, the aircraft drags that shock wave behind it like an invisible cone the entire time it flies faster than sound, and anyone underneath the flight path hears a boom as the cone sweeps over them.