As an airplane flies faster than the speed of sound, it "pushes" on the sound
waves in front of it. But sound waves obey the speed limit—they can't travel
faster than the speed of sound. So the waves pile up against each other as they
are created. These "piled up" waves are called shock waves. The greatest shock
waves are at the tip and tail of the plane. This NASA photograph shows the
shock waves created by a plane in flight (The "rings" in the photograph are
camera artifacts and are not part of the shock waves; for more information see NASA:
Schlieren
Photography - Ground to Air)