The sonic boom is produced when a shock wave emanating from an aircraft in supersonic flight reaches an observer. Such waves are generated in the discontinuities of the device, such as the wings, although they normally join to form two: one from the nose and another from the queue. As they leave the apparatus, the two waves gradually separate due to a small difference in the angle between them. When they reach an observer on the earth's surface, this divergence can be significant, and if the interval of passage of the two waves is greater than 0.1 seconds , two separate booms will be heard. If the time lapse is shorter, the human ear cannot differentiate the two waves and hears only one.
The space shuttle penetrates the atmosphere at supersonic speeds, causing two shock waves, one at the nose and one at the tail. As their length is 37 meters, the waves are separated by an interval of about 0.11 seconds. When they reach the ground, the small difference in the angle between them increases such distance, so that an observer who listens to the passage of both waves will do so with a delay of 0.11 seconds and will be able to distinguish two booms.
