Ever seen a fighter jet rush past you so fast that you hear a loud bang? Well, that loud bang is called a sonic boom. Now, what exactly is a sonic boom? A sonic boom is a thunder-like noise a person on the ground hears that is associated with shock waves created when an object travels through the air faster than the speed of sound, or “supersonic.” The boom is not a temporary sound that is heard when an object flies by but rather it is a continuous effect that occurs while the object is traveling at supersonic speeds. It mainly affects only observers that are positioned at a point that intersects a region in the shape of a geometrical cone behind the object. This effect to the root level is called the “Doppler Effect”.

Cause

Air reacts like a fluid to supersonic objects. As those objects travel through the air, molecules are pushed aside with great force and this forms a shock wave. The bigger and heavier the aircraft, the more air it displaces. When an aircraft passes through the air, it creates a series of waves in front of the aircraft and behind it. These waves travel at the speed of sound and, as the speed of the object increases, the waves are compressed, because they cannot get out of each other’s way quickly enough. Eventually, they merge into a single shock wave, which travels at the speed of sound, a critical speed known as Mach 1 which is is approximately 1,235 km/h (767 mph) at sea level and 20 °C (68 °F). To simply put, the shockwave is produced when the pressure front moves at supersonic speeds and pushes on the surrounding air.

NASA makes history

NASA captured one of the best photographs in recent aviation history where they successfully tested an advanced air-to-air photographic technology in flight, capturing the first-ever images of the interaction of shockwaves from two supersonic aircraft in flight. The image helps to aid in the study of how shockwaves interact with each other. It features a pair of T-38s, flying in formation at supersonic speeds. The T-38s are flying approximately 30 feet away from each other, with the trailing aircraft flying about 10 feet lower than the leading T-38. With exceptional clarity, the flow of the shock waves from both aircraft is seen, and for the first time, the interaction of the shocks can be seen in flight. To capture these images, a Beechcraft King Air aircraft was used which was flying a pattern around 30,000 feet and had to arrive in a precise position as the pair of T-38s passed at supersonic speeds approximately 2,000 feet below. Meanwhile, the cameras, able to record for a total of three seconds, had to begin recording at the exact moment the supersonic T-38s came into frame.

Sources:

• https://www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html
• https://en.wikipedia.org/wiki/Sonic_boom
• https://theconversation.com/fastn-loud-how-to-create-sonic-booms-and-curious-clouds-54190 (Cover photo)