The big bang in the sky.
Mach was named after the 19th century Austrian physicist Ernst Waldfried Mach, who was also a teacher of Einstein. The so-called Mach number refers to the ratio of the speed of an object to the speed of sound in the medium through which it is moving.
As a young physicist, Mach was intrigued by the study of shock waves and enlisted the newly available technology of Schlieren photography to capture the shadows of otherwise invisible shock waves created by bullets. A visual image of the compressed air that a bullet would produce when travelling faster than sound allowed Mach to measure and describe the phenomenon and ultimately formulate his theory of supersonic speed. The Mach number was first used in the 1930s. And an aircraft flew faster than Mach 1.0 only in 1947. Now the record speed for an aircraft with a pilot is 6.7 times the speed of sound.
