An Etymological Dictionary of Astronomy and Astrophysics

Half of the vertex angle of the → Mach cone
generated by a body in → supersonic flight.
It is given by sin μ = (a/v), where a is the speed of the sound waves and v the velocity of the object. In terms of Mach number: μ = asin (1/M). The Mach angle diminishes with the object velocity. For M = 1 it is 90°, for M = 2, it is 30°, and for M = 5, its is 11.5°.

See also: → Mach number; → angle.