Mach number temperature generally decreases with increasing altitude between sea level and , the speed of sound also decreases. For example, the standard atmosphere model lapses temperature to at altitude, with a corresponding speed of sound (Mach1) of , 86.7% of the sea level value. While the terms "subsonic" and "supersonic", in the purest sense, refer to speeds below and above the local speed of sound respectively, aerodynamicists often use the same terms to talk about particular ranges of Mach values. This occurs because of the presence of a "transonic regime" around M = 1 where approximations of the Navier-Stokes equations used
Mach 1: A Story of Planet Ionus Mach 1: A Story of Planet Ionus Mach 1: A Story of Planet Ionus is a 1957 science fiction novel by Allen A. Adler. A paperback version was published in 1966 by Paperback Library with the alternate title Terror on Planet Ionus. While testing an experimental warship, the "Mach 1", a human pilot and his companion are kidnapped into space by aliens from the planet Ionus, which turns out to be a moon of Saturn. There, they confront an oversized monster named Karkong who is menacing the Ionians. Karkong follows them back to Earth. Chaos ensues. Damon Knight wrote of