On Tue, 18 Jan 2005 21:41:16 +0100, "md" not given to avoid spam wrote:

I think Mach 1 is defined as the sound of speed at sea level at 0 deg C. Implicitly we mean "on
earth".
Mach 1 is therefore an absolute number, and the same everywhere in the universe.

That would not be a useful definition. The Mach number is defined as the ratio
of actual speed to the speed of sound in a given medium. In the case of aircraft
on Earth, the actual speed of Mach 1 is a function primarily of altitude. Any
article on Titan that uses Mach 1 as a synonym for the speed of sound at sea
level on the Earth is clearly using the term incorrectly.

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Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com