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    Re: CN on Mars
    From: Frank Reed
    Date: 2016 Feb 6, 15:29 -0800

    Stan, you wrote:
    "Wouldn't it still be 30 Martian nautical miles?"

    Ha! I knew you would get in on that one. :)

    This comes down to how you want to see things: Is a nautical mile a fluid definition that varies with the size of the body on which we perform our measurements with the only rule being that there are 5400 of them from equator to pole? That is, should a minute of arc in latitude always equal a nautical mile? Or is a nautical mile a measurement that has become fixed by modern (re-)definition which means that it's a certain number of meters, ad if you go to another planet a nautical mile "out there" is still a "terrestrial" nautical mile?

    You might think that this hasn't been decided yet, but we do, in fact, have a solid historical precedent in favor of the latter. Communications between NASA mission control and the Apollo astronauts in lunar orbit routinely quoted altitudes in nautical miles above the lunar surface, and those were terrestrial nautical miles. No chance they would have used a fluid definition allowing lunar nautical miles. So I'm afraid, Stan, that you have the full weight of NASA and Apollo against those localized nautical miles! There will be no martian nautical mile.

    Frank Reed
    PS: Speaking of the Apollo astronauts, as of Thursday, there are now seven out of twelve who walked on the Moon still alive. The remaining seven are all over 80 years old. 

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