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    Re: NOW what?
    From: Bob Goethe
    Date: 2015 Aug 15, 09:03 -0700

    >>This  article is very confusing: the prime meridian cannot be wrong.
    The prime meridian is arbitrary....
    Where you decide to draw it there it will be.<<

    One key phrase in the article is that the position of 0.0° was subject to "the imposed condition of continuity in astronomical time (between various observatories)". 

    Time is defined by clocks in various locations (hence the "C" of UTC), after corrections have been introduced to account for variations in local gravity.  These corrections must be applied to make astronomical observations of, for instance, a given quasar consistent with observations of that same quasar at other observatories.  If you define "directly overhead" by your observations of a bowl of mercury, your astronomical results are going to be slightly inconsistent with those of other observatories, which each have their own unique versions of "overhead" defined by their own bowls of mercury.

    And as it turns out, Greenwich Observatory has its OWN variation as well.  And it became just one among many observatories in terms of defining time.

    Your notion of where the center of mass is for the earth is going to cause you, once you mix it in with your idea of what time it is, to to have a particular understanding of where meridians of longitude should be located.  GPS satellites use just such an understanding of the earth.

    Time and longitude are, as I have come to understand from dialogs in this group, basically interchangeable when it comes to navigation.   If you give others the right to define the correct time, then your right to define your own longitude is going to be slightly limited.

    Bob

       
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