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    Re: Captain Cook & celestial navigation
    From: Wolfgang Köberer
    Date: 2020 Feb 5, 02:04 -0800

    Geoffrey is right, of course. The article must be read as referring to an observation at Greenwich.

    Apart from that the thing is simple, but readers - and writers - are probably confused when thinking of Greenwich as a place and not thinking of Greenwich time.

    The tabulated lunar distances in the NA are geocentric distances which means they apply to any place on earth not only to Greenwich– otherwise one could not use them everywhere. Therefore they don’t reflect observations at Greenwich. Greenwich is only used as a time reference because the geocentric distances must refer to a definite time (not a place). The reference time could be the time of any place – Paris or Berlin for instance for the Conaissance des temps or the Astronomisches Jahrbuch. Greenwich time is used in the NA as that then facilitates the calculation of longitude measured from the prime meridian which is in Greenwich (and was used by British navigators who used the NA even before the prime meridian conference in 1884).

    Regards Wofgang

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