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    Re: The Nautical Day
    From: Herbert Prinz
    Date: 2004 Feb 7, 17:01 -0500

    George Huxtable asked:
    > It opens up another question, however.
    > Assume that mariners were indeed universally accustomed to using the
    > nautical day in their logs. Considering that the new Nautical Almanac had
    > been especially prepared for their use, and indeed the Greenwich
    > Observatory had been set up primarily for the benefit of nautical
    > astronomy: then why were the astronomers so bloody-minded as to use the
    > astronomical day, rather than the nautical day, for the Nautical Almanac
    > tabulations? Conservatism, presumably. "That's the way we astronomers have
    > always done it."
    You are providing us with a reductio ad absurdum of your second premise.
    The correct name of the publication in question is "Nautical Almanac and
    Astronomical Ephemeris for the Year ...". In the preface we read "A work which
    must greatly contribute to the Improvement of Astronomy, Geography, and
    Navigation." (In this order!) This introductory sentence which describes the
    general purpose of the Almanac gets easily lost in the excitement about lunar
    distances in the several subsequent paragraphs.
    The French emphasize their focus already in the title of their ephemeris, which
    originally read: "La connoissance des temps", but soon had the addition "[...],
    a l'usage des astronomes et des navigateurs". Again, the astronomers come
    Both publications (but the Connoissance a little more so) contain information
    that was exclusively designed for use on land, such as the Jupiter satellite
    eclipses, a map of the features of the Moon, aspects of planets, or the
    Equation de l' Horloge. There is something for everybody: Land exploration,
    surveying, pure astronomy (selenography), civil administration. And if I am not
    mistaken, I even smell an astrologer hiding behind a corner.
    Would not, for example, the tabulation of Jupiter satellites in nautical time
    have been paradoxical? And the use of yet another time scale within one and the
    same almanac rather awkward?
    As to the purpose of the Greenwich Observatory: Sure it was set up for the
    particular benefit of nautical astronomy, but astronomy is furthered by
    astronomers, not seamen. Astronomers need ephemerides to improve their theory.
    Before the almanacs came into existence, frequently required information was
    spread out over different publications of varying accessibility, standards and
    ease of use.
    Herbert Prinz

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