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    Re: Lunar Distance in Wikipedia
    From: George Huxtable
    Date: 2007 Jul 25, 15:22 +0100

    Frank referred to-
    
    "this odd idea of the "Sun at
    | its zenith" when trying to say that it has reached its maximum
    | altitude. No one trying to communicate navigational or astronomical
    | concepts should use zenith that way. The zenith is straight up. That's
    | all.
    
    ==========================
    
    Response from George.
    
    Well, as one notorious for his own pedantry, I am agog. If Frank claims to
    be able to hold his finger in the dyke, against the tide of change, he will
    be sadly disappointed. Neologisms abound, even in the technical literature;
    indeed, especially in the technical literature. There are no rules. Words
    mean what people understand them to mean, writing them and reading them.
    
    Certainly, when unqualified, "the zenith" refers to the observer's zenith;
    straight up, and nothing else. What makes such a usage as "the Sun at its
    zenith" acceptable, if undesirable, is this. It's quite clear that it isn't
    referring to the "observer's zenith". Instead, it's a zenith belonging to
    the Sun, because it says so. And there can be little doubt that what's being
    referred to is the highest point in the Sun's path, so there's no chance of
    confusion. Is there an alternative single word available to say the same
    thing? "Culmination", perhaps, but to how many people would that have a
    meaning?
    
    But here a bit more pedantry is called for. Neither the Sun's "zenith", nor
    its culmination, nor its highest point in the sky, is the real moment of
    apparent noon. Local apparent noon is when the Sun crosses the observer's
    meridian, so to us in the North, it's exactly South of us. And because the
    Sun's declination is continually changing (at around 1 knot at the
    equinoxes, but not at the solstices) the Sun's altitude is changing
    slightly, even as it crosses the meridian.
    
    For example, at the latitude of Greenwich, around the Autumn equinox, the
    Sun's highest moment occurs something like 40 or 50 seconds before, at noon,
    it crosses the meridian. In spring, it's the other way. These are
    non-negligible time errors that have to be allowed for, in many
    applications.
    
    George.
    
    contact George Huxtable at george---.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
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