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    Re: suggestion for a satisfactory celnav narrative
    From: Joel Jacobs
    Date: 2005 Jun 4, 13:50 +0000
    A couple of additional comments that Peter stimulated..
     
    When near the equator as he said, the likely hood of the sun crossing your meridain overhead is pronounced. The answer to having your head back is to precalculate its altitude. The azimuth will change very rapidly as it crosses your Lon, but the altitude will not and you will have time to fine tune it.
     
    IMO, the other reason LAN sights are so popular is because you do not need tables to solve for Lat.
     
    Joel Jacobs
     
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    -------------- Original message from Peter Fogg <fthre{at}OPTUSNET.COM.AU>: --------------


    > George Huxtable wrote-
    >
    > > To answer Bill's question, if a time-sight is taken at the moment when the
    > > Sun is due East or due West of the observer, then his latitude isn't
    > > needed at all in calculating local time-by-the-Sun. But that can only
    > > happen in the Summer months.
    >
    > This is true, although what George hasn't added, perhaps considering it
    > assumed knowledge: The resulting position line (LOP) is the longitude.
    > As George has noted, it can be married with a noon sight (if moving; via a
    > running fix) to give an elegant 2 body fix, of a line of latitude and
    > longitude each. The accuracy is dependent (apart from the usual issues) on
    > how well the movement between the! two sights can be plotted (run forward).
    >
    > > To my mind, finding latitude at noon is a trivial matter that presents a
    > > problem only when the sky is cloudy at noon.
    >
    > Well, its not trivial in latitudes where the sun approaches the zenith. It
    > tends to be more difficult generally to make observations of bodies near the
    > zenith. Its about the only time when having a good idea of the azimuth by
    > observation (a corrected compass reading) is problematical. Plus the sun in
    > full tropical mode plus the awkward contortions of trying to take a sight of
    > the blazing sun with the head tilted back at 90 degrees to the body, the eye
    > sockets filling with sweat - mean that noon sights in such places may be
    > notable by their absence.
    >
    > > >Perhaps the fact that "longitude by noon sun" comes up so often
    > > >is a good reason that there *should* be a discu! ssion of this
    > > >method, pointing out why it is a bad idea...
    >
    > Nah, its all grist to the mill. There's nothing good or bad, as Shakespeare
    > said, only thinking makes it so ... If it serves a useful function (at least
    > when it comes to nav) then its all good. Not perfect, mind. Good is simply
    > good.
       
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