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George knows enough about this, but for some others a word of caution. Make sure sure you are dealing with two azimuths that are NOT nearly the reciprocal of one another, so that the LOPs would always be obtuse angles and not result in nearly parallel LOPs. If you had too much of a time interval bewteen sights, the two lines crossing would be acute angles and the point of Lon would be a matter of judgement where the lines crossed with little mathematical precison.
Joel Jacobs
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-------------- Original message from George Huxtable <>: --------------
> Bill Noyce wrote-
>
> >Perhaps the fact that "longitude by noon sun" comes up so often
> >is a good reason that there *should* be a discussion of this
> >method, pointing out why it is a bad idea...
> >
> >Is there any other observation that gives longitude without
> >knowing latitude first? Maybe this is part of its appeal.
>
> ================
>
> To my mind, finding latitude at noon is a trivial matter that presents a
> problem only when the sky is cloudy at noon.
>
> 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.
>
> But why, in this age, does a mariner still ask for separate determinations
> of latitude and longitude? It's as if we were still stuck in the early
> 1800s, and Sumner and St Hilaire had never invented position lines. Why not
> just measure two altitudes of the Sun, at any old times, but times which
> are well separated so that the Sun's azimuth has changed significantly
> between them. Then draw a couple of position lines from some assumed
> position, allow for vessel's run in the interval, see where they cross, and
> that's where you are, in lat and long. Simple as that. Applies to any sight
> of any body at any time: a universal way of doing the job. Who needs
> anything different?
>
> George.
>
> ================================================================
> contact George Huxtable by email at , by phone at
> 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
> Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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