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On Jun 4, 2005, at 3:41 AM, 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.
>

George,

As you know, a meridian passage shot can give a very accurate latitude,
as the only datum needed is the maximum altitude of the body.  GMT or
local time need not be known.  Peter Fogg pointed out some of the
difficulties when the Sun is near zenith, but most places and times in
the world, it works fairly well

Without knowing GMT, one could not determine longitude from an altitude
of the Sun when it is due East or West.  I also wonder how much the
altitude of the sun varies with azimuth at various locations when it is
due East or West; it's azimuth can only be measured to perhaps 0.1
degrees, how much would that limit the precision of the measurement?  I
don't know enough about math and the sight-reduction equation to
estimate this, other than by brute force calculation for various
locations.

Fred

   

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