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Determination of Longitude or an LOP by sunrise/sunset observations was
and is an accepted navigational method and is covered in many older
texts, as well as in those dealing with lifeboat navigation. In solution,
a negative altitude is employed which may not be compatible with short
tabular methods, but works perfectly well with a time sight solution. I
suppose some argument can be advanced with respect to uncertainties of
refraction, but the method is otherwise entirely useable.
On Thu, 22 Jul 2004 09:46:43 -0500 Jim Theriot <> writes:
> Bill said:
>
> > The idea struck me that at sunrise and sunset I could get a LOP
> without a
> > sextant. One barrel of my binoculars, a heavy-duty
> neutral-density
> filter,
> > a watch, Nautical Almanac and HO229 tables would suffice.
>
> I was struck by a possibly similar idea -- I am not sure if it's the
> same
> idea,
> because Bill's comments are mostly about use of almanac and tables,
> not
> about
> the basic principle. My idea was simply that for any observation
> you make
> with watch and sextant where the object appears on the horizon, the
> same
> observation could be made with watch only (or watch and binoculars).
> Then
> you run the computations, using using zero for the sextant reading,
> making
> all
> the appropriate corrections (but using zero for the sextant index
> error
> correction!), and you should get identical results. Possibly that's
> what
> Bill was getting at.
>
> Furthermore, it seems that on a moonless night you might be able to
> get
> a LOP from the setting of a star or planet more easily using this
> method,
> since you don't have to see the horizon, you only need to note the
> instant
> at which the star or planet blinks out.
>
> I wanted to test this theory on a sailing trip a couple of months
> ago (I
> live inland, not in sight of a 'real' horizon), but weather and
> circumstances
> prevented it.
>
> Regards,
> Jim
>
