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In earlier postings, I had expressed several doubts about a passage, in a
mailing from Frank (5239), in which he said-

"By the way, if you want to think about lunar distance observations
differently, each lunar generates a line of position, which you could plot
on a chart just like any other LOP. But unlike standard altitude LOPs, an
error of 0.1 minutes of arc in a lunar distance observation implies a 6 n.m.
error in the lunar LOP. One advantage is that you can shoot lunars when the
horizon is hidden. Cross two lunar LOPs and you get a rough position fix. "

And now, in 5255, he has clarified the matter.

And as a resut, the penny has dropped! I can now understand what that
passage was all about.

This time, he really DID have me completely confused, so I am pleased that
he has cleared the matter up.

His reference to a "lunar" or a "lunar distance" was not to using those
terms as we would normally understand them, to get time. Instead, they were
observations made at a precisely known GMT, then their use by working
"backwards" to deduce a position, however imprecisely, from the Moon's
parallax I don't complain of the use of those terms in that context (they
did indeed relate to measurement of a lunar distance) but the words called
for some explanation or qualification, for "the rest of us". Perhaps the
phrase "think about using lunar distance observations differently" was
intended to provide a clue.

Anyway, he completely fooled me. I had no notion that he was bringing his
old hobby-horse out of its stable for another parade.

Yes, it's an amusing notion that could work, at least in theory, were it not
so limited by its impracticality. Frank only manages to achieve some sort of
respectabilty by basing its error on an observational precision of 0.1', the
same as he claims for his own sextant observations: a precision unmatched,
as far as I know, by any other observer ever.

George.

contact George Huxtable at george@huxtable.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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