NavList:

George wrote:
"If the time was known, there would be no point in taking a lunar. That's
the purpose of measuring a lunar-distance; to determine the time. So
there's a bit of a paradox, in calculating altitudes with which to clear a
lunar, for which time and position are both needed. To get round it, you
have to assume a trial longitude first, and then use the lunar observation
to refine that assumption".
--------

Exactly so. George has expanded on my terse meaning. He has said more accurately what I meant.

I too have noted mention of using calculated altitudes to obtain time from a lunar distance if the altitudes were not obtained accurately (perhaps due to a hazy horizon?) and I wondered how they were to do that without a chronometer, when the whole purpose was to find time (and hence longitude) in the first place.

It became apparent when it is suggested recalculating the altitudes with the found approximate calculated time, and then recalculating the lunar distance to give a new more accurate time - in other words an iteration process.

The question is: does this converge? and how quickly. To save my going in to the maths to find out - does anyone know?

Douglas Denny.
Chichester. England.
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