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Douglas Denny wrote-"No need for retractions I think."

No, I thought that might be too much to expect.

"If stationary - as I was with my observations (and which you ignored) -
then culmination of the apparent (true) Sun is by definition Local Apparent
Time of the (true) Sun."

Perhaps "culmination" was an unfortunate word for us to be using between us,
because it can be ambiguous.
The Oxford English Dictionary states- "Of a heavenly body: To reach its
greatest altitude, to be on the meridian.", as though these two events
coincided. But for the Sun, they differ, even for a stationary observer.
That is the very nub of our discussion. So let's avoid "culmination".

If we rephrased Douglas' statement, above, to read-
"Local Apparent Time is, by definition, 12 hours at the instant when the
true Sun crosses the observer's meridian", then I suggest both of us might
accept those words

But that is not the instant of greatest altitude of the Sun; not even for a
stationary observer, because of the Sun's changing declination. The
difference may never be much more than a quarter of a minute of time, but it
isn't zero (except at the solstices).

(For the Moon, because its declination changes much faster, the time
difference between meridian passage and maximum altitude can amount to many
minutes.)

In many situations, such as deciding on the best moment to observe for a
noon Sun latitude, that time difference can indeed be ignored, for an
observer who is stationary or slow-moving. But when the longitude is to be
derived from timing the Sun's changing altitude, it must be considered;
otherwise, it will just add a systematic error to the result, which varies
with time-of-year. That's what Douglas has neglected to take into account.
If he is simply claiming that such a correction is too small for him to
bother with, in view of the limited precision of the observation, then that
would be fair enough. However, he appears to be denying the case for such a
correction at all, as I read his postings. Is that his position?

Douglas added-"This is all treated with rigor in Charles H. Cotter's book
'The Complete Nautical Astronomer' with full formulae for calculation of
these effects and full derivations."

Thanks for bringing that Cotter book to my attention. I hadn't come across
it before. Cotter also treats these questions in his "History of Nautical
Astronomy", (1968), but some aspects are confused, and several of his
equations are wrong. Perhaps he had got things clearer by 1969.

=============================

I ask again: what happened to the claim, in [9932], that-

"The difference is 0.000737068 degrees,  or 0.04422408 minutes,  or 2,6
seconds of arc.

Utterly  negligable "

Does Douglas wish to defend that claim, or perhaps withdraw it? What does it
mean?

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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