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Andres provided a plot of sextant altitude against time, and wrote-

"The average in this case is incorrect, see the Hs graph:"

He doesn't say which average is wrong, the average altitude or the average
time. I have checked and rechecked my result, given as -

"Averaging the 8 observations, I get the mean altitude of 72� 26.0', at a
mean time of 21h 01m 57s. Hope others agree." I can find nothing wrong with
that averaged altitude, to the nearest 0.1', which would correspond to
72.433� on Andres' graph, and wouldn't appear to be at all out of place as
an average within the points he has plotted.

The averaged time is a bit different. On second thoughts, I now make the
averaged time to be 21h 01m 47s, 10 seconds earlier than the figure I gave,
which was no doubt the result of my careless arithmetic, first time round.
Sorry about that. Was that the incorrect average that Andres refers to?

However, it makes no difference whatever to the result. That 10 second error
doesn't change the Moon's dec (not when working to the nearest 0.1',
anyway), but it will shift the Moon's GHA, by 2.5'. As I had written, "In
this exercise, the geometry is such that only the dec matters, not the GHA."
So the result is unaltered. Nevertheless, it shows what care is called for
in the arithmetic.

 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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