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As I reported to the list earlier, my observation
of the small Lunar distance when the Moon was close to Jupiter
was successfull, except the unexpected large change in the Index error.
At noon before the observation I checked it with Sun, it was -0'4,
and the check seemed very reliable (small scattering, and 4SD matched).

Then I took the Lunar in extreme cold, the temperature dropped from
about 40F at noon (in fact I observed at noon from my room,
so the sextant was under the room temperature) to 8F at the time of Lunar
observation, (the sextant was brought outside 1/2 before the observation)
the first measured distance was terrible (almost 2' error with -0'4 IC) so
I rechecked
the IC from stars and found -1'2 (also very consistently, 5 or 6 different
star observations). After that the Lunar was OK, not only the short
one but also a long one.

Next day I checked again with Sun in the morning. The temperature was
20F, and I cooled the sextant for 1 hour outside before the observation.
The index error was -0.5.

If this is really temperature dependent fluctuation, is not it
too large for a high quality metal sextant ?

Alex.

   

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