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Bruce Stark said-

>We finally had some clear weather, which I used to get a measurement of
>Parallactic Retardation. George's phenomenon cut the moon's apparent motion
>to about three quarters of her geocentric motion.
>
>Over a period of a little over an hour I took three sets, five contacts each,
>of the moon's near limb and Pollux. The moon was so high I had to lie on my
>back, and was within two degrees of the meridian for the last set. By then it
>was late, so I called it quits. The first set missed GMT by 54 seconds. The
>second missed by 14 seconds. The third missed by 49 seconds. All three slow.
>
>If anyone would like to look at the sextant readings and watch times I'll
>post them. Just bear in mind that I have to look through a four power scope
>with trifocals, and have the beginnings of cataracts.
>
>By the way, I like the name "Parallactic Retardation." It's the phenomenon
>itself that I don't like.
>
>Bruce

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Comment from George-

I for one would be most interested to see the details of Bruce's
observations. It's gratifying that they confirm the evil effects of
parallactic retardation. Together with Bruce, it's something I deplore, but
it's a fact-of-lunars and we just have to make the best of it. The great
surprise to me is that such a major effect hasn't been picked up in the
standard textbookss (not the ones I've read).

I expect that the figures would also be instructive to others such as
Arthur Pearson, who are just starting to pick up the skills of the lunar
trade, to show what can be achieved, even with imperfect eyesight.

Presumably Bruce's lunars obtained Sun and Moon altitudes by calculation
from the Almanac, knowing in advance what the GMT was going to be. I would
like to take his same observations but recalculate them with a different
time base , say half-an-hour ahead of GMT, as if he was using a deck watch
that was half-an-hour fast for all his observations. And then see how close
to GMT the first-iteration comes. And perhaps the second iteration. And so
on. It is much more satisfying to make such a test with real observations
rather than with invented data.

George Huxtable.

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george@huxtable.u-net.com
George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
Tel. 01865 820222 or (int.) +44 1865 820222.
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