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This is enough to make my head spin!

Now that it's phrased this way, parallactic retardation _seems_ to be
an effect that could affect accuracy: if the apparent lunar distance
were not changing at all for some period, then clearly the times at the
beginning and end of that period could not be differentiated based upon
the apparent distance, which would be the same.  The cleared distances
would be different, but not the apparent ones.  We know the moon
doesn't appear to stand still, but this degradation of accuracy would
persist to a lesser extent if it were appearing to move more slowly,
would it not?

One point that came to mind, which George addressed off list, is that
if the rate of change of the apparent distance is being retarded below
average at some point, it must be accelerated above average at another
to maintain the average.  That acceleration occurs while the moon is on
the other side of the earth, which prevents one from observing it then
(I believe we can all agree on this last point)!

On Jan 15, 2004, at 12:14 PM, George Huxtable wrote:

> To get to the real lunar distance you MUST measure the apparent lunar
> distance (whether it's changing with time or not), and then apply a
> correction which, being precisely known, does not degrade the accuracy
> of
> that measurement. Because the resulting true Moon is always moving
> about
> the same speed across the sky, it can always be used to measure time
> with
> about the same accuracy.

   

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