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I think what you are trying to say, George, is that during a lunar sight two 
parallax compensations must be made, not one. The first is the constantly 
changing parallax caused by the terrestial observer rotating [sic] under the 
moon. The second being the constantly changing parallax between the moving 
moon and the celestial background.

So there is no singular "parallax" involved with lunars, but rather, two sets 
of parallax corrections. One caused by the inconvenient terrestial observer, 
who cannot maintain a constant position with regard to the moon, and the 
second caused by the moon, which is orbiting both the sun and the earth, with 
a resulting motion that I'm not sure how to describe, except perhaps by 
saying that the moon "corkscrews about" in space, relative to the celestial 
background.

Without seeing the changing motions diagrammed on a board I'm not at all sure 
how serious the errors they cause will be, or ot what extent they can be 
ignored, much less how they can be compensated for. Since it was only some 35 
years ago that "we" as a planet did not even have sufficient computational 
power to accurately describe the exact path for the lunar missions, I don't 
feel bad at not being able to precisely understand the effects of two 
separate parallax adjustments being involved in lunar distance calculations. 
(As you may recall, a midcourse correction was planned for and performed, 
because the orbital mechanics and thrust controls could not be made 
accurately without stopping to make corrections en route.)

So, a change in the change? No. Two sets of parallax corrections, and the 
dynamics between them and the overall observation, yes. That's much clearer 
to me, if that's what it is.

   

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