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    Re: Semi-diameter of moon
    From: Frank Reed
    Date: 2018 Jan 20, 12:52 -0800

    Yes. That's right. The total correction table UL/LL for the Moon in the back of the Nautical Almanac incorporates parallax, refraction, semi-diameter, and augmentation of semi-diameter. It's all in there. The SD is directly proportional to the HP at any instant. In fact, the Moon's HP is essentially identical to the SD of the Earth as seen from the Moon! So if we flip the viewpoint, the SD of the Moon is necessarily equal to the Moon's HP multiplied by the ratio of the Moon's diameter to the Earth's diameter which is taken as 0.2724 in our navigation tables:
       SD = 0.2724 · HP.

    Incidentally, I agree completely with Gary LaPook that the standard correction table for the Moon in the Nautical Almanac is more trouble than it's worth. It's one of those cases where the designers way back in the 1950s were being clever -- too clever! It would be better pedagogically and possibly in other ways to have seeparate tables for the individual components of the correction for the Moon.

    Frank Reed

       
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