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    Re: Eclipses and longitude
    From: Frank Reed
    Date: 2026 Aug 24, 14:51 -0700

    Lyle Ruppert,

    I admit I have done no more than skim your post, but I want to hit one key detail right now while I have a few minutes to spare.

    You mentioned a "parallax correction". I may not have read closely enough, but if you mean the parallax of the Moon, the nice thing about a lunar eclipse is that the local "topocentric" or ground-based parallax of the Moon doesn not matter in an eclipse. The Earth's shadow is "painted" on the Moon, striking certain craters and mountain features at the same moment of absolute time as seen by all observer on the Earth (excluding those for whom the Moon is invisible, below the horizon or hidden by weather). This is radically unlike lunar distance observations, for which the parallax is critical for each observer. We don't have to worry about parallax at all in lunar eclipses.

    Think of a lunar eclipse like an explosion going off on the Moon. Everyone who can see the 'big bang' at all, sees it happen simultaneously in terms of absolute time. Or imagine someone with a big powerful laser point drawing a little sign on the Moon that says "now!" for one second at some pre-determined UT. :)

    Frank Reed

       
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