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    Lunar distance presetting exercise
    From: Peter Hakel
    Date: 2019 May 26, 09:30 -0700

    About an hour ago I conducted a quick exercise presetting a sextant to the Sun-Moon near-limb distance (no refraction corrections).
    Sextant: Astra III Professional with the 7x35 Celestaire telescope
    Calculations with Navigation Spreadsheets (screenshots attached)

    Date: May 26, 2019
    Local time: 9:25 am, U.S. Mountain Daylight Time
    Universal Time: 15:25
    Location: 35° 53’ N, 106° 19’ W

    Sun:
    GHA: 51° 59.4’
    Dec: N 21° 08.8’
    SD: 15.8’

    Moon:
    GHA: 137° 19.1’
    Dec: S 13° 17.7’
    SD: 14.8’
    HP: 54.3’

    Topocentric lunar distance: 91° 07.0’
    Subtracting the sum of the two semidiameters: 30.6’
    Presetting the sextant to: 90° 36.4’

    Then, I pointed the sextant at the Moon and soon the Sun appeared right on top of Moon’s limb, as expected. I did not even check the index error beforehand (the sextant has been sitting in its box for months). The whole procedure lasted less than 15 minutes; doing this write-up took somewhat longer than that. :-)  A good result overall.


    Peter Hakel
    https://www.navigation-spreadsheets.com

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