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    Re: Longitude at noon
    From: Tracy Shrier
    Date: 2020 Sep 9, 14:58 -0700

    Hi Philippe,

    Are you are missing the difference between Mean sloar time and Apparent solar time? I know UT in the Air Almanac is Mean time. I recorded LAN with my watch referencing UT. Staying in the Almanac to reduce Long from GHA obviates the need for reconciling the difference. Does calculating Long from the time difference between Greenwich noon and LAN require the additional correction of the Sun's analemma - the 'equation of time'? Those on the NavList that know so much more can weigh in for us.

    Also of interest to me is the different GHA you derived: 111°28.2' vs my 111°27.9'. Not a big difference but is yours from the Nautical Almanac?   

    Lastly, in reviewing my work I see that I recorded the Sun's dec wrong, correctly using d = 5°40.2' gives me Lat 40°46.0' N, 0.6' off my GPS in my back yard!

    Tracy

       
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