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    Re: Compass correction using sunrise
    From: David Pike
    Date: 2022 Jun 27, 14:38 -0700

    Francois.
    You were looking for lost minutes of time of sunrise.

    I think I spot two problems.
    1. If you start with sunrise is 03.50 local time (which I confirmed in the Air Almanac) at 62
    ° 28’W, you need to add (62x60 + 28)/60x15 = 3748/900 = 4.164 hrs = 4hrs 10 minutes, not 4hrs, to get sunrise at Greenwich i.e 08.00UTC, not 0750UTC

    2. From 07.50 to 08.13 is 23 minutes of time.
    Interpolating directly, Sunrise at 48
    ° 17.5’N should be 1° 42.5’/5° x23 minutes of time after sunrise at 50N.  I.e., or 102.5'/300' x 23 = 8minutes of time after sunrise at 50N, not 18 minutes as you’ve calculated.  Overall sunrise at your position should be 08.00UTC + 8 minutes = 08.08UTC. which is a bit closer to Al’s value.
    Without knowing more about Al’s spreadsheet and almanac sunrise time, I can’t explain the remaining missing 6 minutes.   DaveP

       
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