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    Re: Longitude at noon
    From: Philippe Posth
    Date: 2020 Sep 9, 11:56 -0700

    Hi Tracy,

    Thanks for your example, it will help me explain what I am trying to say.

    The culmination time you have determined is 19h23min37s UT on September 7, 2020.

    The "normal" calculation I've seen everywhere is:

    On that day, the Greenwich Passage Time was 11h57min51s

    The difference between the 2 times is 7h25min46s.

    By multiplying this time by 15 we get your longitude: 111°26.5'W

    The "second" calculation is:

    GHA at 19h: 105°33.9'; Increment for 23min37s : 5°54.3'

    GHA at 19h23min37s = Longitude = 111°28.2'W

    Which calculation is correct? Why this (small) difference?

    Thank you all (from France)

       
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