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    Re: AM and PM time sights
    From: Lars Bergman
    Date: 2021 Nov 10, 04:04 -0800

    Herman,

    If you define easterly longitude as positive, then
    LHA = GHA + Long, from which
    Long = LHA - GHA

    In the formula you use, cos(LHA) = C = A - B, you have to be aware of the fact that cos(LHA) = cos(-LHA). So when you calculate LHA = arccos(C), LHA can have any sign. As the example you show is an AM Sun sight, then we know that 180° < LHA < 360°. So your LHA is (using integer values for clarity) -52°, or -52° + 360° = 308°. Thus your longitude
    Long = LHA - GHA = 308° - 134° = 174°. As the result is positive the longitude is east.

    You can as well use LHA = -52°, then
    Long = LHA - GHA = -52° - 134° = -186°. As the result is negative the longitude is west. But 186°W equals 174°E.

    Lars

       
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