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    Re: Unexpected USNO height correction precepts
    From: Paul Hirose
    Date: 2018 Sep 19, 00:28 -0700

    On 2018-09-17 10:45, Antoine Couëtte wrote:
    > Would you agree that the USNO precepts could be better fine-tuned ? or do 
    you think that this topic is only about "splitting hair" ? Nonetheless - and 
    if I am not mistaken in my enclosed computations - we are encountering a case 
    here where the intercept derived from the USNO precepts and recommendations 
    seems to be in error by 0.7 NM which could otherwise have been avoided.
    
    Unfortunately, Antoine's attachment contains his phase corrections but
    says nothing about the basis for computing them. I don't know the
    formulas. In my Lunar4 program you can select lower limb, upper limb, or
    body center, but not center of light.
    
    The Almanac says "the phase correction for Venus has been incorporated
    in the tabulations for GHA and Dec, and no correction for phase is
    required." It is curious that such corrections are not included in the
    USNO Web calculator
    
    http://aa.usno.navy.mil/data/docs/celnavtable.php
    
    A note near the bottom of that page says, "The data for Venus has not
    been corrected for phase; under certain conditions this could displace
    the center of light up to 0.3 arcminutes." But Antoine says his example
    has .7' error if phase is ignored.
    
    Since we're talking about tenths of minutes, I think Antoine's example
    should be worked both ways at .01' precision to (practically) eliminate
    roundoff errors from the comparison.
    

       
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