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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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