NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Unexpected USNO height correction precepts
From: Paul Hirose
Date: 2018 Sep 19, 00:28 -0700
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.
