NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2021 Oct 29, 12:11 -0700
Frank,
In further reference to my earlier post to which you just replied here, - thanks for your quite detailed reply - let's again take a look at the the USNO Web Application clone following results:
Celestial Navigation Data for 2021 Oct 19 at 21:59:27 UT
For Assumed Position: Latitude N 41 18.4
Longitude W 72 30.0
Almanac Data | Altitude Corrections
Object GHA Dec Hc Zn | Refr SD PA Sum
o ' o ' o ' o | ' ' ' '
SUN 153 39.1 S10 18.4 - 0 15.2 256.4 | -31.0 16.1 0.1 -14.8
MOON 339 48.3 N 4 02.6 + 0 38.9 85.2 | -24.0 15.0 55.2 46.2
VENUS 106 55.5 S25 40.0 +15 49.0 212.0 | -3.4 0.0 0.2 -3.2
JUPITER 33 22.6 S15 08.8 +22 57.4 138.6 | -2.3 0.0 0.0 -2.3
SATURN 48 53.7 S19 19.7 +25 32.1 155.2 | -2.0 0.0 0.0 -2.0
ARIES 358 27.2
Moon phase is waxing, 99% illuminated.there is a definite refraction correction error for the Moon which should show -31.0' exactly like for the Sun, instead of currently showing -24.0' .
As earlier surmised, the Moon refraction Correction showing up as " -24.0 " is the Inverse Refraction - actually the right refraction function to be used in such reverse engineering - applied by error to the Geocentric Height "Hc" while it should be applied to the Topocentric unrefracted height.
BODY | Hc | Inverse refraction from Éphémérides Nautiques | Published Refr in |
SUN | -0°15.2’ | -30.04’ | -31.0’ |
MOON | +0°38.9’ | -24.03’ | -24.0’ |
VENUS | +15°49.0’ | -3.37’ | -3.4’ |
JUPITER | +22°57.4’ | -2.27’ | -2.3’ |
SATURN | +25°32.1’ | -2.01’ | -2.0’ |
As earlier surmised, this mismatch is only visible onto Low Alt Bodies with a significant HP, in other words, it is only visible for Lady Moon quite close from the Horizon.
Hence it fully explains why the example you just published shows a perfect match between the former USNO Web Application and the current USNO Web Application clone since Lady Moon height is about 25° in it.
This bug should be very simple and straightforward to correct : simply apply Inv (Ref) to Topocentric Height vs. Geocentric height.
Hope it helps !
Antoine M. "Kermit" Couëtte
antoine.m.couette[at]club-internet.fr
