NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: parallax of the sun
From: Frank Reed CT
Date: 2004 Sep 20, 21:46 EDT
From: Frank Reed CT
Date: 2004 Sep 20, 21:46 EDT
Fred H wrote:
" It's usually 0.1' of arc. Is it tabulated or mentioned in the Nautical Almanac? I couldn't find any mention of an actual value."
That's close enough. The parallax of the Sun is 9 seconds of arc at the maximum level of accuracy required for any lunar distance sights. This varies during the year but only by +/-1.6% so the change in parallax is negligible from the perspective of lunars. Note that the Sun's semidiameter also changes during the year and that's why there are two columns for the Sun's altitude correction in the Nautical Almanac (1.6% *is* significant for the SD, insignificant for the parallax itself). You can get the Sun's center altitude correction including refraction and parallax by taking the appropriate UL and LL values from the Nautical Almanac and averaging them.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
" It's usually 0.1' of arc. Is it tabulated or mentioned in the Nautical Almanac? I couldn't find any mention of an actual value."
That's close enough. The parallax of the Sun is 9 seconds of arc at the maximum level of accuracy required for any lunar distance sights. This varies during the year but only by +/-1.6% so the change in parallax is negligible from the perspective of lunars. Note that the Sun's semidiameter also changes during the year and that's why there are two columns for the Sun's altitude correction in the Nautical Almanac (1.6% *is* significant for the SD, insignificant for the parallax itself). You can get the Sun's center altitude correction including refraction and parallax by taking the appropriate UL and LL values from the Nautical Almanac and averaging them.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
