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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Datum for Nautical Almanac
From: Michael Dorl
Date: 2004 Oct 29, 10:32 -0500
From: Michael Dorl
Date: 2004 Oct 29, 10:32 -0500
In reply to my msg, George Huxtable ; wrote: >The ellipsoidal shape of the Earth is allowed for already in our charts. >Instead of taking the Earth as a sphere, in which case all the lines of >latitude would be equally spaced, they are redefined as lines where the >direction of gravity makes an equal angle with the Earth's axis. This >"fiddle" allows to forget about the Earth's ellipsoidal shape, though it >complicates any exact calculation of the distance from A to B on the >Earth's surface. I understand that declination is independent of the reference spheroid provided the spin axes agree. are the following statements concerning the NA true? Decl and GHA/SHA are with respect to earth's mean equator and equinox. Diurnal; aberrations effects are not included. Diurnal parallax effects are included based a spherical earth of (I don't know radius). The suppositions concerning diurnal effects are made since the NA contains no corrections based on position; the NA corrections depend only on observed altitude.