NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant Positions versus Map Datums?
From: Rodney Myrvaagnes
Date: 2002 Jan 17, 9:48 PM
From: Rodney Myrvaagnes
Date: 2002 Jan 17, 9:48 PM
On Thu, 17 Jan 2002 13:22:32 -0800, Hal Mueller wrote: > >Sextant positions are referenced to the surface of this ellipsoid, >not to a sphere. Sextant positions measure from gravity vertical, to the extent they measure from anything. That is inherent in a water surface. To the extent that gravity remains normal to the astronomers' ellipsoid, your statement makes sense. However, even assuming that perfection, how would anyone using a sextant distinguish that vertical from the vertical of a sphere? An observatory can establish its celestial coordinates with a lot of measurements over time. A sextant doesn't have that luxury. And, gravity has lots of local variation. How does the WGS84 ellipsoid compare with the astronomers one? Rodney Myrvaagnes J36 Gjo/a "Religious wisdom is to wisdom as military music is to music." "What contemptible scoundrel stole the cork from my lunch?" -- W. C Fields
