NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A triangle on the equator
From: Lars Bergman
Date: 2025 Oct 20, 08:36 -0700
From: Lars Bergman
Date: 2025 Oct 20, 08:36 -0700
Kermit, you wrote "Anybody to comment here on the actual spherical radius to be used ?"
There are at least three sphere radii to choose among:
Taking the mean value of the ellipsoid's three semi axes, Rm = (a+a+b)/3 = 6 371 008.8 m
Taking a sphere with the same surface area as the ellipsoid, RA = a·(1 - e2/6 -17/360·e4 - ...) = 6 371 007.2 m
Taking a sphere with the same volume as the ellipsoid, RV = a·(1 - e2)1/6 = 6 371 000.8 m
Using sphere radius = 6 371.0 km fits all three!
Lars
