NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Andrew Bauer
Date: 2022 Oct 22, 08:35 -0700
Part 2:
Disappointed with the Plate Carrée projection to depict Lunar Distance charts, I turned to a stereographic projection, in particular an equatorial stereographic projection as the Moon travels more or less along the ecliptic path and should be positioned roughly centrally.
A stereographic projection has the advantage of being conformal. Unlike the Constellation Maps in Wikipedia that use a Polar stereographic projection where all lines of longitude are straight lines and all lines of latitude are circular, in an equatorial stereographic projection both longitude and latitude lines are circular (and cross at right angles) with one exception: the Equator and the Central Meridian are straight lines.
Local scale is preserved in every direction, i.e., small circles on a sphere appear as circles (not ellipses) on a plane. However, scale increases moderately with increasing distance from the center (origin) and a consequence of this is that it is only practical to map up to about 75% of the sphere’s surface. 50% is a hemisphere or 180° of longitude. I chose to map 190° of longitude to get that extra reach without making the map too wide.
LD charts in stereographic projection may be downloaded from:
https://thenauticalalmanac.com/
I include here the LD charts for November 2022. These may be compared with the Plate Carrée projections in my previous post. I would be pleased if my contribution finds a couple of smiles amongst other readers!