NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2025 Mar 1, 05:12 -0800
Robert VanderPol II, you asked:
"Would adjusting the PM sight up or down by distance traveled (nm) N or S be an acceptable alternative methodology?"
Yes, absolutely. The tabular correction works well, and it's quicker. But simple addition of altitude offsets works well, too. One detail here: you said "the PM sight" as if you're considering only one. That's not terrible, but this process is significantly more effective if you have a half-dozen or a dozen sights centered on local apparent noon. That improves the accuracy considerably.
You mentioned Hewitt Schlereth's book devoted to this topic, and I do recommend it, but it's getting hard to find. The same process is discussed in the Admiralty Manual of Navigation from a theoretical point of view, and we can certainly re-derive it. Anyone interested in working through that? There's a relatively simple equation involving tan(Dec) and tan(Lat) that will tell us how many seconds we need to add or subtract to adjust for the large impact of observer motion on a longitude derived from a near-noon Sun curve.
Frank Reed
