A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Lars Bergman
Date: 2018 Nov 8, 02:13 -0800
"You calculate the lunar distances for the time period in question or use a table of pre-calculated values."
The problem is that the geocentric rate of change that you get from calculated lunar distances is generally not equal to the observed (i.e. measured by sextant) rate of change. This topic was discussed some fifteen years ago in this forum, I think it was this phenomena that was called "parallactic retardation". Is there any simple method to find the expected rate of change of your observed distances, without using the observed data?
The geocentric rate of change is (was) easily found through the proportional logarithm shown alongside the lunar distance in the Nautical Almanac. But how translate that to the slope of my sextant readings?