A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Jim Rives
Date: 2020 Nov 23, 06:01 -0800
I have been doing lunars pretty regularly since the beginning of the year. Normally I take the opportunity to determine my Index Error using the Sun-on-Sun method, as it seems to be more reliable than the split horizon method. I had expected to be able to confirm my calculation of IE by comparing the resulting calculated Semi-diameter (SD) with the SD published in the Nautical Almanac. However, I noticed right away that it was off... so initially I thought it was some sort of rounding error. However, the data for the past six sights shows a calculated SD that is consistently .2 minutes smaller than the published SD. The IE determined averages +2.6 pretty consistently. I had thought that I should be able to come to the published SD normally. Can anyone make any suggestions as to what could be causing this. Should I be able to agree to the SD per the Nautical Almanac?