A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2016 Oct 16, 13:24 -0700
As usual, we’ve kind of galloped away on this.
The thing is, have we answered Axcel’s original questions?
By way of a start, NA Item 24: ACCURACY Main Data really needs to be read in conjunction with NA Item 6 second paragraph:
Anyway, so what is the conclusion of all this? Is it that the v-correction is already built into the hourly tabulated GHA values? All right then, but if this was advantageous, why is this not done for all the planets but only the Sun? I also still have a problem to see why the resulting error due to the manipulation of the tabulated GHA values is so small. If you look in September and take a full hour value of the Sun and interpolate it for 60 minutes (i.e. you add 15° to it) and compare it with the tabulated value of the following hour you will get a difference of 0.3' So which is the more accurate value now? According to the email of the UKHO the interpolated value - do I understand that correctly?
This whole thing remains a mystery to me. I could imgaine that this whole effort of integrating the v-correction into the tabulated GHA is for the sake of converting longitude into time. Could that be the case? For this longitude into time calculation to be accurate, we actually need to divide the distance (longitude or GHA) by the actual speed of the Sun, which obviously is not constant. The solution by the Nautical Almanac is to keep the speed constant but to adjust the distance (GHA) so that the end result is fairly close to the proper calculation. Does that make sense...?