A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2016 Oct 14, 15:23 -0700
I know of no other program that even attempts to reproduce the Nautical Almanac values for the hourly GHA of the Sun.
"Astro-Nav" does just that. The author states that:
Part of the comprehensive coverage of AstroNav is its ability to produce conventional Nautical Almanac pages for any year. [...] Less than 0.5% of entries will differ from printed tables. The vast majority are due to rounding or truncation at extreme levels. When high precision sources were used to check differences during program testing, half agreed with AstroNav.
Attached is an example output for the next three days corresponding to pages 202-3 of the current Nautical Almanac. The only difference in the GHA of the Sun I spotted was on the 15th at 0700. AstroNav gives a GHA of 288°34.3', whereas the Almanac gives 288°34.4'. (I haven't bothered to check other pages.) However, the program comes with its own set of "increments and corrections" tables which seem to differ more often with the NA. So, one would still get a different result from the NA more often when interpolating using only the AstroNav materials.