A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2016 Jul 19, 05:19 -0700
Hello to all !
Well ... if you directly interpolate the Sun GHA from its published hourly values instead of getting it through our usual Sun GHA Interpolation Table based on a 15° hourly rate, you will get slightly better results from an [uncorrected] Almanac like " " than from The Almanac.nauticalalmanac 2016 Nautical Almanac
Single Table full accuracy Sun GHA interpolation cannot be implemented since the Sun Hourly GHA oscillates yearly with +/- 0.3' from its 15°/hour average value. To best interpolate it with one corrective term only, it would have implied some 5 different Sun Correction Tables: hence our classical "pseudo correction" reaching up to 0.2' in the published values in The Almanac to minimize the unescapable built-in method inaccuracy when using one single Sun GHA Interpolation Table.
An alternate solution - but a less convenient one for other reasons - would have been to publish a SUN GHA interpolation table based on its slowest hourly change (close to 14°59'7) while daily publishing a second positive corrective term ranging from 0.0' to +0.5'. This method has been retained for Lady Moon where such daily second correction term is much more important.
But again - and as long as we accept to use a calculator - since we now have all computational [calculator(s)] power to perform accurate linear interpolation, better use "true" - i.e. unbiased [apparent] - GHA data such as the ones published in Almanacs like " nauticalalmanac 2016 Nautical Almanac " .