NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Nautical Almanac
From: Stan K
Date: 2016 Jul 19, 13:07 -0400
From: Stan K
Date: 2016 Jul 19, 13:07 -0400
Kermit,
Ah, the memories! Gary opened that can of worms back in January of 2011. Of all the suggestions, I like using a smaller font and squeezing the v value for 1200 UT of the middle day of the page at the bottom of the Sun column, along with the SD and d.
In my Celestial Tools program, which is primarily intended as an aid to students taking the Power Squadrons Junior Navigation and Navigation courses, I have two "modes" for the hourly GHA of the Sun. In the "Accurate val. of hourly GHA" mode, the values will agree with most computer-generated almanacs. In the "NA val. of hourly GHA" mode (the default), the program tries to reproduce the values found in The Nautical Almanac. I say "tries" because it is not perfect. It only works for about 99% of the 8760 hours in a (non-leap) year, and when it doesn't agree, it is only off by 0.1'. (With the help of a friend, all 8760 hours of 2014 were tested.) In a way this 1% difference is fortunate, as the mandate for Celestial Tools was that it help students find errors in their work, not do the work for the student. This 1% requires that students consult The Nautical Almanac.
Stan
-----Original Message-----
From: Antoine Couëtte <NoReply_Couette@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Tue, Jul 19, 2016 10:29 am
Subject: [NavList] Re: Nautical Almanac
From: Antoine Couëtte <NoReply_Couette@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Tue, Jul 19, 2016 10:29 am
Subject: [NavList] Re: Nautical Almanac
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 " https://thenauticalalmanac.com/2016%20Nautical%20Almanac.pdf " than from The 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 " https://thenauticalalmanac.com/2016%20Nautical%20Almanac.pdf " .
Kermit
