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    Re: Nautical Almanac
    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 " 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 " .


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