NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Iterative Lunar method
From: Fred Hebard
Date: 2019 Feb 20, 09:07 -0500
From: Fred Hebard
Date: 2019 Feb 20, 09:07 -0500
You shoot the altitudes of the objects in a lunar in order to obtain their refraction correction, for which you don’t need accurate altitudes The refraction correction is small and doesn’t change much, less than 4’ at 15 degrees altitude, and less than 1’ at 45 degrees. Tables of refraction, such as http://www.siranah.de/manuals/Table_Refraction.pdf, are enumerated in whole degrees. So if you can get your altitude sight to within 1 degree of arc, you’re fine. In contrast, airmen and small boat sailers try to get shots to within a minute of arc and mariners to within a few tenths of a minute.
I hope Frank will give us a more elegant, quantitative answer to this question.
On Feb 20, 2019, at 08:01, Frank Reed <NoReply_FrankReed@fer3.com> wrote:In any case, you can find out how a single observer would do the work in most old manuals of navigation. You shoot the altitudes before the lunar distance sights, then shoot them again after. It takes only simple averaging to synchronize them with the distance observations.
Many modern navigators, accustomed to the frantic timing of observations of celestial altitudes, make the incorrect assumption that the altitudes must be measured with great accuracy and careful timing, but that's all wrong.
