NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Latitude by Lunar Distance
From: Wolfgang K�berer
Date: 2006 Nov 10, 01:31 -0800
From: Wolfgang K�berer
Date: 2006 Nov 10, 01:31 -0800
Dear all, while looking for more information on George's problem of when the drum sextant was introduced, I stumbled over an article outlining the procedure that Frank invented. It is: J�ger, M. Eine astronomische Ortsbestimmung ohne Kimm oder Libelle durch Ermittlung der H�henparallaxe des Mondes. in: Annalen der Hydrographie und Maritimen Meteorologie, Jg. 40 (1912), 541 - 544. So the idea is not exactly original or new (94 years) and has been published in a peer-reviewed journal before, I am sorry to say. Regards, Wolfgang Alexandre E Eremenko schrieb: > This method is essentially based on the Moon parallax. > (Imagine that the Earth is very small. Then the > method will not work: all lunar distances are > the same, independently of your place on a small Earth). > > To estimate the accuracy, notice that the ratio > of the distance to the Moon to the Earth radius is > 60 (very roughly). So the loss of precision due to the > method is by the factor of 60 under the most > favorable conditions. > These most favorable conditions are: > a) The Moon is near zenith, and > b) The two directions Moon-star are perpendicular. > > So under these conditions, the method is less accurate > than the usual Lunar distances by a factor of 2. > If the Moon's altitude is 30, > multiply by enother factor of 2. > > Now it is hard for me to believe that one can > measure distances with 0.1 or even 0.2 accuracy > permanently and reliably:-) > Some results posted by Frank seem to show that he can, > but it is still unclear whether he posts his best > results of average results:-) > > I still have no definite opinion on this matter, > but my analysis of observations of Cook's expedition > seems to indicate much lower accuracy than 0.2' > And this was done from the ground, > by professional astronomers, possibly with the best > sextants ever made (?) > > The Lunar method was advertized as having approx 1/4 of > a degree accuracy. This I believe. > Then the lunar-with-chronometer-but-no-horizon > method has probably 1/2 degree accuracy or so. > > Alex. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---