NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Longitude via lunar altitudes, simplified
From: Frank Reed CT
Date: 2007 Feb 7, 00:32 EST
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From: Frank Reed CT
Date: 2007 Feb 7, 00:32 EST
Longitude by lunar altitudes was invented and debated at least 250 years
ago. It has been rediscovered many, many times since then and dismissed again
and again, too. There was an article in MNRAS by a Lieutenant Ashe of the Royal
Navy in 1849 describing his pleasure in discovering this method and noting that
it might be more practical than longitude by lunar distances. The article is
interesting primarily not for his calculational method, which looks like
the long way around to me, but for his introductory comments and the editor's
notes at the end. In the intro, Ashe mentions that he has seen the chronometers
checked by lunar distances only once in his twenty years of experience at sea,
which is good evidence on the era when they had fallen out of use. Like far too
many commentators, Ashe assumes that this was because lunar distance
calculations were too difficult (this was definitely not the case). At the end
of the article, the "editor" (possibly G. B. Airy himself) notes that the
problem with longitude by lunar altitudes is intrinsic: the horizon can't be
trusted and the Moon's motion along its orbit is inclined relative to the
horizon. I don't feel I have the time to keyboard this, but the comments
are relevant, so I'm going to cheat and attach the text as an image file.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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