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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction, sunset, and HO229 beginner question
From: Henry Halboth
Date: 2004 Jul 25, 15:30 -0400
From: Henry Halboth
Date: 2004 Jul 25, 15:30 -0400
Determination of Longitude or an LOP by sunrise/sunset observations was and is an accepted navigational method and is covered in many older texts, as well as in those dealing with lifeboat navigation. In solution, a negative altitude is employed which may not be compatible with short tabular methods, but works perfectly well with a time sight solution. I suppose some argument can be advanced with respect to uncertainties of refraction, but the method is otherwise entirely useable. On Thu, 22 Jul 2004 09:46:43 -0500 Jim Theriotwrites: > Bill said: > > > The idea struck me that at sunrise and sunset I could get a LOP > without a > > sextant. One barrel of my binoculars, a heavy-duty > neutral-density > filter, > > a watch, Nautical Almanac and HO229 tables would suffice. > > I was struck by a possibly similar idea -- I am not sure if it's the > same > idea, > because Bill's comments are mostly about use of almanac and tables, > not > about > the basic principle. My idea was simply that for any observation > you make > with watch and sextant where the object appears on the horizon, the > same > observation could be made with watch only (or watch and binoculars). > Then > you run the computations, using using zero for the sextant reading, > making > all > the appropriate corrections (but using zero for the sextant index > error > correction!), and you should get identical results. Possibly that's > what > Bill was getting at. > > Furthermore, it seems that on a moonless night you might be able to > get > a LOP from the setting of a star or planet more easily using this > method, > since you don't have to see the horizon, you only need to note the > instant > at which the star or planet blinks out. > > I wanted to test this theory on a sailing trip a couple of months > ago (I > live inland, not in sight of a 'real' horizon), but weather and > circumstances > prevented it. > > Regards, > Jim >