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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: No sextant, no watch, no almanach, nothing
From: Trevor Kenchington
Date: 2004 Nov 5, 23:56 -0400
From: Trevor Kenchington
Date: 2004 Nov 5, 23:56 -0400
Alex, Geoffrey's method would need a star catalogue but not necessarily an almanac. Since the stars are fixed (at the level of precision of instrument-free navigation), the declinations of the brighter ones can be learnt with relatively little difficulty. (Equivalent knowledge, though not expressed as "declinations", formed a key component of traditional Polynesian navigation. It didn't need the support of astronomers, telescopes and printed tables of numbers.) Determination of the zenith without a sextant is said to be possible by lying on deck, sighting up the mast, and visually averaging the position of the masthead against the sky. However, I think I would rather memorize the stars with declinations equal to my chosen co-latitude. When on the intended parallel, those stars should of course be just circumpolar, grazing the horizon at each inferior meridian passage -- something that could be observed with reasonable precision at tropical and temperate latitudes. Or you can make a kemal suited to the latitude you are planning to sail down, particularly if it is in the northern hemisphere and Polaris is available. Trevor Kenchington You wrote: > Dear Geoffrey, > I am not sure that I really understand the details of the method you > describe but it seems to be based on the almanac. > The people you mention just used the almanac BEFORE > their trip to select the stars. > > In principle, you can memorize some data from the almanac, > then leave the almanac at home and use the data from your > memory:-) > > For example, the hero of Mark Twain novel "Yankee at the court of > king Arthur" memorized the day and time of a solar eclipse:-) > > (He just happened to read an almanac before his travel.) > I would not call this "navigation without almanac". > > Second, how do you detect without a sextant when a star it in zenith? > I don't think this is easy to do. > > Alex. -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus