NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lindy Line
From: George Huxtable
Date: 2002 Dec 5, 23:41 +0000
From: George Huxtable
Date: 2002 Dec 5, 23:41 +0000
Response from George- Aren't we doing well! Five heads are better than one. I now agree with what Dan, Aubrey,Rodney, and Bill are saying. My own suggestion for finding the shortest distance was too simplistic. I had indeed missed something, by ignoring the possibility that under some (but by no means all) circumstances the great-circle path between X and the end-points could take the vessel nearer the pole than X is. Thanks to the others for pointing it out. I think Bill Noyce's suggestion of solving the problem by using a gnomonic chart is the best approach. It is clear that the direct great-circle course beteen start and destination is quite irrelevant if it crosses the latitude limit, and in that case there's no point in following that great-circle anywhere at all. For this second shot at it, I addressed the problem by using an analogue computer, being a piece of string and a globe of the Earth. The globe is in the form of a blow-up beach-ball, 18 inches in diameter. Made in China, it's somewhat geographically challenged. For example, the passage between the Faeroes and Iceland has, for some reason, been labelled "Damascus", and the outlines of continents and islands don't give confidence in any great accuracy. It's only a beachball, after all. However, if I went in for ocean sailing (which I have no great yen to) I would pack that beach-ball (deflated), and the piece of string, in the navigator's toolkit, to provide a rough solution to such navigational questions. From the 15th century, right up to the 18th, the "use of the Globes" was something that mariners were taught, and distances and altitudes were derived by measuring across the globe's surface with dividers, to some low precision. The other globe was of course the Star Globe. ------------------------------ george@huxtable.u-net.com George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. Tel. 01865 820222 or (int.) +44 1865 820222. ------------------------------