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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: suggestion for a satisfactory celnav narrative
From: Fred Hebard
Date: 2005 Jun 3, 13:10 -0400
From: Fred Hebard
Date: 2005 Jun 3, 13:10 -0400
Bill, An appendix of things that a naive navigator might suppose are good, but really are not, would be helpful. I wouldn't put this in the main section, except maybe to say that noon sun shots are lousy for longitude and to refer to the appendix. A fix gives both longitude and latitude without knowing either first, where the fix is the intersection of two or more lines of position. A pure latitude shot, such as a noon sun shot, also gives a line of position, one that runs smack dab east-west, giving no longitude info. Likewise, a line of position from a body with a due east or west azimuth gives only longitude and no latitude. You have to know GMT to use any shot other than a meridian passage shot, an example of which is a noon sun shot. You learn GMT from a watch, the radio, lunars, occultations, Jovian moons, etc. Fred On Jun 3, 2005, at 12:26 PM, Noyce, Bill wrote: > Perhaps the fact that "longitude by noon sun" comes up so often > is a good reason that there *should* be a discussion of this > method, pointing out why it is a bad idea... > > Is there any other observation that gives longitude without > knowing latitude first? Maybe this is part of its appeal. > > (By the same argument, the advanced version should discuss lunar > altitudes for GMT, and what's wrong with them. I think George's > "parts 1-4" do include such a discussion.) > > -- Bill > > -----Original Message----- > From: Navigation Mailing List > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM] On Behalf Of George > Huxtable > Sent: Friday, June 03, 2005 8:59 AM > To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM > Subject: Re: suggestion for a satisfactory celnav narrative > > > Andrew Corl wrote- > >> For Courtney, I am raising my hand to help with this. Don't know what > I can >> do but here is a list of techniques I feel should be in the manual: >> Dead Reckoning >> Latitude by Noon Sun >> Longitude using a shortwave radio and the noon sun >> Sextant operation and how to determine the elevation above the horizon > of >> the sun, moon, star, and planet >> Sight reduction using H.O. 249 - method I am presently learning >> Sight reduction doing all the math (the "apex of celestial navigation" >> according to Frank) > > As a world-weary old cynic, my opinion is that any offer, saying "this > is > how I think it should be done, and I'm prepared to contribute" is worth > at > least 10 proposals of "this is how I think it should be done, but by > someone else, not by me". So Andrew's suggestions are indeed useful. > > No doubt, he expected a bit of nitpicking about his choice of topics, > and I > am happy to provide it. It relates to his suggested topic- > "Longitude using a shortwave radio and the noon sun" > > Although proposals for timing the moment of noon, by observing the Sun > around noon, reappear on this list at regrettably regular intervals, > the > fact remains that noon is the worst possible moment for doing that job. > Although it's possible to make a crude assessment of the moment-of-noon > by > making an extended set of observations, before noon and after, the only > way > to get a PRECISE value of time-by-the-Sun (and hence longitude) is to > do > so > at a time WELL AWAY from noon, so that the Sun is rising and falling at > a > measurable rate. If Andrew were to rephrase his suggestion to read > instead- > "Longitude using a shortwave radio and a time-sight of the Sun", > then I, for one, would be happy. > > George. > > ================================================================ > contact George Huxtable by email at george@huxtable.u-net.com, by phone > at > 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy > Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. > ================================================================ >