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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Ex-Meridian Exercise
From: George Huxtable
Date: 2010 Dec 28, 10:24 -0000
From: George Huxtable
Date: 2010 Dec 28, 10:24 -0000
On 26 Dec, Byron wrote, under the thread "USCG exam memories"- "On the OUTPOST AGR 10, A few of us would see how good we were by using Ex Meridian as LAN and work the sun line for about a 7 degree intersection fix.they were the only way for one shot fix. It was more for fun and a coke bet for the closest to what was thought to be our position DR. from Loran A and other sunlines." That puzzled me, rather a lot. There is no way to get a fix, finding latitude and longitude together, two unknown variables, from a single observation, a "one shot fix". But Byron didn't go into any detail. But now, Greg tells us that he has actually done the same job in practice. He has plotted the lat and long which resulted from a single altitude taken nearly half an our from local noon. That needed to be taken more seriously. Either my own preconceptions were quite wrong (which is always possible) or there was a logical flaw in Greg's procedure. I think there was a logical flaw, on the first page of his calculations, in- http://www.fer3.com/arc/imgx/IMG_0883.JPG in which he states - "LAN precalculated to 32º 32.3' at 11:58:00 LMT, 19:58:00 GMT." How was that obtained? Presumably, by assumimg one of the two quantities he was trying to determine: his longitude. I take it that he fed in to that precalculation a longitude of 119º 13.5'W. And so, it's no surprise that his end-result turns out to be close to that same longitude. So I suggest that Greg repeats his calculation, but feeds in to the precalculation for LAN a different presumed longitude, to see what results he comes up with. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================= ----- Original Message ----- From: "Greg Rudzinski"To: Sent: Tuesday, December 28, 2010 1:41 AM Subject: [NavList] Ex-Meridian Exercise Today was a fine Southern California winter day and perfect for this ex-meridian exercise that Byron Franklin has been talking about. Four standard LOP Sun lines were taken 28 minutes or so before the LAN. These same four LOP's were worked out as ex-meridians to provide a Latitude to cross each LOP at a very shallow cut (7°). The ex-meridians were reduced by Bowditch table 29 and 30 as well as by formula. There was a small difference between the two sets of reduced results but nothing to be concerned about. Shown by link is a plot of one example of the ex-meridian/LOP fix which to my great surprise was only 2.3 nautical miles from GPS. The three other observations were equally as good. So for those looking for a truly unique celestial challenge then try the ex-meridian/LOP fix shot. It was a lot of fun for me and I hope my working notes aren't too messy to follow. Notice the quality of the horizon in the linked photo. No excuses when looking at a sharp horizon like that. Greg Rudzinski ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ----------------------------------------------------------------