NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: determination of longitude and the prime vertical
From: George Huxtable
Date: 2007 Apr 12, 15:45 +0100
From: George Huxtable
Date: 2007 Apr 12, 15:45 +0100
I hope Geoffrey Kolbe's respose, with Bill's reply, show that the problems that Bill raised in Navlist 2550 are now resolved.. But a minor matter cropped up in that mailing that worries me a bit. Bill quoted some predicted Sun positions, that had come from Andres Ruiz' website. I will refer just to that first set of numbers from his mailing, as follows- | Date: 1 May, 2007 | UT: 20:41:45 | Position: N40 W60 | Hc: 24d 00!2 | Az: 270.00 | LHA: 71d 09!5 | dec: 15d 09!5 I don't have a 2007 Nautical Almanac. But I have compared those numbers with my own predictor, held on a pocket calculator, which differs slightly. That gives a Sun position, at 20:41:45 GMT on 1 May 2007 of 15 deg 09.5' N, exactly as Bill gave it, but a GHA of 131deg 09.8', and so with a long of 60deg W, a LHA of 71deg 09.8', just 0.3' more than the figure Bill stated. That difference isn't a large one, but to me it's a bit of a worry, depending on which of us is in error. I expect the Sun predictions of that program to be generally well within a millidegree. One might expect divergences of 0.1', as a result of rounding errors, but not more. If my program is out by that amount I need to investigate why. So I wonder if Bill will kindly recheck that figure, and ask anyone with a current Nautical Amanac or computed equivalent, to provide a value for Sun GHA at that moment, please. George. contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---