NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lat/Lon by "Noon Sun" & The Noon Fix PROVE IT
From: Frank Reed
Date: 2009 May 12, 11:42 -0700
From: Frank Reed
Date: 2009 May 12, 11:42 -0700
Brad, you quoted: "Report of the Secretary of the Navy 'We recognize in navigation two classes of astronomical problems; one possessing perfect accuracy of computation; the other uncertain, and approximate only in its results. The first class is, of course, always employed when the weather and other circumstances are favorable. The second class of problems, that which gives only approximate deductions, is never resorted to except from necessity.' " When I read this, I thought I recognized it and recalled that it was from an era somewhat before the modern understanding of error in observations and calculations. Sure enough, it's the report from c.1865. What's written here wasn't true then, and it isn't true today. The text per google books is slightly different and reads: "We recognize in navigation two classes of astronomical problems; one possessing perfect accuracy of computation, *** and admitting no other error than the probable error of observation***; the other uncertain..." etc. That one extra phrase (between the ***'s) helps a bit since, of course, there's no such thing as perfection in any observational activity, but it's still misleading. There are NO problems in nautical astronomy that possess "perfect accuracy of computation" though there are certainly different levels of accuracy in different computations. The report was referring to von Littrow's method of finding apparent time incidentally. Chauvenet also wrote about this in "Astronomy: Comprising Instructions to Naval officers" which you can read on google books here: http://books.google.com/books?id=KWUpAAAAYAAJ This article has some good material, some not so good. Chauvenet was a land-based mathematician --influential in the U.S. Navy and highly respected, but idiosyncratic in his beliefs. Of lat/lon by noon sun, you wrote: "I would like to assign the latitude and longitude by the noon sun fix to the second class of problems. It can provide us with a useful figure of merit, albeit without perfect accuracy. Certainly, with a least squares curve fit, the method affords us a very reasonable fix." It's a fix, not different except in degree from any other fix in celestial navigation. It is a running fix, and therefore it is somewhat dependent on errors in estimating the vessel's true speed. It is a statistical fix, and therefore there is an error ellipse around the position. But note that ALL running fixes in celestial navigation are somewhat dependent on errors in true speed. And ALL fixes have error ellipses around the position. ALL fixes are "without perfect accuracy" to use your phrasing. Oh, and the other thing about this approach to getting a fix at noon is that it's easy to teach, easy to learn, and, as I cannot emphasize enough, easy to re-learn if that day comes when you really need celestial. "Easy" is a dirty word for some fans of celestial. Some folks, equally worthy of our attention as educators, are in it for the intricacy and the delight of a tricky puzzle. They're a different market. And you concluded: "Proven?? A resounding YES!" Well, I'm glad you think so. Have you tried it out yet? :-) -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---