Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Lat/Lon by "Noon Sun" & The Noon Fix PROVE IT
    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:
    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? :-)
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site