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    Re: The Noon Fix
    From: Frank Reed
    Date: 2009 Apr 8, 12:00 -0700

    George H wrote:
    " But his posting raises a few questions in my mind."
    
    Again... :-) 
    
    George, by focusing on very small details, you are throwing out the proverbial 
    baby with the proverbial bathwater. One can, in fact, apply this seemingly 
    "heretical" method of getting a fix with excellent results. You've really 
    missed out by not investigating this further.
    
    Of Jim's book, you wrote:
    "One problem is that, presumably, he reserves the details of his arguments to
    his book, perhaps in order to encourage us to buy it, but that inhibits
    informed on-list discussion of his points."
    
    NavList is surely not the target market for such a book. Jim, you do whatever 
    you want, but be careful not to fall into the trap of posting the material 
    contents of your small book on the net just for the amusement of us on 
    NavList. While NavList members are likely to be able to help spread the word 
    regarding your book, this is not the primary market for it.
    
    So what IS the market for this type of navigation? I would suggest that nearly 
    anyone new to sextants in this GPS age should learn this method of navigation 
    (or one of its variants) FIRST. It's easy. It's reasonably accurate. And it 
    takes the student from first sights to a fix in latitude and longitude in the 
    shortest possible time. Additionally, and importantly, it's very easy to 
    re-learn this technique in just a few minutes. A navigator who has learned 
    "latitude and longitude by noon Sun" has the fundamentals in hand and, if 
    desired, the full methodology of line of position navigation and its many, 
    many variants can always be learned later. 
    
    And George, you wrote:
    "What is hidden, under that catchy title of "The noon fix", or "longitude at 
    noon", is that it's actually longitude AROUND noon"
    
    But everyone knows this, George. It does not detract from the method in any way. 
    
    And:
    "comparing observations over a time span that extends well before and well 
    after noon. The shorter that time span is, the less accurate is the result. 
    Unless that time-span is a well-extended one (Bowditch recommended 30 minutes 
    each side of noon), then "longitude around noon" becomes impractical, a fact 
    that its proponents often gloss over."
    
    The focus on time interval, here and in Bowditch, may be misleading. What 
    matters is a change in the Sun's azimuth (just convert the method to its 
    equivalent lines of position to see why). For reasonable accuracy, one should 
    take sights over a sufficiently long period such that the Sun's azimuth 
    changes by roughly twenty degrees. When the Sun is fairly low in the sky, 
    that's fairly close to the suggested "30 minutes" on each side of noon. But 
    when the Sun is higher, the time interval can be quite a bit shorter.
    
    Also, just from the standpoint of terminology, the idea that you have to take 
    sights over a somewhat extended period to get longitude near noon is really 
    not that different from the common procedure for getting latitude at noon. 
    Most students, when learning the LAN sight, are taught to take occasional 
    sights leading up to noon and then catch that moment when the Sun "hangs" at 
    its maximum altitude. So even for latitude, it's really latitude "around 
    noon". The difference for the longitude case is that we also want some sights 
    after noon to make a complete noon curve.
    
    -FER
    PS: And while we're at it, for those who haven't heard of it, among Hewitt 
    Schlereth's numerous books on navigation, there is "Latitude and Longitude by 
    the Noon Sight" which is occasionally available from used book dealers on 
    abebooks.com, ebay, etc.
    
    
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