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    Re: Latitude and Longitude by "Noon Sun"
    From: Frank Reed CT
    Date: 2005 Jun 6, 22:53 EDT

    Fred you wrote:
    "In response, I don't find  the intercept method any more difficult to
    understand geometrically than a  noon shot.  The basic flag pole
    analogy, much derided here, seems  adequate to me, only requiring that a
    spherical surface and infinitely tall  pole be substituted to achieve
    reality.  While building the infinitely  tall pole, an instructor would
    get to talk about parallax."
    
    Yes, I  totally agree that the essential principle of the circles of position
    crossing  is very easy to explain and that a substantial majority of people
    who hear such  an explanation do understand it. I've explained it over a
    thousand times (I'm  not kidding!) within the past few years to casual tourists and
    groups of  children as young as twelve years of age. And they get it, and
    they're happy wit  the explanation. But it's a long haul from that quick
    geometrical explanation to  the end goal of actually using the Nautical Almanac and
    sight reduction tables.  How long did it take you to learn so that you could do
    it for real? How long do  you think it would take someone a lot less
    mathematically inclined than you  are?
    
    On a general note, let's remember here -- I have nowhere suggested  that
    everyone should throw their sight reduction tables and Nautical Almanacs
    overboard. First and foremost, I felt it was important to counter the erroneous
    claim, which I think you agreed with, that a navigator could not get a good
    longitude at noon. Second, I am presenting a method of celestial navigation  --and
    it IS *real* celestial navigation-- that can be taught practically to  students
    in a very short period of time. They can have almost instant  gratification.
    And for a dying art, that's not such a bad thing.
    
    And:
    "Using pen and paper methods of sight reduction, LOP navigation  is more
    difficult, but not with a calculator or computer."
    
    Very true  about a computer especially. If you're reducing sights with a
    computer, why not  just use GPS? Clearly for practice sights, it's a nice
    convenience to clear them  with a computer. And there are some enthusiasts who like
    going through the  motions of using a sextant and doing all their clearing work
    by computer, and  the fact that they have no idea how to clear the sights by
    hand doesn't matter  to them at all. That's simply another market segment.
    They're not "navigating"  with celestial, but they like using sextants. To each
    his  own.
    
    And:
    "George's comments about taking a prolonged series of sights  while
    underway are well taken."
    
    Nah. This is not time-consuming.  Taking six to ten shots over 40 minutes to
    an hour would require only six to ten  minutes of work. You could make lunch
    for a whole family at the same time. And  besides, if you're not in a storm or
    a race, there's an awful lot of free time  on most ocean passages. Ask Joshua
    Slocum...
    
    And:
    "a clear sky is  needed.  Why not take a quick morning, noon and evening
    shot?"
    
    Yes,  a clear or partly cloudy sky is needed. Note that you don't need to see
    the Sun  continuously for this method --occasional "peeks" will suffice. Of
    course,  cloudy weather is the best argument against using celestial navigation
     generally.
    
    You also wrote:
    "One point about a traditional noon shot is  that the sun often peaks out
    from behind the clouds at noon for a few moments  even on days with
    heavy overcast.  There is a story famous to me about a  passenger on a
    ship asking why all the officers had their sextants out under  a cloudy
    sky at noon, only to be informed by the captain that the sun  often
    would peak out for a bit, and sure enough it did.  That's also  been my
    experience at 36N in the mountains."
    
    I think this is an 'urban  legend'. I would bet that the rate of "Sun
    peeking" on mostly cloudy days is  constant throughout the middle hours of the day
    and navigators have tended to  remember those times when they got lucky right at
    noon. I think a cloudless  longitudinal stripe along the Sun's longitude
    (which would exist if this tale  were true) would show up pretty clearly in
    satellite imagery!  
    
    -FER
    42.0N 87.7W, or 41.4N  72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
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