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    Re: Irradiation and manual navigation
    From: George Huxtable
    Date: 2010 Mar 13, 19:36 -0000

    Frank wrote-
    
    "As for Chauvenet, he had almost no experience in navigation. Though he was
    an exceptionally competent and meticulous mathematician, why would you trust
    his numbers on something like this? Are his works Scripture?? "
    
    This is not the first time that Frank has made such a statement about
    Chauvenet, in dismissing his views. I would like him to provide the evidence
    on which it is based.
    
    And if, as it should, experience in navigation is the thing that matters, I
    ask Frank to outline his own such experience, so that we can weigh up his
    own worth against that of Chauvenet.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Frank Reed" 
    To: 
    Sent: Saturday, March 13, 2010 7:04 PM
    Subject: [NavList] Re: Irradiation and manual navigation
    
    
    Henry, you wrote:
    "Isn't it really amazing how we seem to keep re-inventing the wheel. Didn't
    our "land bound" Professor Chauvenet give us the exact same number, i.e.,
    +/- 10 arc seconds, in an 1868 paper on Astronomy - admittedly, however, he
    doesn't mention the matter of irradiation. Most of this stuff can be found
    in the literature of yesteryear."
    
    Apples and oranges?
    
    If anyone ever tells you that you should expect +/- 10 arcseconds in sextant
    observations with no further qualification, you should immediately ask,
    "what observations? what type of sextant? what telescope magnification? how
    many observations averaged?" There is no absolute number for the expected
    accuracy of observations, but there are some limits. The limit of the human
    visual system for standard resolution tasks (not vernier tasks) is about one
    minute of arc, slightly better in excellent conditions. If an observer gets
    unit magnification results for standard celestial navigation tasks
    un-averaged that are significantly worse than that, THEN something is wrong.
    Maybe the horizon is poor. Maybe there is some sort of operator error. Maybe
    even that ghostly apparition known as "Irradiation" is at work. Or maybe
    it's just a bad sextant.
    
    As for Chauvenet, he had almost no experience in navigation. Though he was
    an exceptionally competent and meticulous mathematician, why would you trust
    his numbers on something like this? Are his works Scripture??
    
    -FER
    
    
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