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    Re: Metal versus plastic or better telescope?
    From: Alexandre Eremenko
    Date: 2012 Mar 27, 20:15 -0400

    Lu,
    You wrote:
    
    > Something never discussed is the accuracy achievable --
    > even with the best
    > of sextants -- on the heaving deck of a small craft at sea.
    
    In 2005 I posted my results obtained from a 40ft yacht while sailing
    around England from Kiel. Next year I posted some results obtained
    from a similar yacht sailing in the Baltic.
    
    Of course two 2-week or so trips is not much of experience,
    but my limited experience agrees with what I read in the literature.
    
    Taking a sight from a small boat is very hard, because it is rocking.
    It is hard to catch a star or Sun, it is hard to keep it in view
    for few seconds. In many cases I observed without a telescope, as some
    experienced yachtsmen recommend. In this case the "zero tube"
    probably helps
    but I did not have one. Here is a picture:
    http://www.math.purdue.edu/~eremenko/Navigation/sext.jpg
    
    I agree that 0'3 index error (which my SNO permanently has, for years)
    is totally irrelevant in these conditions:-)
    And one has to wash the mirrors splashed with salt water after every
    observation.
    
    Alex.
    
    
    
    
    
    
    
    

       
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