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    Re: Long-range airplane navigation
    From: Alexandre Eremenko
    Date: 2004 Dec 2, 09:32 -0500

    Schufeldt says on this subject:
    "It has been hoped that the high-powered telescopes
    would permit the observation of some fixed stars between
    the hours of sunrise and sunset. It was found that this
    can be occasionally be accomplished;
    however it did not prove generally possible, due to the
    loss of brilliance of the star image caused by the mirrors.
    It seems probable that this difficulty can be overcome by
    redesigning the marine sextant to permit the direct view
    of the star, with the horizon becoming the reflected image."
    
    (Apparently the simple idea to invert his sextant upside
    down did not
    occur to him. But I doubt you can invert a bubble sextant.
    Schufeldt used 16x to 20x power telescopes of 50 mm diameter).
    
    Relating this to another recurrent subject on this list,
    Shufeldt also says that their telescopes were fitted with
    "a reticle at infinity", which is a sort of "wires" we discussed
    much. The purpose of this reticle is to help keeping your eye
    focused on infinity while you look for a star.
    
    He also says that a polariser helps.
    
    The positions of the stars were pre-calculated (otherwise,
    it is of course impoossible to find a star in the sky).
    
    With all this, he says that no real success can be claimed when
    telescopes were mounted on the sextants (for the reason explained
    in the beginning), although Sirius was pickied up low
    on two occasions about 15 min before sunset and Arcturus at
    high alt 26 min after sunrise.
    
    Alex.
    
    
    
    On Thu, 2 Dec 2004, Fred Hebard wrote:
    
    > I was asked an interesting question, which was:  could star shots be
    > made during the day with a bubble sextant?  The intent would be to get
    > more than one line of position during one round of shooting.
    
    
    

       
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