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    Re: Lunar Distances with Alex's SNO-T
    From: Alexandre Eremenko
    Date: 2006 Nov 1, 23:24 -0500

    
    Bill,
    
    > I recall Frank posting the method,
    > but never quite grasped the principle.
    > Why do we need 500 feet?
    
    I wonder where Frank does it in Chicago:-)
    I am thinking more of outdoor places,
    like Celery Bog, etc.
    500 feet we need because the angles involved are
    very small.
    Indeed, suppose your IC is 0.1' and you want to detect it.
    the distance between the sextant mirrors is
    about 2 inches. The two rays inclined at 0.1'
    issued at a distance 2 inches will be still 2 inches
    apart if you walk moderate distance from the sextant.
    So you see nothing.
    You have to walk far away for the rays to diverge by
    2.1 inches, so that you can see the difference.
    Simple computation shows that for this you have to
    walk 260 feet away. But the difference between 2 inches
    and 2.1 inches is quite small... So it is better to walk
    twice that much.
    
    Alex.
    
    
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