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    Why is a sextant like it is?
    From: George Huxtable
    Date: 2004 Nov 17, 19:54 +0000

    This may be a silly question, in which case some pundit will explain why.
    
    Every sextant I have seen, or seen described or pictured, has a similar
    form. The observer looks horizontally through the telescope, at the
    horizon, through the part-silvered horizon mirror. The celestial body is
    viewed, by reflection in two mirrors, brought down to the horizon by moving
    the index arm.
    
    And yet, for some applications, it's useful to use the sextant upside-down,
    pointing the telescope at a star, and working the index arm to bring the
    view of the horizon (as seen in the "index mirror") up to it. That makes it
    easier to identify the right star of a constellation, because the observer,
    and his telescope, and his left eye also, are looking up directly at it. In
    that case, a pair of open sights could be attached to the telescope, for
    easy preliminary sighting without magnification. Then, after identifying
    the star in the telescope, it could be kept in view while the horizon (and
    there's only one horizon, so never any difficulty in identifying THAT) is
    brought up to meet it.
    
    The trouble is that no sextant that I know of has been designed to be used
    that way, so the handles and knobs are all in completely the wrong place.
    That in itself is enough to discourage the use of a sextant "upside-down".
    
    I can see one advantage to the "normal" use of a sextant, in that the
    observer always looks in a horizontal direction, which is comfortable for
    him. Use in "upside-down" mode requires him to look up into the sky, which
    might be an uncomfortable posture, especially if the altitude was great. Is
    that the only reason (or the dominant reason) why EVERY sextant is made the
    way it is?
    
    Has any maker ever experimented with a design which would make it easier to
    use a sextant "upside-down", or better still, either way, perhaps by
    providing an additional handle and an extended adjustment knob? That, by
    the way, would also ease the measurement of lunars.
    
    I only ask...
    
    George.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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