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    Re: Why is a sextant like it is?
    From: Gary LaPook
    Date: 2004 Nov 17, 20:32 -0800

    Of course you can use the sextant right side up and accomplish the same
    thing. Just set the index on zero and look through the telescope at the
    star. Then slowly move the index arm at the same rate that you move the
    sextant to the horizontal position while keeping the star in sight in
    the mirror through the telescope  until the horizon comes into view.
    Then perfect the setting and take the reading.
    
    gl
    
    George Huxtable wrote:
    
    >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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