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    Re: Children's land-locked "Sextant"
    From: Geoffrey Kolbe
    Date: 2007 Nov 27, 20:41 +0000

    I had the pleasure of visiting David Burch last September at the Starpath
    headquarters in Seattle. David had a sextant very similar to the one
    described here by Bill and we took it outside to take a sighting of the
    sun. After heading back inside to reduce the sight, we were only about 8
    minutes out. A very impressive demonstration on what can be done with such
    a simple instrument.
    
    If I were trying to introduce a bunch of 11 year olds to the ideas of
    celestial navigation, I think this would be the route I would take.
    
    Geoffrey Kolbe
    
    
    
    At 15:46 27/11/2007, you wrote:
    >
    >
    >This may not give the level of precision you're looking for, but it's
    >simple and easy for kids to understand:  Make a quadrant out of
    >cardboard.  Print the protractor with a laser printer, either directly
    >onto light cardboard, or onto paper that you glue to heavier
    >cardboard.  Make sure the zero is parallel to one edge of the
    >cardboard.  Cut around the arc so you have a quarter-circle, or a
    >half-circle, or something in between.  Poke a tiny hole exactly at the
    >vertex, and insert a thread.  Tape it in place on the back, and tie a
    >weight (I used washers or nuts) so the thread hangs taut just below
    >the arc.  Tape a drinking straw along the edge of the cardboard for a
    >sight, so it is supported by the edge like this:  O==  To sight stars,
    >you look through the straw with one eye, and around it with the other,
    >and place the star at the center of the circle.  Rock the quadrant
    >until the stationary thread just grazes the cardboard, pinch it in
    >place, then read it.  You should be able to read to 15' or better with
    >a reasonable-sized scale, though your sights will likely have more
    >scatter than that.  For the sun, don't look through the straw --
    >instead, watch the quadrant's shadow, and point the straw at the sun
    >until its shadow becomes an "O".  Again take care that the quadrant is
    >in the vertical plane, and pinch the thread.  (This measures to the
    >center of the sun, not to either limb.) You should check each quadrant
    >for index error -- assuming your printer is properly adjusted, and the
    >thread pivots in the center of the arc, other errors should be
    >negligible.  Good luck!
    >     -- Bill
    >
    >On 11/27/07, Isonomia  wrote:
    > >
    > > I'm camping next summer with a load of 11year old kids and wanted to
    > > do some celestrial navigation and plot a position to within
    > > 10-20miles.
    
    
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