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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.

Has anyone ever built a simple theodolite type sextant out of basic
DIY material and managed to obtain an accuracy that would allow a
basic position plot and if so how?

In particular I would like to build a form of "sextant" based on
measuring the angle above a horizontal plane of the sun using the
sun's shadow.

I'd welcome comments, suggestions or practical experience on:-

1. How to create a horizontal plane to within a few minutes accuracy?
2. How to obtain a good shadow/image, e.g. has anyone tried glass
lenses?
3. How to measure an angle from the horizontal to the sun's image to a
few minutes?

All contributions greatfully received.

Mike


HISTORY & WHAT I'VE STOPPED CONSIDERING

I started by considering using a sextant with an artificial horizon.
However, whereas it is a skill to find the sun and line it up with the
horizon (sea=go up, sky=go down), trying to line up two images of the
sun is an art. And aligning two images of stars is so difficult I've
only managed a sensible result on 50% of my tries.

My next idea was to use a real artificial horizon, in the shape of a
string set at a distance to give a low arc error. However, after a bit
of calculation regarding the distance (30-100m) and the length of the
string (10-30m), I've realised that any string big enough to see is
going to dip considerably unless it is under such extreme tension that
it is a positive hazard in an open area.

I then considered laser levels - but I'm not looking through a sextant
with potential laser reflections all over place - even if one could
see the laser line in daylight at the distance required.


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