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Mike,

> I'm camping next summer with a load of 11year old kids

And you want the kids to participate in your celestial
observations?

> 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.

As I understand from your message you DO have some sextant,
and your problem is with artificial horizon only.

> 1. How to create a horizontal plane to within
> a few minutes accuracy?

I know three ways of doing this. I list them in the order
of decreasing accuracy.

a) Usual liquid artificial horizon.
It is NOT HARD to catch the Sun
with ordinary sextant and artificial horizon. Not much harder
than with natural horizon.
I can give simple
step-by-step instruction
based on my experience. I never had difficulty catching the Sun.
But at night it is much harder, and I found it almost impossible
with the stars, even if you pre-set your sextant. Accuracy
1' is easily achieved with Sun if there is no wind and there is
a stable platform.
b) Air sextant. Can be bought on e-bay for under $100.
If you are lucky and get a working one, it gives you about 5'-10'
accuracy. Members of this list recommended MKIX, I bought one
for $40 (plus shipping) and I am reasonably satisfied with it.
One advise: if there is a choice, give preference to one
WITHOUT clock-work averager. The thing is useless on land and sea,
and takes almost 1/2 of the weight of the device.
c) "practice artificial horizon" sold by Celestaire for
about $25. This is much worse than an air sextant in preformance,
but fits in your pocket.
d) finally, if you don't have a sextant and don't want to buy a real
one, and 20 miles accuracy is OK, and you are willing to
use Sun only, there is another option which I did not try seriously
myself but my friend Bill did, and with satisfactory results:
a German cardboard make-it-yourself sextant. Bill claims that
he achieved 5' accuracy which I did not verify, but it is reasonable
to expect you can achieve 20'. Its artificial horizon is better
than the Chinese junk horizon mentioned in c).
This sextant is also sold by Celestaire.

Alex.



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