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    Re: Children's land-locked "Sextant"
    From: Mike L
    Date: 2007 Nov 27, 09:26 -0800

    whilst in theory a reflected artificial horizon isn't difficult to
    use, in practice the two suns appearing and disappearing in the view
    finding and moving in opposite directions take quite a bit of patience
    to work out and to begin to get results.
    Whilst I would have no problem instructing an adult, my experience
    with trying to instruct children is that whilst they were
    concentrating they were incapable of accurately expressing what they
    saw in the viewfinder and as I can't see what they are seeing and so
    don't know what they are doing wrong (or even right) I can't help
    them! So the whole thing was frustrating both for me and for them.
    In contrast it will be easy to tell children how to adjust a "sextant"
    using a shadow and set to measure an angle like a theodolite.
    If I do use a sextant, at the very least, I've got to find alternative
    solar filters so that the two images of the sun are different colours.
    That way there is at least a simple way to refer to them: "can you see
    a red sun then ..." - "can you now see a blue sun then ..", "is the
    blue sun above or below the red sun ... turn the knob left/right...",
    A few child friendly instructions:-
    Turn left,
    Turn right
    Look down
    Look up
    Tilt to the left
    Tilt to the right
    Turn the knob clockwise
    Turn the knob anti-clockwise
    When you tilt the sextant from side to side, do they cross so that
    both suns are in exactly the same place?
    Don't you dare drop it on the mirrors!
    On Nov 27, 4:01 pm, Alexandre E Eremenko 
    > 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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