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Isonomia wrote:
> As a separate question to my other post, I want to use a sextant on
> land to demonstrate to children that you can locate your position with
> the sun.
>
> The obvious first problem is getting an accurate fix on the "horizon",
> and  the obvious answer (even without a book) was to use a reflection.
> All good in theory, but in practice it is full of problems.
>
> 1.  there is the problem of keeping a bowl of water still with kids
> jumping up  and down,
> 2. trying to get children to stay one position long  enough to keep
> the reflection in view
> 3. using the filters makes it even worse because they can't see the
> bowl of water and  the sun's reflection is quite a bit darker.
>
> Eventually for my younger child  I tried setting up a plank in the
> garden and tying the sextant up with  string to give a level, but the
> darn sun moved so quick that it ran off the  end before I had a chance
> to set it up with any accuracy. I'd appreciate any ideas!
>
>   
Perhaps making a simple quadrant would do for the kids and instead of 
using two visors to look through you could make one with one small open 
visor and a larger closed one to cast the smaller visor's shadow onto 
the larger (so they do not have to look at the sun). After that exercise 
you can explain that a sextant does a similar job using two mirrors.
> Refraction errors on false horizons
>
> The great advantage with a false horizon for children (as opposed to
> the sea), is that there is no need to pay for icecreams! AKA, taking
> the children to the sea side - but  more importantly there is no need
> to know the size of the sun, the height of  the waves, the height of
> the person or anything else like that as they all  cancel out.
>
> The great disadvantage is that you still have refraction through the
> atmosphere (though not of the horizon!) and the only table I have
> doesn't  list refraction of the horizon separately from that of the
> direct view of  the sun so I would appreciate some information on this
> error!
>   
Last post on refraction in this list was NavList 3850 (check the 
archives at http://fer3.com/arc/sort2.aspx?y=200711md), giving three 
different formulae.

Nicol�s


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