[Squeakland] More thoughts - Re: Demoing Etoys to kids

Alan Kay alan.kay at squeakland.org
Sun Aug 12 12:42:45 PDT 2007

Hi Stephane --

At 12:11 PM 8/12/2007, stéphane ducasse wrote:
>Hi alan
>I always liked the way ancient measured pyramid using the shadow of a
>know piece of wood and use Thales theorem.
>At least it was a really practical example, I used to teach Thales

Yes, and it is even simpler for the children to 
think just in terms of similar triangles.

>>For example, if we occlude a quarter with a dime and measure this
>>carefully, we see that the distance in diameters has to be the same.
>Now I do not understand the "distance in diameters"

Check the picture. If it is 9 dimes from the eye 
to the dime, it will be 9 quarters from the eye 
to the quarter. If it is 110 quarters from the 
eye to the quarter that occludes the moon, the 
moon is 110 moon diameters from earth.

>>And if we then occlude the moon with a coin (as Aristarchos of
>>Samos indeed did!) we will find that it takes about 110 coin
>>diameters, and this means that the moon is 110 moon diameters away
>>from us!
>How do we get 110?

You measure the number of coin diameters from the 
eye to the location of the coin that occludes the moon.



>>  Children love this (too bad adults don't, or they would know about
>>this and teach it to children).
>Some do :)

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