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Hi Richard:

It's about 15 feel long and a few feet wide as far as I can remember.
Where the hole is at the base of the skylight might be above the floor by 12 -15 feet.
In the winter when the slant distance is long the image is dim so the white 3x5 card makes it visible.
I tried a number of different hole sizes.  It's like a f-100 lens and you get an image of the sun on the floor.  As the hole gets larger the image gets brighter and fuzzier.

Have Fun,

Brooke Clarke, N6GCE

Richard M. Pisko wrote:

On Sat, 9 Aug 2003 22:52:32 -0700, Brooke Clarke wrote:

  

I did not file down the tacks.  The heads are a little less than 1/8"
diameter and were seated so only a tiny fraction of an inch was sticking
up.  You can feel the head with you fingers.  No problem to walk on them
bare foot.

    

That was my first thought; yes.  I'm glad it's not a problem, and I
read the description so it seems as though it would be rather nice.  I
couldn't quite make out the drawings on your ... calculations, I think
it was.

  

I made one of these by placing a metal plate at the lower end of a South
facing skylight and using a 3x5 card with a number of concentric
ellipses and a small hole at their center.  I just tracked the Sun's
image with the card and at exactly noon stopped and drive a small brad
nail into the hardwood floor.  After many years there would be more than
one nail for the same date because as we go through the 4 years of the
leap year cycle the timing is a little different.
        

I see the reasoning behind the series of ellipses on the (much
handled) 3x5 card; to more closely match the sun's shape on the
horizontal floor.  What are the rough dimensions of your analem...
figure "8"?

I guess I could calculate that, given the difference in elevation
between the skylight aperture and the floor, as well as your latitude,
but I thought a reality check might be a break from the theory.  :-)


--
Richard ...