From Wuwalton@aol.com Sun Aug 28 11:38:55 2005
Date: Wed, 2 Jul 2003 13:45:49 EDT
From: Wuwalton@aol.com
To: wsanford@wsanford.com
Subject: Re: Shadow Sharpening/The Analemmatic Sun Compass 

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Walter,
      I decided to rewrite my directions separating the conflicting
directions for the use of a "pinhole" in the ceiling from the directions
for a "ball on a flagpole."
     First, I assume that for an inside analemma you are using a
"pinhole" in the roof or window of a building  The center of the fuzzy
spot of light on the floor may be approximated by use of a second pinhole
(say 1/8" diameter) in a 3"x 5" card. Hold the card in the spot of light
a few inches (4" to 12") above the floor.  You will see on the floor a
small pinhole image of the original "pinhole."   Mark the position of
this image spot while the original spot of light is kept centered over
the hole in the card. This may require the assistance of another person.
 If the card is kept perpendicular to the beam of light making the image,
it is relatively easy to keep the spot of light on the card well centered
over the pinhole in the card.  If the card is thumbtacked to the edge of
a small board that moves over the floor, and the card bent to be
perpendicular to the beam, this process is made more easy.
      Second, if you are using a vertical pole (flagpole?) with a ball on
the top for marking or reading an outside analemma, the center of the
fuzzy shadow may be approximated by use of a pinhole (say 1/8" diameter)
in a 3"x 5" card. Hold the card in the fuzzy penumbral shadow.  (If the
card shows the dark central umbral shadow this will not work.  Move
farther away or decrease the size of the object casting the shadow.)
 Hold the card a few inches (4" to 12") above the surface on which the
analemma is drawn or is to be drawn.  You will see on the surface a small
pinhole image of the ball.  Mark the position of this image of the ball
while keeping the image of the ball centered in the bright area of light
that surrounds it.  
      I hope this clears up the difficulty of reading about two processes
at once. Let me know how it now reads.  Please tell me something about
where you are making this analemma, whether it is from a shadow or a spot
of light, and how high above the surface the hole or ball casting the
image is.  Good luck
     Bill Walton
     Plymouth,  MA, USA
     42 N   71 W