Re: Re: Shadow Sharpener

[Wuwalton]

      Thanks for trying out the "pinhole" method.  (I've been trying for two years to get someone to try and appreciate the precision and beauty of this technique.)  
      After I sent the last message it dawned on me that at your giant sundial you could have a three legged stool on casters that supported the pinhole.  This stool could be moved around until it was on the edge of the penumbra and the time read with precision and hopefully, accuracy.  It does not matter that the disk with the pinhole would not be perpendicular to the incoming rays of the Sun.  In fact, having the disk parallel to the surface below, insures that the image of the Sun will be a circle and not an ellipse.  The size of the "pinhole" may be adjusted to give a sharp, bright image for different heights above the dial surface, greater heights requiring larger "pinholes."
      I'm not sure about your noon table.  It must be a completely separate instrument, and not on the local noon line of the telescope sundial, otherwise the shadow of the telescope would cover it at noon.  If it is separate, there are many ways to handle it as a "noon mark."  One of your "bead in a hole" shadow sharpeners could cast a spot on an analemma with dates and times on it to read the instant of mean time noon or standard time noon.  By reading when it crossed a meridian line it would indicate the instant and date of local noon.  I made a small noon mark once that had both a date scale along on side of the meridian and a "time of local noon" scale along the other side.  Viewers found it interesting.
      Best wishes on the success of your proposal!


     Bill Walton
     Plymouth,  MA, USA
     42 N   71 W

Please note my new e-mail address:  [EMAIL PROTECTED]