Greetings wonderful dialers all ! Regarding Phil Pappas suggestion that the true shadow point is in the center of the prenumbra, I still have doubts.
I haven't had time to make a shadow sharpener to see if the point is in the perceived center or not, but in the meantime, I was wondering if anyone could show, mathematically/graphically, the increasing intensity of light as one moves from the darker edge of the penumbra shadow to the lighter edge, and to show at what point on this curve of increasing light the sun would be bisected by the gnomon? I suspect it is closer to the darker edge rather than the center. As a point of interest, I read that the Shadow Sharpener was used to precisely locate the noon shadow of the tip of a tall vertical gnomon several days before and after the solstices. With these points accurately plotted, it was then possible to interpolate the exact time that the solstice occured, even if it happened at night at the observer's location. Charles
