Hi John, Frank and all, As Frank says, it is largely the angular width of the effective sun that causes the major error. On hazy days the brightness versus angle from the center of the sun widens out, sometimes drastically. Using Frank's wall example, as the haziness increases, narrower wire gnomons ( or finger shadows ) begin to disappear and the doubling he mentions occurs with the finger tips further apart. A truncated cone will help somewhat. I've not tried it, but a truncated cone capped by a hemisphere of the same diameter of the truncated end would seem a good compromise, and somewhat safer as well.
What have the rest of you folks in hazy climes discovered on this? Let me know what you discover John, and thanks for the neat stuff! P.S. Has anyone built a sundial using longer wavelength radiation from the sun that would penetrate haze and even clouds? Edley McKnight On 9 Aug 2006 at 8:10, John Carmichael wrote: > Hi Edley: > > Well you learn something new every day, especially from the smart people on > this List. > > I had no idea that a hazy day would shorten the shadow cast by a cone's > point! In fact, I still don't quite believe it until I get to see it with > my own eye's. It's our rainy season so we might get a hazy day. I will use > my experiment and will test all the gnomons on the next hazy day. I'm > wondering if the shadow shortening is greater with longer shadows when the > sun at a low angle (I bet it is). And by how much? Is it really > significant? > > Also, does the width of the cone or point make a difference? Wouldn't a fat > cone's shadow be less susceptible to this effect? > > Has anybody else observed this effect? > > very interested in this, > > John > > > ----- Original Message ----- > From: <[EMAIL PROTECTED]> > To: "John Carmichael" <[EMAIL PROTECTED]>; "Sundial List" > <sundial@uni-koeln.de> > Sent: Monday, August 07, 2006 10:26 PM > Subject: Re: Expanded Nodi Shadow Experiment > > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
