> > It seems to me it would work, but I can't see any > > advantages over a cylindrical gnomon. > > I just tried the shadows of a knife edge and of a > 3/4" diameter rod and they look about equally sharp. > I should do a more careful experiment, but to first > order, it appears to be true.
Indeed so, at equal distances you get equal fuzz, but this misses the main point... With a rod you can readily estimate the centre of the shadow ignoring the (approximately equal) fuzz on either side. With a knife edge you have to estimate where in the fuzz is the true centre-line of the shadow of the edge. This is error prone and, to some extent, subjective. I say `spare the rod and spoil the sundial'. Frank King Cambridge, U.K. --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
