I just finished writing a tidy little program that calculates when the sun is exactly south (or north), east and west for any given date and location. I wrote it to help mark a cardinal direction for laying out analemmatic dials, but it can help orient any sundial. Using the vertical string method, an east west line is much easier to mark than a north south one, because the sun is lower and so the shadow stays sharp over a longer length.
Of course, an east west shadow can occur only in the summer half of the year for people outside the tropic zones (most of the folks on this list). For people within the tropic zones, the an east west shadow will not form near the summer solstice either. And for the unfortunate sundialist who lives on the equator, an east/west shadow can occur on only 2 days of the year--the equinoxes. Download CardinalDirections.exe from www.precisionsundials.com/software.htm, and let me know what you think. -Bill Gottesman -
