Pete Swanstrom <[EMAIL PROTECTED]> writes: > I have built two such sundials, which indicate the time and date > accurately to within the minute and the day. They also quickly adjust > for Daylight Saving Time. I have created a web page with a description > and pictures of both dials, including the method, calculations and data > I used for their design. Hope you find this useful.
I like your work, both with respect to the craftsmanship and the mathematics, but I think you're over selling the result. Near the equinoxes, the sun moves about its own diameter from day to day, so it is possible to read the date accurately, but near the solstices, the N-S movement slows to a stop, so you would be doing well to read the date with an accuracy of a week. This is plenty good enough to figure out when to start your seedlings, but not to plan your Christmas shopping. Near the winter solstice, if you know the date, you can find the the time within a minute, and if you know the time, you can find the date within a day (or two), but it is difficult to determine both from observations of shadows. Near the summer solstice it is even harder, since the equation of time changes more slowly there. Art Carlson [EMAIL PROTECTED] http://www.ipp.mpg.de/~Arthur.Carlson/home.html