This stack was written as an introduction to sundialling which grew out of an interest in timepieces, typically those of the middle ages. It is free to whomever would like to give it a try. In fact I would like to get some feedback on what people think, new additions to the program, ease of use, etc. The e-mail address is located at the bottom of this field. The program was written on a Macintosh SE so the graphics may be a bit too small for some machines. Below is a brief listing of how to use this program and what it can do.
The main card consists of six fields for inputting your current latitude and longitude in degrees, minutes, and seconds. Any empty fields will default to zero. If you wish to calculate hour lines for your local mean time (explained below) in the continental United States be sure to select the correct time zone for your area. If you do not live in the continental United States or would rather calculate hour lines for your local apparent time, choose the "Local Apparent Time" button. The "Calculate" button begins the calculations for the data on the screen.
When completed, the screen shows how a horizontal sundial would appear if viewed from the top and facing true north. An indicator of the latitude and longitude is also repeated. The hour lines are laid out from 7:00 AM to 5:00 PM. Back on the main card are the hour line angles tabulated in a field. The angles are in degrees measured from the gnomon, the triangular piece which creates the shadow and lies along the true north-south line.
The local mean time is the time which you would read off of your watch or clock. This mean time is actually the apparent time, i.e. the time it appears from the sun, at your standard meridian. In the continental United States these meridians are at 75, 90, 105, and 120 degrees west longitude. All clocks in the same time zone show the same time regardless of longitude. The calculations in this program take into account longitudes which do not coincide with a meridian.
The local apparent time is the time it appears to be relative to the position of the sun. High noon is always when the sun is at its highest point in the sky, so the line for 12:00 noon is always at an angle of 0 degrees relative to the north-south line.
More detailed information on equations and building of sundials is on the next card. Graphs detailing time zones, meridians, and the equation of time follow on subsequent cards.
Please send comments and constructive criticism via e-mail to
