|The Platform Heliodon simulates sun and shadow patterns in a manner reflecting the changing geometric relationships between
the earth and the sun as seen from space. From this perspective the sun is relatively stationary and the earth (and table) orbits, rotates, and tilts in relationship to this “fixed” sun position.
As a first step in using either heliodon, it is important to identify the site location of the project in question and to set the instruments to reflect the appropriate latitude. Obviously, as one moves from the equator toward the North Pole, the higher the latitude the lower the apparent track of the sun would be across the sky. This is true year round. In fact, this is dramatically illustrated in that at the North Pole, some six months of the year the sun "never sets" and for the other six months of the year, the sun "never rises". These extreme conditions which result from being tilted toward the sun and being tilted away from the sun are unique at this location. Monthly Brackets-
Once the latitude has been fixed, then the challenge is to look at the relative effects of the track of the sun at different months of the year. Typically, such examination is "bracketed"- one looks at the lowest altitude arc (the winter, December 21) and the highest altitude arc (summer, June 21) and then the more balanced time of year (the equinox, September and March 21). These represent the ranges of the solar path through the skyvault and help one to see the seasonal difference of a winter influx of shadow casting sunlight as compared to the summer influx of such beam radiation. Within each month, of course, it is important to also bracket the influence of time considering the 15° per hour incrimination of the sun across the skyvault year round. Hourly Brackets-
By convention, most solar studies will look at the 9:00 a.m. to 3:00 p.m. period as a window of time during any given day, winter or summer, wherein the thermal radiation and illumination intensities are at their higher values. It is important to note that many architectural drawings showing sun angles in section are typically "cut" at the noon hour, and while this is a helpful illustration, this is the one moment in time when the sun is at the highest altitude. For the many hours before that moment and the many hours that follow, the sun is never at such high altitude and of course is at increasingly angular relationship to the building in plan. This illustrates that the Earth/sun relationship is truly a three-dimensional relationship and is best studied in model form. This plan/angle relationship is referred to as the Zenith Angle. Typically, due south is considered 0° and each hourly (15 °) increment, either east or west is considered 15 °, 30 °, 60 °, etc. east or west of the south meridian. Thus, we would see a description saying that the sun rises 60 ° east of south or sets 60 ° west of south during the winter at the 40 ° north latitude.