created by Carl Sabanski
Make a Polar Sundial - Graphical Method
Polar Sundial: is a sundial in which the dial plate is set along the East-West direction and inclines so that it is parallel with the polar axis. The standard polar pointing gnomon is thus also parallel to the dial plate.
Like the equatorial sundial the polar sundial is a universal sundial and can be used at any latitude. To work properly the dial plate must be tilted at an angle equal to the latitude and the style pointed to the celestial pole.
Figure 1 shows the relationship between a polar sundial and the equatorial sundial that is used to create it. Notice that the two sundials have a common style or shadow casting edge that points to the celestial pole. The style is parallel to the face of the polar sundial and it is perpendicular to the face of the equatorial sundial. For this to be, the equatorial sundial is perpendicular to the face of the polar sundial.
This dial is designed for the Northern Hemisphere and the style must point to the North Celestial Pole (True North) or Polaris. To design a sundial for the Southern Hemisphere you need to reverse the numbering of the hours. Instead of the hour numbers going from 6 a.m. to 6 p.m. from left to right they will go from 6 a.m. to 6 p.m. from right to left. Also the style must point to the South Celestial Pole (True South).
This sundial will tell solar time but not clock time. You must learn about longitude correction and the Equation of Time to correct your sundial reading so that it will give you clock time.
Figure 1: Polar Sundial (CAD)
It would be difficult to project the hour lines of the equatorial sundial shown in Figure 1 on to a perpendicular plane to create the polar sundial. A graphical method is available to do this on a flat surface, your piece of paper. Follow these instructions and in no time you will have your very own polar sundial and it will be designed for where you live.
What do you need to know? All you need to know is the latitude of where you live. The latitude is not required to design the dial but to position it properly. Now let's make a polar sundial.
A polar sundial could tell the time between 6 a.m. and 6 p.m. but it would be of infinite length. The period of time that your polar sundial will indicate depends upon how long you want to make it.
Congratulations! Your sundial is now ready to use. All you need to do is find a sunny spot and find the direction of true north, that is the celestial pole. Make sure that your sundial is tilted so the gnomon is pointing to the celestial pole. To find true north please go to "Finding True North" at The Sundial Primer.