The
Sundial Primercreated by Carl Sabanski |

The polar sundial is universal and can be used at any latitude. The hour lines are parallel to each other and are symmetrical with respect to the noon line. The gnomon is positioned on the noon hour line with its style parallel to the dial plate. The dial plate lies parallel to the Earth's axis, i.e. it is tilted to an angle equal to the latitude where it is located. As the distance to the 6 am and 6 pm hour lines approach infinity, the time that can be indicated by the dial is limited to the practical width of the dial plate. The distance between the hour lines and the sub-style can be calculated as follows. In this case the sub-style is the noon hour-line. If the gnomon has an appreciable thickness, then a noon gap would appear and two sub-styles would exist. By choosing a gnomon height GH: X = GH * tan (h) where h is the hour angle, in degrees, given by: h = (T and T Table 1 list the distance to the hour lines for 15-minute intervals assuming a gnomon height of 1. By selecting a gnomon height you can easily determine the distance to each hour line by using the multipliers. The number of hours displayed can be determined by selecting the dial width. Click here to download a spreadsheet that will perform these calculations for you.
Note that the distance to the 9 am and 3 pm hour lines is equal to the height of the gnomon. As an example, selecting a gnomon height of 2.5 inches will result in a dial width of 37.98 inches for a polar sundial dial that indicates time between 6:30 am and 5:30 pm. Figure 1 illustrates the layout of the hour lines for a polar dial and how it must be installed to function correctly at any latitude.
Rather than using a plate for the gnomon, a vertical rod can be used to create a nodus. It is then possible to show the declination lines on the dial plate. Figure 2 illustrates such an example. The height of the nodus will affect the shadow path throughout the year and the number of hours that can be displayed on a dial plate of a given size.
For an image complete with
shadow click here. |