The
Sundial Primercreated by Carl Sabanski |

Altitude lines trace the angular distance of the sun above the horizon. Determining the altitude lines for a horizontal sundial is not difficult. Any given altitude will be represented by a circle centered at a point on the dial plate directly below the nodus. In Figure 1 this is the point below the tip of the style. The radius of an altitude line is: Radius = Gnomon Height / tan (Sun's Altitude) The radius is the "Shadow Length" as shown in Figure 1.
The maximum altitude that the sun can reach at any given latitude is determined as follows: Maximum
Altitude = 90° + 23.44° - Latitude The following figures show various dials with the altitude lines included for a common nodus height. The layout of the altitude lines will be affected by the height of the nodus.
As can be seen, the altitude lines for a horizontal dial are concentric circles. They are shown at 5° intervals from 10° to 60°. From this figure you can see how the method of equal altitudes can be used to determine the direction of true north. This technique is discussed on the page "Finding True North".
For a vertical sundial the altitude
lines are quite different. They are shown at 5° intervals from 0° to
60°. |