The
Sundial Primercreated by Carl Sabanski |

Figure 1 illustrates a cross sundial. The sundial is independent of the latitude and can be used anywhere. The top face of the cross faces north and is tilted back toward the south until it lies in the plane of the equator. The angle of the top face to the horizontal is equal to the latitude. The edges that act as the styles will then be parallel to the earth's axis and point to the north celestial pole.
Figure 2 illustrates the layout of the hour lines for the cross sundial. This sundial consists of 5 cubes and each of the 6 dial planes will show 3 hours. An extension of one arm is shown as dashed lines. The hour lines are laid out as for either a polar, vertical direct east or vertical direct west sundial.
The length of the shadow at any hour angle is calculated by taking the tangent of the hour angle. Table 1 provides the shadow lengths for hour angles at 15-minute intervals. As these values are for a cube with an edge length of one unit, the actual shadow lengths are determined by multiplying the actual length of the edge of the cube by each of the values in the table.
For an image complete with
shadow click here. |