Most of us usually think of a sundial as a flat disk with an arm that extends at an angle from the center, but actually there are several categories of sundials. Some, like the ones with which we are most familiar, use the edge or tip of a shadow to indicate the time, while others use a spot of light or a line of light. The shadow-casting part of the sundial is called the gnomon which usually is a thin rod or a triangular shaped object with sharp tip or a straight edge.
Sundials can also be categorized by the type of gnomon used. Some gnomons are stationary while others are moveable so that they can be adjusted for the seasons. Gnomons can be oriented horizontally, vertically, in alignment with the earth’s axis or in a direction which was determined mathematically.
Another categorization of sundials has to do with the different types of surfaces that are used on which the spot of light, the line of light, the shadow tip or the shadow edge are cast. The most common surface is the plane – usually in the shape of a disk, however, some other shapes that have been used for sundials include cones, cylinders, and partial spheres. These, as well as more complex shapes, are used for increased accuracy and also for their artistic appeal.
Sundials can be categorized according to how difficult they are to orient. Some sundials require that the installer know the local latitude, the direction of true North, and a very accurate vertical direction. Other sundials are virtually self-aligning and do not require knowledge of latitude etc. The sundial, no matter how it is categorized, is an intriguing instrument that measures time by the position of the sun.
Tags: sundial, sundials, garden sundial, brass sundials, bronze sundial, garden sundials
