A sundial is essentially a clock. But more specifically it is a clock that uses the position of the sun to indicate the time. Typically a gnomon casts a shadow upon a plane or surface. On this surface are found markings that indicate the time by the position of the shadow.

There are several types of sundials. Each type serves the same purpose: to tell time by the position of the sun. But the method used to extract the data from each sundial is different. The scope of this hand out is not to instruct you in the different types of sundials, or how to use them, but to teach you how to use one type in particular. This type is known as the horizontal sundial. These are, in my opinion, the simplest to setup, and use. To find out about the other types of sundials that are known, I would direct you to one of the books that I have included in the section called Suggested Reading. Any of these books will tell you much more about sundials and their various forms than this hand out. If you are even remotely interested in sundials, I would recommend getting one of these books.