Sundials Make Interesting Freshman Design Projects

The design of sundials makes an ideal design project for students enrolled in Intro to Engineering courses for several reasons. First, the task requires some computation, but the level of computation is accessible to any engineering freshman (nothing beyond trigonometry). Second, the project requires the use of simple hand-tools and some simple mechanical design. For example, one may add Vernier scales to the main scales. Third, the project involves some interesting, underlying science that is within the grasp of engineering freshmen. Fourth, there is a wealth of information on the subject on the worldwide web, giving students experience in searching the web for information, and obviating the need for the instructor to provide printed material to the students. There are many sundial types from which to choose (equatorial, horizontal, vertical, and analemmic to name a few) which makes it easier to keep students from "recycling" projects from one semester to the next. Introduction: We shall discuss four different sundials: equatorial, horizontal, vertical, and annalemic. In addition, we discuss finding true north, finding latitude and longitude, sundial corrections and the equation of time. Finally we include a brief discussion of the results of using this material in a section of Fall 01 Intro to Engineering. Equatorial sundials: The equatorial sundial is the simplest of the dials we shall discuss since the hour lines are equiangular. The dial consists of a circle (or semi-circle) with the ends of the hour lines spaced equi-angularly around the circumference. (6 AM and 6 PM fall on the diameter of the circle.) The gnomon consists of a thin rod placed perpendicular to the circle and passing through its center. (See Figure 1.) To use the equatorial dial it is necessary to know the direction of true north (The gnomon must point north.) and the location of the ecliptic. (The plane of the dial must lie in the plane of the ecliptic.)