…of time and the Sun

On the floor of my office at Haverford College there is painted in several colors a precision sun dial which, after the manner of Topsy, “just growed”. It all started in a casual way, but as it has developed for more than two years, it has become increasingly interesting. From it, my students and I have learned much about the equation of time and the need for the mean solar second. The inappropriateness of the sun as a primary time keeper, despite our constant dependence on its regularity, is clearly disclosed. The method of approach has been that of the natural philosopher who seeks a more complete understanding of the sun’s slightly irregular apparent motions. The tools employed are mostly those that have been available through the centuries. With the exception of a pocket watch or an electric clock frequently checked against time signals from the Bureau of Standards’ Station WWV, the tools are like those available to the ancient Egyptians or Mayas, and they compete in accuracy with those used by Tycho Brahe.