Introduction: One of astronomy’s first tools to measure the flow of time, a sundial is
simply a stick that casts a shadow on a face marked with units of time.
As Earth spins, the shadow sweeps across the face. There are many
types of sundials; an equatorial sundial is easy to make and teaches fundamental
astronomical concepts. The face of the sundial represents the
plane of Earth’s equator, and the stick represents Earth’s spin axis.McDonald Observator
