Sundials are ancient pieces used to tell time by referencing the shadow cast by the sun. Sun dials consist of a thin rod or gnomon and a flat surface usually etched with numbers. The gnomon casts a shadow on the number markings depicting time. From an astronomical clock, the sun dial has evolved into a compass and now, a favorite garden or yard fixture. As pieces of history, sundials add a classy vibe in gardens, yards, or outdoor spaces.