Sundials and shadow clocks were being used ... but another kind of clock! Clepsydras, or water clocks, tracked the passage of time by regulating the flow of water from one vessel to another.

We've come a long way from sundials for telling the time ... Look for outdoor clocks that are labeled as water-resistant. If ...

Julien Coyne invented a digital sundial. Sundials usually cast a line or triangle to indicate the hour. This one is designed so that when light passes through, it displays the shapes of numbers.