Sundial

time · sun · ancient invention · geometry

Shadow tells time. A sundial has a stick called a gnomon that casts a shadow on a flat plate. As the sun moves across the sky throughout the day, the shadow points to different hour-lines, just like the hands on a clock moving around a clock face.

The style matters most. The most important part is actually the edge of the gnomon called the style, not the thick shadow. This thin line is what points to the exact time on the dial.

Tilted to Earth's angle. For a sundial to work correctly all year long, the style must be tilted at the same angle as your location on Earth. The angle equals your geographical latitude, which is why a sundial in France needs a different tilt than one in Australia.

Many designs possible. Gnomons can be simple rods and wires, or they can be fancy metal castings with beautiful decorations. Different shapes work, and you can make a simple sundial or an elaborate work of art.