The Antikythera mechanism is a 2000-year-old computer for determining the positions of celestial bodies and predicting important events such as eclipses and the dates of the Olympic games. This Demonstration includes only the known mechanism for the Sun and Moon. The additional components needed to display planetary motions are largely unknown. Turning the handle causes a sequence of interlocking gears to rotate, ultimately moving the Sun and Moon pointers around the calendar disc. The phase of the Moon is indicated by a semi-silvered ball, which undergoes one revolution per synodic month. Finally, the back plate features spiral tracks to indicate the date in the Metonic and Saros cycles.