A disc, decorated with golden stars and two golden moons against a blue or white background representing the moon, rotates within an aperture. The disc is cut from a wafer of corundum crystal (sapphire).

Gold was condensed onto the disc by means of a vacuum process through a photographic mask to create the shape of the moons and stars. The aperture is cut at its upper edge in order to represent the lunar cycle.

During the first days of each lunation, the leading edge of a golden moon becomes visible as a crescent on the left of the aperture and appears to wax as it emerges beyond the curved edge of the aperture representing the lunar terminator.

Half way through the lunation, the moon appears full. It then wanes as it disappears behind the terminator on the right of the aperture. As the moon vanishes, the second moon on the disc is ready to appear on the left.