What is a moon phase dial?

A moon phase dial is a specialised horological display that tracks the lunar cycle using a rotating painted disc. It reveals the waxing and waning of the moon behind a curved aperture on the clock face. These mechanisms were integrated into tall case clocks and select table pieces, combining practical timekeeping with astronomical illustration.

How does a rolling moon work?

The rolling moon mechanism uses a gear train connected to the primary clock movement to rotate a disc carrying two painted moons. The disc completes one full revolution every fifty-nine days, showing each phase consecutively. This gearing requires manual adjustment only during months with fewer than thirty-one days or when the clock has stopped running.

How do I set a moon phase dial?

Setting the moon roller generally involves using a small finger or a designated pusher to advance the disc until it matches the current night sky. Reference an almanac to confirm the exact lunar phase before making adjustments. Care must be taken not to force the mechanism while the internal automatic calendar teeth are engaging near midnight.