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The Encyclopedia of Horology

Pocket watches · Complication

Moon-Phase Pocket Watches

Partially verified

Watches displaying the current phase of the moon, typically through a rotating disc visible in a dial aperture.

Mechanism

A wheel with 59 teeth, advanced by one tooth per day, rotates a disc bearing two moon images so that a full cycle of phases appears roughly every synodic month.

Typical characteristics

  • Painted or engraved moon disc showing two moons
  • Aperture in the dial, often at 6 or 12 o'clock
  • Frequently combined with calendar functions

Identification characteristics

  • Moon aperture and disc visible on the dial
  • Accuracy of the moon-phase train (some approximate, some highly precise) varies by maker

Collector significance

A decorative and astronomical complication frequently paired with calendar work on higher-grade watches.

Known variations

  • Simple moon phase
  • Precision moon phase (long-cycle accuracy)

Diagram

date ring, thirty-one positionsdate aperturedriving wheel and jumper
Schematic: calendar work under the dial. An outline schematic drawn to show the arrangement of the parts discussed here. It is not a dimensioned working drawing and does not depict a particular maker's calibre.

Sources & references

  1. General horological surveys

Where sources disagree, the disagreement is stated rather than resolved silently.