A moon-phase watch, also known as a lunar watch, is a type of watch that displays the phases of the moon. This is achieved through the use of a small aperture or window on the watch face, which shows a portion of the moon as it appears in the sky.
A moon-phase watch typically has a small disc with two identical moons on it, which rotate behind the aperture as time passes. The disc is calibrated to represent the 29.5-day lunar cycle, which is the time it takes for the moon to go from a new moon to a full moon and back to a new moon again.
Moon-phase watches are popular among collectors and watch enthusiasts for their unique and sophisticated design. They are often seen as a symbol of elegance and refinement, and are frequently used for dress watches or other formal occasions.
In addition to their aesthetic appeal, moon-phase watches can also have practical uses, particularly for those who spend a lot of time outdoors or who engage in activities such as hunting or fishing, where knowledge of the lunar cycle can be useful for determining the best times to pursue these activities.