watchionary

A moonphase watch shows the illuminated portion of the moon as seen from Earth at any given time during each lunar month, which lasts for 29.5 days. That is how long it takes to move from an invisible new moon to a full moon and back again. When the moon is waxing or declining, the moonphase is visible via a crescent-shaped aperture. A moonphase watch with two twin moons perched on a disc underneath the watch face is called a ‘bosom’ moonphase watch.