Complication guide
Moonphase: how the complication works
A moonphase complication shows the current phase of the moon through an aperture, using a disc painted with two moons that rotates under the dial.
The moonphase is one of the oldest decorative complications. A disc painted with two identical moons sits below the dial and turns slowly, so that one moon then the other crosses a shaped aperture, mimicking the moon growing from new to full and back.
A common moonphase disc has fifty-nine teeth and is nudged on one tooth a day, which approximates the roughly twenty-nine-and-a-half-day lunar cycle closely enough that the error is only about a day every couple of years. More elaborate astronomical moonphases use a larger gear count to stay right for a century or more.
Related complications and calibers
ChronographA chronograph is a watch with a built-in stopwatch, started, stopped a
Automatic windingAn automatic, or self-winding, movement winds its own mainspring from
Date and day-dateA date complication shows the calendar date through an aperture; a day
GMT and second time zoneA GMT watch shows a second time zone on an extra hand that circles the
All complications and typesBrowse every guide