A moonphase complication is poetic as much as it is technical. It’s a complication like no other, depicting the current phase of the moon as seen in the sky, graphically on the dial. Unlike the time or date that is shown by numerals or indices, this one shows an actual resemblance of the moon.
If you delve into the history of moon-phase complications, it points to the history of time itself. Back in the days, moonphase complications were used by travellers to know more about full moon days, so they could plan their travels accordingly. The second theory suggests that moon phases were directly linked to the tides which allowed travellers to determine whether it was safe to cross a coastal stream. Our concept of time as divided into a year and 12 months is borrowed heavily from the moon. The lunar calendar has influenced the notion of time, by depicting the length of a month by the time between two full moons. As civilization progressed, moonphase indicators were found in clocks and it was just a matter of time before they made their way into wrist watches.
The inner workings of a moonphase
The technicalities of constructing a moonphase are also interesting. The movement of the moon around the earth is pretty regular and this is the basis of the complication. The moon takes 29.5 days to complete one cycle which is depicted through the two rotating discs. A conventional moonphase mechanism consists of a 30-toothed disc. The disc has two gold or silver coloured moons that sit opposite each other on a blue background (Usually Blue). The waxing and waning of the moon are depicted by curved apertures in the dial. When the moon is centred in the window, it indicates a full moon. When no part of the moon appears, this indicates a new moon. The disc continues to travel clockwise or anti-clockwise.
The question of accuracy is also relevant here. While the cycle of the moon is relatively accurate, it is not completely accurate and there is a difference of about point zero three days a month between the actual and measured lunar cycle. While this may not really seem much (for the wearer that is) the watch industry thrives on accuracy and there are other mechanisms to take care of this difference as well.
Today, a moonphase complication is probably one of the most well-loved complications by men and women alike. The movements of the moon reflected on the watch again take you on a journey…either to a nostalgic magic past when time began, or in the realm of poetry and beauty, which can only be experienced.