Moonphase Watches

The Moon has held us spellbound for millennia and continues to be an object of fascination, even now that science—helped by NASA’s moon landings and subsequent lunar research—has helped demystify it.

For ancient civilizations the Moon was commonly a symbol of fertility, but lunar cycles were also observed for practical reasons since they indicated the passing of days, months, seasons and years. By tracking the cycle of the Moon, our ancestors were able to conceive the first primitive lunar calendars, with the first astronomical “computer”—the Antikythera Mechanism—emerging in Greece in the second century BC.

The earliest known moonphase indicators appeared on 14th-century clocks, in particular ones that adorned the towers of cathedrals and town squares, enabling local residents to observe them with ease. However, it wasn't until the 17th century that the moonphase complication as we know it today found its way into pocket watches.

Christiaan Huygens, a Dutch astronomer and mathematician, was instrumental in developing moonphase complications in a clock, devising a mechanism that accurately depicted the moon's phases. This major breakthrough in 1675 allowed for the eventual miniaturization of moonphase displays, making them suitable for inclusion in portable pocket watches. In the days before electricity, these were especially useful to long-distance travellers and coachmen who depended on the light of a full moon for nocturnal journeys.

The golden age of moonphase watches occurred during the 19th century when pioneering watchmakers like the great Abraham-Louis Breguet created timepieces that blended technical innovation with aesthetic elegance. Breguet's work laid the foundation for the moonphase complications that would become a staple in luxury watchmaking.

By the early 20th century, wristwatches were outselling pocket watches, and moonphase indicators were being incorporated into the finest models money could buy. Watchmakers such as Patek Philippe—who were the first to put this complication in a wristwatch in 1925— Universal Geneve Audemars Piguet and Breitling all entered the game.

By the time of the quartz revolution in the latter half of the 20th century, the mechanical moonphase complication, as with so many complications, became an anachronism. Yet it remained a hallmark of exclusivity and craftsmanship, the intricate gears and wheels required for accurate moonphase displays posing too great a challenge for cheap mass production.

These days the romance of moonphase watches continues to captivate watch lovers. Modern advancements in horology have allowed for even more precise and detailed depictions of lunar cycles. And high-end watchmakers are increasingly replacing the conventional crescent-shaped moonphase aperture—typically featuring a painted moon and stars—with more creative renditions of our satellite. These include three-dimensional displays or even discs made from genuine slivers of meteorite—enhancing the watch’s celestial appeal.

A moonphase indicator on a watch typically comprises a crescent-shaped aperture on the dial which partially reveals a rotating disc beneath. On this disc is a full Moon—often in gold and accompanied by a scattering of stars for aesthetic effect—which “waxes and wanes” as it passes along the curved aperture. These cyclical progressions represent the four main phases of the moon as seen from Earth.

These four main phases are: the new Moon, when the Sun and Moon are aligned and the Moon cannot be viewed from Earth; the first quarter, when the Sun hits the right half of the moon; the full Moon, when all of the facing surface is illuminated; and the third quarter when only the left half of the moon is on view.

In terms of the movement, the rotating disc itself is controlled by a 59-tooth driving wheel, which uses a finger attached to the hour wheel to advance the disc one notch every 24 hours. When a lunar cycle is complete, a second Moon on the disc moves into view and the process starts again. Why a 59-tooth driving wheel? That’s because a lunar cycle lasts 29.5 days and there are two moons on the disc (29.5 x 2 = 59).

The moonphase isn’t horology’s most accurate complication. Basic models will need occasional correction, just like any mechanical watch. But there are high-end models with specially calculated movements capable of delivering an accurate moonphase to the nearest day for hundreds of years or more. And anyhow, accuracy matters little for most moonphase devotees. Above all a moonphase watch serves as a reminder of our deep attachment to Earth’s only satellite, and to our distant ancestors who depended on it so much.

A moonphase display can be incorporated into watches at the highest end of the price spectrum but can just as often be found in watches at more accessible price points. You can find great entry-level moonphase watches from brands such as Baume & Mercier and Longines. Among the elite brands, several iconic Patek Philippe watches feature a moonphase display, with the contemporary Sky Moon tourbillon and the vintage reference 1518 the most revered, while A. Lange & Sohne’s 1815 Moonphase is considered a masterpiece. Sought-after vintage moonphase watches from Rolex include the reference 6062, produced in tiny numbers in the early 1950s, and the even earlier 8171.