« How the Complication Works »
A moon phase display is one of the so-called minor complications. For watchmakers, it poses less of a challenge than the grand complications – the minute repeater, perpetual calendar, and tourbillon – but it has the advantage of always being visible at a glance. In today's magazine article, we explain how it works and introduce our readers to a selection of watches with a moon phase display.
The Moon – Earth's Fascinating Companion
The moon and its changing phases have fascinated people since time immemorial. Archaeological finds show that the lunar cycle served as the basis for calendars even in early cultures. Because the rhythm of the solar year is what matters for agriculture, however, purely lunar calendars based solely on observing the moon were increasingly displaced by other calendar systems as early as the transition to farming in the Neolithic period. They were replaced either by lunisolar calendars, which are also based on the lunar cycle but are brought at least roughly into line with the solar year through occasional leap months, or by solar calendars, which follow the course of the sun alone.
With the Gregorian calendar, a solar calendar has now become the international standard. In some contexts, however – in Judaism and Islam, for example – lunisolar and lunar calendars are still used, for instance to determine the dates of certain religious holidays or periods of fasting. Since the moon also plays an important role in other areas, such as mythology and astrology, the idea of integrating a moon phase display into mechanical clocks and watches emerged early on.
Moon Phases – Technically Feasible in Timepieces Since the 16th Century
As early as the beginning of the 16th century, clockmakers were able to build wall clocks that could display the current phase of the moon.
The complication was later used in wristwatches as well, but it lost much of its significance during the quartz crisis of the 1970s and with the rise of digital watches. The tide only began to turn in 1983, after Blancpain launched its Caliber 6395, equipped with a moon phase display. This mechanical watch became a remarkable commercial success for the brand, prompting other watchmakers to launch their own models with this astronomical complication.
If you are looking for a moon phase watch today, you will find options in almost every price range. The mechanism behind a moon phase display is relatively simple, so even common base calibers can be fitted with one at comparatively little effort. The differences in quality are considerable, however, and the accuracy of particularly inexpensive models often leaves much to be desired.
Duration and Accuracy of the Display
Astronomically speaking, a lunar cycle lasts exactly 29 days, twelve hours, 44 minutes, and 2.9 seconds. In the classic construction of a watch, however, this is usually rounded to 29.5 days. Because half days cannot easily be "translated" into a gear-based mechanism, a wheel with 59 teeth is generally used in practice, covering two consecutive cycles of 29.5 days each. The display relies on a so-called moon disc, only a section of which is visible at any time through an aperture in the dial.
The disc bears two opposing images of the moon, only one of which ever appears – fully or partially – in the aperture. To display the moon phase correctly, the disc is advanced by one tooth once a day, usually at midnight. However, such a moon phase display has a built-in systematic error that adds up to a difference of around eight hours from the moon's actual position over the course of a year. Within three years, this already amounts to a deviation of a full day. For this reason, correction mechanisms are often built in that allow the moon phase display to be readjusted using a pusher.
Ambitious manufactures in the luxury segment, however, make a point of developing more precise mechanisms from the outset.
The best moon phase mechanisms are so accurate that a one-day correction would only be necessary after more than 100 years of operation.
Moon Phase Watches – Selected Models from Renowned Luxury Watchmakers
Blancpain
A look at selected models from renowned luxury watchmakers shows the wide range of design possibilities for moon phase displays. The Blancpain manufacture, whose name is inextricably linked with the revival of the moon phase display in the 1980s, still offers several models with this complication today, for example in its two collections Leman and Villeret. The Leman models are not merely moon phase watches but highly complex women's and men's watches that also feature a perpetual calendar with pointer date, day-of-the-week and month displays, and a small seconds.
The various versions of the Blancpain Villeret offer almost the same functions, except that they have a central seconds hand instead of a small seconds. In each case, the moon phase aperture is positioned just above 6 o'clock and, on the Leman, combined with the small seconds.
Chopard
With its Chopard LUC Lunar Big Date, Chopard also offers an exclusive moon phase watch. Its self-winding movement is certified as a chronometer and is so accurate that the moon phase display would deviate from the actual lunar cycle by one day only after 122 years.
On this model, the lower half of the dial features two subdials. On the left, between 7 and 8 o'clock, is the moon phase display – which, incidentally, on the Chopard LUC Lunar Big Date can be used for both the Northern and Southern Hemispheres – while the small seconds sits on the right, between 4 and 5 o'clock.
The upper half of the dial, by contrast, is reserved for the panoramic date that gave the model its name.
Omega
The Omega Speedmaster Moonwatch, originally developed as a sporty chronograph for racing drivers and pilots and chosen by NASA as the official astronaut watch, is now also available in a version that carries Earth's satellite not only in its name but also on its dial.
What stands out is the exceptionally detailed and lifelike depiction of the moon. In the aperture on the dial of the Omega Speedmaster Moonwatch Moonphase, it appears not as a graphic illustration but as a high-resolution, extremely detailed black-and-white photograph, and looks surprisingly real.
Hublot and Junghans – Design Opposites Among Moon Phase Watches
If you are looking for a somewhat bolder, more unconventional moon phase watch, the Hublot Spirit of Big Bang Moonphase is one example. Like most Hublot watches, the model with its tonneau case is a striking eye-catcher. Unlike other moon phase watches, the moon disc of the Hublot Spirit of Big Bang Moonphase is not hidden except for the current section; instead, it is merely covered by a disc of semi-transparent quartz whose color varies by version.
The maximum visual contrast to Hublot's opulent moon phase watch is the Junghans Meister Kalender, which by comparison is almost radically understated. It also displays the current position of the moon without departing in the slightest from the sober, elegant style typical of the entire Meister collection.
Between the understated Junghans Meister Kalender and the extravagant Hublot Spirit of Big Bang Moonphase lies a whole range of other luxury moon phase watches, some with a more classic design, others with a somewhat sportier look.
Examples – with no claim whatsoever to completeness – include models such as the Breguet Classique Moonphase, the Union Glashütte Belisar Chronograph Moon Phase, and the moon phase versions of the Longines Master Collection Retrograde, the Longines Conquest Gents Automatic, the Rolex Cellini, and Oris's two collections Artix and Big Crown.
