Complications: Moonphase

A complication is usually defined as any information displayed on a watch over and above simply telling the time in hours, minutes, and seconds. Many complications, such as a date, GMT or chronograph, display information that can be heavily relied on, and the requirements for choosing a watch in which they are featured are often legitimate and unemotional ones. The same cannot ordinarily be said when it comes to the moonphase.

Frederique Constant Classic Moonphase

Mankind has been tracking the cycles of the moon for tens of thousands of years. In those earliest times, a small stone inscribed with a lunar calendar would have been carried on long hunting trips or during seasonal migrations where planning around nocturnal light or temperature variations was vital. The obvious question, and it’s one that I don’t have the answer to, is why does the complication remain so popular today, other than it being an elegant representation of the passage of time.

Early Adoption

Astronomical clocks such as the famous Prague Orloj have included a display of the relative position of the moon since the 14th century, and it’s possible even they can trace their origins back to the Antikythera mechanism from ancient Greece, which included the moon phase, calendar cycles and eclipses among its displays.While no longer useful in everyday life, the romanticism of the moonphase made its way from more complicated and elaborate clocks to pocket watches and then on to similar wristwatches, often as part of a perpetual calendar display. The first perpetual calendar wristwatch was produced by Patek Philippe in the 1920s using a movement originally designed for use in a pendant watch made decades earlier. Breguet soon followed, and the popularity of the complication grew into the 1930s and ’40s.


In Pursuit of Accuracy

Early moonphase mechanisms and a large segment of entry-level executions we see today record the phase of the moon through the use of a 59-tooth wheel advancing one notch every 24 hours. That wheel is linked to a disc with two moons displayed on it so that one full “phase” takes 29-and-a-half days. Now, the actual average duration for the Moon’s orbit around the Earth, known otherwise as the synodic month, is 29 days, 12 hours, 44 minutes, and 2.8 seconds. One of the more widely seen calibers, the ETA/Valjoux 7751, uses this exact setup. Although 29-and-a-half days is fairly accurate for a single extra wheel, it would be a day out every two years and seven months. For most people and most watches, this should be an acceptable level of accuracy given the number of instances the watch is likely to run down and require resetting in that time, or the frequency with which the wearer is probably happy to calibrate the time. Watchmakers, however, aren’t a breed to rest on their laurels when it comes to accuracy.

By swapping out the 59-tooth wheel and replacing it with a combination of a seven-point start wheel attached to a 16-tooth gear that meshes with another 135-tooth gear, the accuracy can be vastly improved to only one day out of every 122 years. As the seven-point star moves one notch per day, the 16-tooth gear moves 16/7 (= 2.2857) notches and the adjoining 135-tooth gear rotates by the same number. To make a full revolution of all 135 notches, this gear would need to be acted upon 135/2.2857, or 59.0625 times. Sharing the same characteristic of having two moons printed on the disc, each one completes its “phase” in 29 days, 12 hours, and 45 minutes. Much better!

Ochs un Junior’s unique moonphase wristwatch.

For most watchmakers, this is as far as they have deemed it necessary to go. However, Ochs und Junior have created an amazing five-gear system running on top of an ETA 2824-2 that lengthens the accuracy period to over 3,000 years!

Then there’s Christiaan van der Klaauw, who began as a maker of astronomical clocks and only later began producing wristwatches with astronomical complications. The Real Moon Joure not only features a three-dimensional moonphase display—with one-half of the moon painted silver and one-half painted black—but it also boasts accuracy of one day per 11,000 years. The watch has two barrels, giving it a power reserve of 72 hours (thankfully each purchase comes with a winder). If 11,000 years still isn’t enough, Andreas Strehler produced the Sauterelle a Lune Perpetuelle 2M in 2014, which only deviates by a single day in over two million years—truly an amazing feat of engineering.

In Pursuit of Beauty

The other side of the complication is about beauty, and that is probably the reason watch lovers adore moonphases even today. As the decades have gone by, the moon itself has been commonly depicted by a cherub-like smile, a winking face, a solid silver disc, and more recently a photo-realistic cratered moon. Although the classical depiction of a silver or yellow moon crossing a starry sky remains the most common, there are plenty of interesting and unusual arrangements available today.

Omega Speedmaster Moonphase Co-Axial Master Chronometer with a photo-realistic moon.

In terms of beauty, Arnold & Son set the bar high with the HM Perpetual Moon, which features a highly detailed sculpted moon circling the dial. The moon itself is 11mm in diameter and extends over most of the upper half of the dial. If the Arnold & Son is over budget at a snip under $30,000, the Christopher Ward C1 Grand Malvern Moonphase offers a similar aesthetic for a fraction of the price. The detailing on the moon may not be quite as captivating, but at $1,595 and a moonphase deviation of one day per 128 years thanks to the Calibre JJ04 beating inside, the Christopher Ward offers a great value alternative.Also depicting the moon with plenty of detail, the Omega Speedmaster Moonphase Master Chronometer Chronograph contains a fun easter egg—an imprint on the moon of Neil Armstrong’s footprint, a nod to the Speedmaster’s heritage.

Sinn’s recently announced 3006 Hunting Watch shows off a lumed moonphase display in keeping with its intended night-time usage, but this isn’t something new. The Ball Trainmaster Moonphase features a lumed, textured moon aperture with a black disc slowly rotating and displaying the waxing and waning phases against a static moon.

One of my favorite depictions of the moon is featured on the creations of Stepan Sarpaneva. A dark and brooding moon face is visible through the dial aperture of the Korona K0 and sits beneath a dial that invokes thoughts of industrial structure and the natural phenomenon of the northern lights at the same time.

For such a simple and largely superfluous complication, there are more than enough variations in both mechanism and design to keep the romance of the moonphase alive and well.

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Brad stumbled into the watch world in 2011 and has been falling down the rabbit hole ever since. Based in London, Brad's interests lie in anything that ticks, sweeps or hums and is slightly off the beaten track.