Functions & Techniques: The Moonphase Indication

The moonphase complication (or moon phase, depending on who/what you’re reading on any given day) is an interesting one to dig into when it comes to watchmaking complications. On one hand, it’s one of the oldest complications in the world of watchmaking, and one that’ll put a smile on just about every watch enthusiast’s face. On the other, it’s absolutely useless. Let’s be real for a moment. When was the last time that anything in your life was/would be/could have been impacted by the current status of the moon’s various phases? No, trivia night doesn’t count. Perhaps for the most superstitious of us, being aware of the occurrence of a full moon, but more than anything it’s just that trivial bit of knowledge that helps fill up a watch dial with something a touch more artistic and abstract.

When we talk about the age of the complication, it’s an interesting one. Based on current information, technically the first moonphase complication pre-dates watchmaking as we know it. Enter the Antikythera mechanism—a device that’s over 2,000 years old, which was uncovered in part of an ancient Greek shipwreck in 1901. Since then, more and more pieces have been lifted from the water, and as best as can be deciphered, the mechanism was used to both track and calculate the future relative position of the various planets, as well as the moon. While not the sexy “the first moonphase came in the ref. XXX Vacheron from 18xx” that some may have hoped for, we can’t be all that surprised. The moon has held cultural significance around the globe, dating back as far as written history and archaeological site research can take us.

The time indication is so prevalent that it remains challenging to pin down the “who came first” with any sort of precision, so we’re not going to split hairs on that matter. Instead focusing on something more useful, we can take a brief moment to explain the mechanics behind it—those are relatively simple. A complete lunar cycle is 29.5 days, when we round things out, though to be precise you’re actually looking at 29 days, 12 hours and 44 minutes, or 29.53 days. This is where the accuracy game comes into play.

In its simplest form, watchmakers would affix a disc to a 59-tooth driving wheel, which would click forward once per 24h cycle. The disc would have two moons on it, and thus halfway around each rotation the disc would center on an open space, or a new moon. Due to the aforementioned gap in accuracy, these watches would fall out of sync with the moon a little over two years and 7 months from being set. As time has gone on, more refinements have come, including the frequent use of a 135-tooth driving disc. Not one to do math in public, I’m not going to calculate the specifics as to how, but this change allows many modern moonphase indications to remain accurate for 122 years—a significant leap over their less refined counterparts. At the end of the day, that’s really all there is to it. Tweak the gearing and make it more accurate. No complex clutch systems, separate balance wheels, or other intricate work that we see in other complications.

Where the game varies most here is in the visual execution, as you’ll see below. Some moonphase indications are larger than others. Some use technology to create a more accurate depiction of the moon. Others use more traditional techniques to create a more artsy interpretation. Regardless of your individual tastes, there’s a moonphase out there that’ll grab your attention one way or another.

De Bethune DB25 Starry Sky Moon Phase

There’s no denying that I have a soft spot for all things De Bethune, and even though they’re not especially known for their moonphase complications, it’s something they execute beautifully. Using a three-dimensional polished sphere, the DB25 breaks away from the standard convention of moonphase indication. This particular version that places the moon against a star-filled sky, paints an artistic picture that’s easy to fall in love with, all while being powered by one of the brand’s elegantly finished calibers. The manually wound white gold piece measures 44mm across, though with short lugs, it wears a bit smaller than one would expect.

F.P. Journe Octa Lune

From a modern indie to a much more traditional one, the Octa Lune offers the same special scarcity as the De Bethune in a completely different execution. Its engine turned dial displays simple indications for time and power reserve alongside a traditional moonphase disc. In the case of this example, a rose gold moon is used to match its rose gold case. This isn’t where the gold glory stops; flip its case over and you’ll see that this Octa Lune’s automatic movement is made entirely of rose gold as well.

Omega Speedmaster Moonphase Chronograph

In the case of this Omega Speedmaster, the execution of its moonphase sort of splits the line between classic and modern interpretation. Yes, the mechanism is traditional, however given Omega’s ties to the moon the brand has opted for a photo-accurate depiction of it rather than a more whimsical one. These Speedmasters are a nice change of pace from the classic Moonwatch we all know and love, and though the piece has always been meant to be more of a tool watch, the complication fits in perfectly.

Moser & Cie Endeavour Perpetual Moon

 As you may recall from our recent coverage of Moser’s Concept dial watches, the Endeavour Perpetual Moon is immediately recognizable as a Moser creation regardless of being devoid of branding on its dial. The plain-jane execution simply allows its moonphase complication to sing, and the way the complication comes together in these references is done in its own unique way. Rather than a dial aperture where the moon on a disc cycles in and out of view, the moon of the Moser remains still, and the shadow to mask the moon tracks across. This allows for a larger display that instantly stands out from the pack.

Jaeger-LeCoultre Master Perpetual Calendar

Before we finish this list, a classic perpetual calendar had to make the cut. The JLC Master Perpetual Calendar may not be as highly sought after as some of those from Patek, Lange, or others, but the value proposition of this perpetual calendar is pretty much unrivaled in the category. The slender 37mm gem may not be a record-breaking ultrathin, but its proportions are spot on for a classic dress watch. Speaking to its moonphase complication, in this steel execution with a black dial, the gold and blue moonphase stands out in just the right way.

Harry Winston Excenter Bi-Retro Perpetual Calendar

 OK, maybe a second perpetual calendar is in order, but something far more out of the ordinary? Enter Harry Winston. Lurking inside its peculiar case design we have a unique perpetual calendar indication with retrograde displays for both the month and the date, accompanied by an off-center time indication and moonphase complemented by a star-filled surround. The movement also has a GMT hand displaying a second time zone, which is an interesting and tricky addition to the caliber. Fun fact, this caliber was developed by Jean-Marc Wiederrecht (now of Agenhor), who is the mastermind behind the recent Agengraphe caliber that powers the Moser Streamliner chronograph and the Singer Track 1.