What Is a Moonphase Watch and Why You Should Own One

If you want to know all about what a moonphase watch is, you’ve come to the right place!

Ah, the moonphase watch. Few complications are so particular yet so well-loved. Think about it. It’s about as quirky or unconventional as a music-box-esque singing bird complication or a declutchable rotor. A moonphase is as romantic as the former and as sciencey as the latter. 

Yet, no one would look at a moonphase watch and think it’s as weird as either. It’s one of the few kinds of complications that actually sit well on a dress watch dial, too.

Dress watch lovers aside, it’s a complication that’s captivated enthusiasts of watch mechanics, horological history, as well as both the romantic school of style and the sporty set. 

Have you ever wondered why this is? Heck, have you ever wondered what a moonphase watch is in general?

Here’s everything you need to know.

The Moonphase Complication: What Is It Exactly?

A moonphase watch is one that features a moonphase complication. Through an aperture on the watch dial, you can see the different phases of the moon. Originally astronomers and sailors used this feature.

Remember, we’re able to see the moon because the sun lights it up by reflecting off of its surface. Depending on where the sun and moon are at a given time, you can see portions of the moon.

If you look in the moonphase aperture on a timepiece, you’ll see one of four displays:

• A new moon. This means the moon is in between the sun and the Earth, so you see nothing.
• A half moon (right side). Now, the moon has traveled a quarter of the way around Earth. It’s at a right angle from the sun, and its right half is lit up.
• A full moon. The moon is now 180 degrees away from the sun and is fully illuminated.
• A half moon (left side). The opposite of the right-side half moon. This means the left is lit up.

The moon phase displays usually feature two circles representing the moon, “lit up” in accordance with the current phase. The designs range, falling anywhere on the symbolism-realism spectrum, with different degrees of details and applications.

They can be powered by a mechanical movement, or they could be a quartz moon phase indicator.

And in case you forgot, the lunar cycles are a month-long — or 29.5 days, to be exact!

The Bosom Moonphase Watch

There are two kinds of moonphase watches. The bosom design is one in which the aperture is shaped like a semicircle.

The bottom of the semicircle, the part that would usually be a straight line, is often carved out to look like two or three circles, representing the earth (though I think it looks more like clouds).

This is the most common design.

The Radial Moonphase Watch

A radial moonphase is one that features a subdial — the hands-on subdial points to images of the different phases of the moon.

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So, unlike the more common bosom version, the moon symbols aren’t the elements doing the moving.

A Brief History of the Moonphase

The moonphase complication has actually been around long before wristwatches were even commonly worn. Pre-cursors even existed in ancient Greece, with the world’s first computing machine, the Antikythera, from around 178 BC.

In the 1500s, an inaccurate version of the moonphase complication was built into astronomical church clocks (remember that many people thought the Earth was the center of the universe at the time). In the 16th century, grandfather clocks often depicted moon phases. 

Not only did astronomers need to know the phases of the moon, but so did sailors — and so do astronomers and sailors to this very day. After all, the phases of the moon affect the ocean tides.

So, this complication was eventually incorporated into pocket watches. In the 19th century, affordable pocket watches became more available, thus becoming an important tool for ocean goers.

Then, in the 20th century, the moonphase appeared on wristwatches. Patek Philippe, a brand still associated with this complication, introduced the first in 1925. Some may argue that if it weren’t for the moonphase, there wouldn’t be a perpetual calendar, which is also an astronomical measurement.

How Does a Moonphase Watch Work

So, here’s how the phases of the moon are represented on a moonphase complication.

Behind the aperture on the dial is a disc. That disc features two smaller circles. They might be applied discs or embossings, or even painted-on circles. Either way, they’re designed to be two identical moons.

The disc rotates per the moon’s cycle, meaning it fully circles back in 29.5 days. 

For mechanical watches, which include automatic ones, a gear moves a disc. This gear has a whole 59 teeth on it, which makes the movement subtle. 

This is how you’re able to get an entire month’s worth of a cycle represented on a small disc. To be exact, every two teeth on the gear represents one day, making the movements ever so slight.

With quartz watches, the moonphase complication is usually automatically programmed in since they’re battery-powered. And just like when comparing mechanicals and automatics to quartz watches, the quartz moonphase timepieces tend to be more accurate.

Setting Your Mechanical Moonphase Watch

Some watches are more complex than others. However, for a basic mechanical moonphase watch, you’ll often set it as such:

First, it’s advisable to pull out the crown and set the hands to 6:30. For most watch movements, there’s a “danger zone.” This means that when you’re setting any complication, including a date, it can damage mechanisms in the movement. By setting your hands to 6:30, you’re in the safe zone in basically any caliber.

Then, find out what phase of the moon we’re currently at and whether it’s waxing or waning. The internet can help with this.

Next, move the disc to the full moon position. From there, figure out how many days it’s been since the last full moon.

Now twist the crown, usually one notch per day, until you get to today’s current phase of the moon. Now push the crown back in, and you’re good to go!

FAQs

Do you still have questions about moonphase watches? Here are some common ones.

What Is the Point of a Moonphase Watch?

It was originally used by astronomers as well as sailors who needed to know the phases of the moon because it affected the tides of the ocean.

Are Moonphase Watches Worth It?

They come in a wide range of prices. If you want a Moonphase watch, you can likely find one that’s worth it for you.

Why Are Moonphase Watches So Expensive?

Many mechanical moonphase watches are expensive because it’s a complex complication to build. However, as mentioned, there are quartz versions at much lower prices these days.

Conclusion: A Watch for All Seasons and Phases

Again, theMoonphasee watch really does have a big audience, despite how non-standard it is.

It’s elegant enough for dress-watch fans but has a romantic quirkiness for those who like something unique. Meanwhile, it’s still sciencey enough for the gadget lovers who love slide rules and chronographs.

And these days, they come in such a wide range of styles and prices.

What’s your favorite moonphase watch? Leave a comment and let me know!