How Does a Moon Phase Watch Work | A Thorough Guidelines

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Moon phase complication in a watch was one of the first complications that were introduced in a wristwatch. It looks cool and it represents the magic of mechanics. In the past, moon phase watches were used for practical reasons in which it was necessary to know the current phase of the moon but nowadays it is just mechanical magic to make the watch look stylish.

Undoubtedly the Moon phase indicator in a watch is one of the coolest features ever invented. However, it works accurately but the mechanism that makes it works is quite complex. Today we will learn how does a Moon phase watch works in detail.

What is a Moon phase watch?

Moon phase watches are those which are capable of repressing the current phase that is on the sky on a watch. So basically you’ll see the phase of the moon on your wristwatch similarly you see on the watch. The natural phenomenon of the moon cycle is being displayed on a watch mechanically.

There can be a disk or sundial on your watch that will represent the moon cycle. Different companies approach in different ways to display the moon phase but all different ways do the same thing. The watches were invented to use for astronomical purposes but nowadays Moon phase watches are produced to show that we can still show the moon cycle on a watch using mechanical parts.

How Does Moon Phase Watch work?

The basic understanding of Moon phase watches’ working process is that the cycle of the moon most commonly represents a crescent-shaped aperture. On that aperture, there is a disk under the dial with two identical moons. The disk is controlled by a 59 driver wheel tooth and the movement uses a mechanical finger that notches the disk one time every day.

The lunar cycle of the moon is 29.5 days. So, when one moon cycle is completed the other moon cycle starts on the disk and that is how the moon cycle is controlled by the 59 drive wheel tooth. Here 29.5*2=59 and that is why we need two moons on the disk. This process is called the “bosom” Moon phase.

Some companies use a different approach called ‘radial’. Here, an indicator hand tracks the lunar cycle of the moon. Though the presentation is different here, the mechanism that drives the cycle is exactly the same.

Why is Moon Phase Addressed as a Complication?

When the timepiece was invented, it was invented to serve the purpose of time-telling. The main job of a wristwatch is telling time and anything that does not relate to telling the time is called a complication.

As the industry grew date and day function was also included in the watches and people accepted it as it helps to know the time, date, and day altogether. But day by day watches started to come with features that people have never imagined. In modern times a smartwatch can do so many things that seemed impossible some years ago. It works like a mini-computer.

But all these features do not help to tell time or anything related to that. As the Moon phase feature in a watch is an extra feature and it is not anything related to time-telling so the Moon phase feature in a watch is called a complication.

OLEVS Automatic Mechanical Moon Phase Wrist Watch

$138.00  in stock
as of May 19, 2022 12:47 am

How Accurate Are Moon Phase Watches?

The Moon phase watches are pretty accurate but Moon phase watches calculate the moon’s lunar cycle in 29.5 days but in reality, it is 29 days, 12 hours, 44 minutes, and 2.8 seconds (29.53 days). The 59drive wheel is highly accurate but it also lacks precision after some time.

In every 2 years, seven and a half months the 59 drive wheel movement loses a full day and you have to manually adjust the watch to keep the right track of the Moon phase. So it is accurate but it needs a little adjustment every three years.

The 59 drive wheel is not the only movement for showing the Moon phase there are some more and the 59 drive wheel is the basic one. Some advanced movements can also be more accurate. These advanced movements can create noticeable differences in inaccuracy.

Some luxury brands use the 135-tooth driving wheel movement in their watches to show the Moon phase. It allows the company to accurately demonstrate the Moon phase on the watch. This 135-tooth driving wheel loses a full day once in 122 years which is significantly better than about 3 years.

Andreas Strehler’s “Lune Exacte ” is the most accurate moon phase watch ever made. This is for those who do not want to sacrifice accuracy for even a bit. This watch loses a full day in two million years.

How to Set a Moon Phase Watch?

There are different types of Moon phase watches with different levels of complexity and the setting process of these watches is also different. Floor these below-mentioned procedures which will work in most of the watches.


Find out how the moon will look tonight from the earth using the internet. There are plenty of websites that will show you the exact result. You do not have to wait till night and manually determine the Moon phase and even if you do it will likely not be so accurate.

Determine whether it is waxing (going from New Moon to Full Moon – left side of the aperture) or waning (Full Moon to New Moon – right side of the aperture).


Now pull the crown of the watch and set the watch time to 6.30 before you start setting the Moon phase. It is nothing but just a precaution so that you do not cause any damage to the watch movement while you are setting the Moon phase.


Now press the corrector on the case side to advance the Moon phase. As you will press the corrector it will advance. Now count how many days it has been since the last full moon or new moon since it is easiest to recognize those faces on the aperture.

So let’s say it’s eight days since the last full moon. Advance the moon phase until it is a full moon and then press the corrector seven more times to account for seven days. Now set the date of the watch one day behind as well set the time making sure to cycle through one whole day to get to the correct day.

You may notice that the date will change at midnight but the Moon phase will change at 1:00 clock. Now, the date is correct, AM/PM correct and so does the Moon phase.

Frequently Asked Question (FAQ)

Which drive wheel does a Moon phase watch uses normally?

The most common drive wheel used in a Moon phase watch is the 59 teeth drive wheel. The drive advances one notch every day to show the current moon phase.

Is the 135 drive wheel more accurate than the 59 tooth drive wheel?

Yes, the 135 tooth drive wheel is way more accurate than the 59 tooth drive wheel. The 59 drive wheel loses a full day in about three years while the 135 drive wheel loses a full day after 122 years.

What are radial Moon phase watches?

The bosom Moon phase watches show the current phase of the moon on a crescent-shaped aperture on the dial. But the radial Moon phase watch indicates the current shape of the moon using an indicator.

What is the real age of the moon?

The actual age of the moon is around 4.5 billion years.

What is the lunar cycle?

The time the moon takes to orbit the earth is known as the lunar cycle. The moon takes 29 days, 12 hours, 44 minutes, and 2.8 seconds (29.53 days) to complete a full cycle.

Final words

The Moon phase complications in a watch were one of the oldest complications introduced in a watch. This complication is pretty accurate and the mechanism it uses is pretty complex to understand.

In this post, I have tried to make you guys understand how does a Moon phase watch works. Hopefully, we have got a pretty good idea of the moon phase watch’s working principle.

As an Amazon Associate, I earn from qualifying purchases.

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