The moon phase complication is one of the most desired complications amongst watch collectors and enthusiasts. What makes it so desirable is not often because of its technical prowess or utility, but because it is so aesthetically pleasing to the eye. Simply put, the moon phase is arguably the most beautiful of watch complications. In this post we will cover this complication and explain what a moon phase watch is.

Man’s Desire for Timekeeping

In the earliest of days of man, time keeping was measured by the Sun, the Moon, and the Stars. A sundial was used to measure the length of the day. As the sun moved across the sky, the shadows would change in direction and length indicating what time of the day it was. Man came up with other inventions to record the passing of time at night, such as the water clock.

Lunisolar calendars were created to keep track of the phases of the moon and the time of the solar year. The months of the calendars were based off the observations of the lunar cycle, with intercalation or embolism being used to bring them into sync with the solar year. In timekeeping, intercalation is an insertion of either a leap day, week, or month into calendar year to allow the calendar to follow the seasons or moon phases.

Moody Moon

The Moon is the easiest astronomical object to observe, needing only a pair of eyes. As it orbits around the Earth, which takes about a month to go all the way around, it is continually changing. It all depends on the angle at which the Sun’s light is beaming on the Moon. There are 8 different phases of the moon.

New Moon:

This phase occurs when the Moon is between the Sun and the Earth. The side that we see from Earth is dark and in a shadow. With the Moon and the Sun being so close to each other, they are above the horizon at the same time, which means they are both in the sky during the daytime. During this phase, we do not see the Moon from Earth.

Also, during this phase, there is the possibility that the Moon will sometimes block out our view of the Sun. This is what is called a Solar Eclipse.

Waxing Crescent:

As the moon continues to orbit counter-clockwise around the Earth, moving east in the sky, the Waxing Crescent phase begins as we start to see a crescent shaped portion of the Moon. This phase typically takes place after a few days of a New Moon.

Like the New Moon phase, this phase also has its own phenomenon known as Earthshine. During earthshine, the Earth’s surface reflects sunlight to the moon, allowing us to see the rest of the moon during this phase.

First Quarter:

During this next phase of the lunar cycle, we can see that half of the Moon is illuminated. At this point, 1/4th of the Lunar Cycle is completed, thus the name First Quarter. However, depending on your location, you may not see the same side of the moon as someone else. Some people may see the right side, while you could see the left.

Waxing Gibbous:

This phase occurs between the First Quarter phase and the upcoming Full Moon phase. During this phase, the Moon begins to grow larger in a convex shape, with only a sliver of it not being seen. Once the moon becomes fully illuminated, the next phase in the cycle will begin.

Full Moon:

This arguably the most popular phase of the moon to most people is the Full Moon. As you may have guessed it, a full moon occurs when the Moon is completely visible and illuminated by the sun due to being on opposite sides of the Earth.

A supermoon is when the Moon is at its closet point to the Earth.

A micro-moon is when the Moon is at its furthest point from the Earth.

The Moon will also turn eerily red when it passes through the Earth’s shadow. This is called a lunar eclipse.

Waning Gibbous Moon:

In this phase, the Moon’s shape is decreasing in the opposite manner of the Waxing Gibbous phase. Basically, waxing means increasing and waning means decreasing.

Third Quarter Moon:

This is the exact opposite of the First Quarter phase with the other half side of the Moon being illuminated. Also, means that the lunar cycle is 3/4th of the way through.

Waning Crescent Moon:

The last phase of the lunar cycle, this phase begins when the sun illuminates less than half of the moon. We can also see the Earthshine effect in this phase as well.

Moon Phase Complication

The earliest example of a mechanical moon phase complication was found in the Antikythera. This was an Ancient Greek mechanism that helped people predict astronomical events such as the different moon phases and eclipses.

During the Renaissance, the moon phase complication began to be integrated into astronomical clocks built into the churches and cathedrals of Europe. The clocks were based on the belief that the Earth was the center of the universe while the rest of the solar system orbited around it. However, the clocks dwindled in numbers once scientist disproved this theory.

By the 20th century, the moon phase complication began to be incorporated into wristwatches. While it was no longer a needed means to keep track of time, it was still sought after due to the allure of the cosmos and the artistic nature of the complication.

Throughout the history of the moon phase complication, the moon has been depicted in several ways. Ranging from that of a cherub during the 16th and 17th centuries, to a more modern-day design that depicts the moon in a more realistic nature. Some designs even feature its craters.

The moon phase complication shows the current phase of the Moon as you would see it in the sky. As we see the Moon orbit around the Earth, you can also look down at your watch and see that the Moon is moving there throughout the month as well. The watch’s “Moon” is typically displayed in an aperture on the dial.

On the typical moon phase watch is a disc that has two identical moons on it. The disc will rotate one complete cycle every 29 ½ days. The waxing and the waning phase of the moon is accounted for by the curved edges of the aperture.

A true lunar cycle, however, is actually 29.53 days. The extra .03 days per month would cause the moon phase watch cycle to be off by a full day every thirty-one and a half months. Fortunately, watchmakers have made improvements on the complication to allow it be accurate for much longer, some even boasting over 1,000 years of accuracy.


Although we no longer need to keep track of the Moon’s rotation and cycles to tell the time or month, the moon phase is still one the most charming and sought out complications. The charm of a moon phase will always be timeless and the design and artistry of the complication will always catch the eye of those who appreciate the beauty of timepieces.

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Ivan Brozincevic · June 14, 2019 at 4:59 PM

In my culture, we use the word moon instead of a month. I never thought of the meaning of the word until now. Thanks for sharing this article. It was indeed a quite confusing ending, yet it’s cool to understand how we used to keep time using the magic of our moon.

    Jerry Strickland · June 17, 2019 at 11:18 PM

    Thanks for reading Ivan! Glad you learned something about this particular complication and a little bit about the moon.

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