Know Your Watches: What Is A Moonphase Watch?

History stands as witness that watchmakers have drawn inspiration from this celestial body giving birth to moon phase watches. By just a glance at your wrist, you can ascertain which phase the moon is currently in and revel in the beauty of the glistening Luna. This type of watch is perhaps the most poetic in its graphical representation of the passage of time, as opposed to the more precise and sterile hands and numbers that other complications use. It is a more whimsical and artistic complication, one that is fun to own, linking us with our sky-watching ancestors and a lineage of watchmakers and artisans all at once.

In this article we give our luminous nighttime friend the attention it deserves by decoding what is a moon phase watch and some prime examples of this sophisticated engineering and eye catching designs by watchmaking maisons. 

What is a Moon phase?

By definition, a moon phase watch is one that relays the 29.5-day lunar cycle by exhibiting the current moon phase in an aperture on the dial which is also known as a moon phase complication. A moon phase, is mankind’s practical way of describing the luminous (or visible) portion of the moon as it orbits the planet. There are two basic types of watches with moon phase complications. The most common is known as a “bosom” moon phase watch, which takes a graphical approach by physically showing the moon in its various phases inside a crescent-shaped aperture. The other type is known as a “radial” moon phase watch, and it uses an indicator hand to track the lunar cycle. 

How It Works

One of the earliest watch mechanisms ever developed, moon phase complications typically involve placing two identical moons on a disc under the dial. Controlling the movement of the disc is a 59-tooth driving wheel, which uses a mechanical finger to advance the disc once per day. After a single 29.5 day lunar cycle is completed, the second moon appears in the aperture, hence the total of 59 teeth (29.5 x 2). Naturally, the details of the underlying moon disc will vary based on the design of the dial and aperture, while the driving wheel remains a constant. While several watchmaking brands offer moon phase timepieces, we bring to you 3 pieces that truly embody the essence of the moon phase. 

De Bethune

DB25 Moon Phase Reference: DB25LRS1V1

Encapsulated in precious materials, an incomparable understanding of the past and present of watchmaking inhabits this radiant piece. A white gold case measuring 44 mm contains a silver toned, hand-guilloche dial with 12 radiating sectors. The De Bethune signature star studded sky in mirror polished flame blued steel set with yellow gold stars along with spherical moon phase indicator in palladium and flamed blued steel at 12 o’clock. The open back case is forged in solid white gold and reveals the heart of the watch. Powered by the DB2109V4 calibre the mechanical hand wound movement features 43 jewels. The DB25 Moon phase effortlessly combines roundness, depth and textures to set the scene of time with an absolute clarity.

Sarpaneva

Lunations

If there is one brand that is considered a master of moon phase, it is Sarpaneva. It distils all 30 years of Stepan Sarpaneva’s professional watchmaking expertise into every timepiece making it a true icon of horology. Sarpaneva Lunations is the very first Sarpaneva ultra-precise in house calibre which lasts 29 days, 12 hours, 44 minutes and 2.3 seconds, which means it needs to be adjusted for a single day of error only once every 14,000 years. 

Pulling the crown at 4 o’clock out to the first position allows the wearer to set the phases of the moon display. An integrated phases of the moon scale, engraved on the back of the watch provides additional guidance on getting the display as close to the actual lunar cycle as possible. Sarpaneva Lunations can also be easily customised to reflect the lunar cycle in both northern and southern hemispheres. 

Arnold & Son

Perpetual Moon 38 Mintnight

A poetic ode to the mysterious serenity of midnight, this new women’s complication timepiece from Arnold & Son uses diamonds, mother-of-pearl and ruthenium crystals to illustrate its beauty. Measuring 38 mm in diameter and 10.44 mm thick, the case of the Perpetual Moon 38 Mintnight is fashioned from a block of white gold. Its bezel, four horns and crown host a total of 80 brilliant-cut diamonds. When added to the 22 diamonds adorning its buckle, they amount to a total weight of 2.57 carats. These gemstones pave the way for the ornamental riches that have been lavished on this delicate complication. 

The Swiss manufacture created a specific calibre, the smallest in its collection, especially for the Perpetual Moon 38. The proportions of the A&S1612 calibre, which measures 29.4 mm, were designed with the case in mind. This manually wound movement with an autonomy of 90 hours perpetuates the range of Arnold & Son calibres with impressive power reserves.