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Cartier Ronde Jour et Nuit New White gold 42mm Manual winding United States of America, Florida, Plantation
TOP
Cartier Ronde Jour et Nuit
$18,995
Professional dealer
60
US
Audemars Piguet Royal Oak Perpetual Calendar 26574OR.OO.1220OR.01 Unworn Rose gold 41mm Automatic United States of America, New York, NEW YORK
TOP
Audemars Piguet Royal Oak Perpetual Calendar 41mm Rose Gold...
$172,750
Free shipping
Professional dealer
485
US
Eterna Tangaroa 2949.41.16.0277 New Steel 42mm Automatic
TOP
Eterna Moonphase Chronograph 42mm Triple Calendar
$2,899
Professional dealer
22
HK
Girard Perregaux Vintage 1945 90275-52-111-BA6A Unworn Rose gold 36mm Automatic
TOP
Girard Perregaux Vintage 1945 XXL Perpetual Calendar Equation...
$27,558
Professional dealer
23
CH
Patek Philippe Perpetual Calendar Chronograph 3970 J Unworn Yellow gold 36mm Manual winding United States of America, New York, Westchester
Patek Philippe Perpetual Calendar Chronograph
$105,000
Professional dealer
6
US
Audemars Piguet Royal Oak Perpetual Calendar 26574ST.OO.1220ST.02 Very good Steel 41mm Automatic United States of America, Florida, Miami
Audemars Piguet Royal Oak Perpetual Calendar
$114,995
Professional dealer
 
US
A. Lange & Söhne 1815 421.025 New Platinum 42mm Manual winding United States of America, Arizona, Scottsdale
A. Lange & Söhne 1815 Rattrapante Perpetual Calendar
$236,900
Professional dealer
5
US
Jaeger-LeCoultre Master Calendar Q151242A Very good Rose gold 40mm Automatic United States of America, Pennsylvania, Bala Cynwyd
TOP
Jaeger-LeCoultre Master Q151242A
$14,950
Free shipping
Professional dealer
1451
US
IWC Portuguese Grande Complication IW377402 Very good Rose gold 45mm Automatic United States of America, California, Los Angeles
IWC Portuguese Grande Complication IW377402 Minute Repeater RG
$108,700
Professional dealer
80
US
A. Lange & Söhne Datograph 740.036 Very good Platinum 42mm Manual winding United States of America, Illinois, BUFFALO GROVE
A. Lange & Söhne Datograph Perpetual Tourbillon Platinum 42mm...
$328,750
Free shipping
Professional dealer
259
US
Jaeger-LeCoultre Master Eight Days Perpetual Q1612420 New Rose gold 40mm Manual winding United States of America, Illinois, Chicago
Jaeger-LeCoultre Master Eight Days Perpetual
$23,310
Professional dealer
19
US
Breguet Classique 3130BB/11/986 Very good White gold 39mm Manual winding United States of America, Massachusetts, Boston
Breguet Classique Power Reserve Moonphase
$12,500
Professional dealer
156
US
Patek Philippe Perpetual Calendar Chronograph 3970E Good Yellow gold 36mm Manual winding United States of America, California, Beverly Hills
Patek Philippe Perpetual Calendar Chronograph
$89,500
Professional dealer
141
US
Patek Philippe Perpetual Calendar Chronograph 5270R-001 New Rose gold 41mm Manual winding United States of America, New York, NY
Patek Philippe 5270R-001 Perpetual Calendar Chronograph
$145,950
Professional dealer
18
US
Patek Philippe Nautilus 5726/1A-010 Unworn Steel 40.5mm Automatic United States of America, Florida, Miami
Patek Philippe Nautilus Tiffany & CO. RARE SET
$239,885
Professional dealer
 
US
Harry Winston Midnight MIDQMP39WW001 Very good White gold 39mm Quartz United States of America, Florida, Coral Gables
Harry Winston Midnight Moon Phase MIDQMP39WW001
$13,999
Professional dealer
94
US
Longines Master Collection L27734920 New Steel 42mm Automatic United States of America, California, San Mateo
TOP
Longines The Longines Master Collection Complications Automati...
$2,829
Free shipping
Professional dealer
4098
US
Martin Braun MBA88 Very good Rose gold 44mm Automatic United States of America, California, Los Angeles
Martin Braun SELENE FC-B MOON PHASE MBA88 METEORITE 18K ROSE GOLD
$16,700
Professional dealer
80
US
Jaeger-LeCoultre Master Ultra Thin Moon Q1368420 Very good Steel 39mm Automatic United States of America, Illinois, BUFFALO GROVE
Jaeger-LeCoultre Master Ultra Thin Moon Stainless Silver 39mm...
$7,750
Free shipping
Professional dealer
259
US
Vacheron Constantin Historiques 37150 Very good Yellow gold 36mm Manual winding United States of America, New York, New York
TOP
Vacheron Constantin Historiques Triple Date Calendar 18K...
$15,800
Professional dealer
14
US
Glashütte Original Senator Panorama Date Moon Phase 100-04-32-12-04 Very good Steel 40mm Automatic United States of America, Massachusetts, Boston
Glashütte Original Senator Panorama Date Moon Phase
$5,999
Professional dealer
156
US
Jaeger-LeCoultre Grande Reverso Calendar Q3758420 Very good Steel 41.6mm Manual winding United States of America, South Carolina, Brooklyn
TOP
Jaeger-LeCoultre Grande Reverso Calendar
$7,550
Private Seller
 
US
Patek Philippe Annual Calendar 5146J-010 Very good Yellow gold 39mm Automatic United States of America, California, Beverly Hills
Patek Philippe Yellow Gold Annual Calendar Watch Ref. 5146
$29,500
Professional dealer
86
US
Audemars Piguet Royal Oak 26603OR.OO.D092CR.01 Unworn Rose gold Automatic United States of America, Florida, Miami
Audemars Piguet Royal Oak Equation Of Time
$115,995
Professional dealer
 
US
Jaquet-Droz Astrale J012630270 New Steel 43mm Automatic United States of America, Illinois, Chicago
Jaquet-Droz Astrale
$10,740
Professional dealer
19
US
Longines Master Collection L27384713 New Steel 41mm Automatic United States of America, California, San Mateo
TOP
Longines Master Collection Moonphase Automatic White Dial...
$3,199
Free shipping
Professional dealer
4098
US
Ulysse Nardin Moonstruck 1062-113 Very good Rose gold 46mm Automatic United States of America, California, Los Angeles
Ulysse Nardin Moonstruck 1062-113 18k Rose Gold Blue MOP LTD
$48,700
Professional dealer
80
US
IWC Portuguese Perpetual Calendar IW502306 Very good Rose gold 44mm Automatic United States of America, Illinois, BUFFALO GROVE
IWC Portugieser Perpetual Calendar Rose Gold 44mm IW502306
$23,250
Free shipping
Professional dealer
259
US
Patek Philippe Perpetual Calendar 5059R-001 Unworn Rose gold 36mm United States of America, California, Beverly Hills
Patek Philippe Perpetual Calendar Retrograde
$44,500
Professional dealer
141
US
IWC Portofino Hand-Wound IW544801 Very good Steel 46mm Manual winding United States of America, Massachusetts, Boston
IWC Portofino
$6,250
Professional dealer
156
US
Patek Philippe Perpetual Calendar Chronograph 5270P-001 New Platinum 41mm Manual winding United States of America, New York, NY
Patek Philippe 5270P-001 Perpetual Calendar Chronograph
$179,500
Professional dealer
18
US
Blancpain Le Brassus 4276-3642A-55B Very good Rose gold 42mm Automatic United States of America, Georgia, Atlanta
TOP
Blancpain Le Brassus Moonphase 4276-3642A-55B Watch with...
$17,500
Free shipping
Professional dealer
963
US
Patek Philippe Nautilus 5712G-001 Tiffany & Co. Unworn White gold 40mm Automatic United States of America, Florida, Miami
Patek Philippe Nautilus Tiffany & Co. RARE SET
$175,985
Professional dealer
 
US
Breguet Classique 3330BA/1E/986 New Yellow gold Automatic United States of America, Illinois, Chicago
Breguet Classique
$20,280
Professional dealer
19
US
Jaquet-Droz Grande Seconde J007530240 New Steel 43mm Automatic United States of America, California, Burlingame
TOP
Jaquet-Droz Grande Seconde Moon Silver 43mm Automatic Silver...
$11,329
Free shipping
Professional dealer
4098
US
Blancpain Le Brassus 4286P 3442A -55B Very good Automatic United States of America, California, Los Angeles
Blancpain LE BRASSUS PERPETUAL CALENDAR SPLIT SECOND CHRONOGRA...
$42,700
Professional dealer
80
US
Patek Philippe Annual Calendar 5036/1G Good White gold 37mm Automatic United States of America, Illinois, BUFFALO GROVE
Patek Philippe 5036/1G White Gold 37mm box and archive papers
$36,750
Free shipping
Professional dealer
259
US
Patek Philippe Perpetual Calendar Chronograph 5204/1R-001 New Rose gold 40mm Manual winding United States of America, California, Beverly Hills
Patek Philippe Perpetual Calendar Split Chronograph
$259,500
Professional dealer
141
US
Parmigiani Fleurier Tonda PFC272-1200200-HA1441 New White gold 40mm Automatic United States of America, Florida, Sarasota
TOP
Parmigiani Fleurier Tonda Quator 18k White Gold Annual...
$14,499
Free shipping
Professional dealer
925
US
Blancpain Léman Fly-Back 2585F-1130-71 Very good Steel United States of America, Massachusetts, Boston
Blancpain Leman Perpetual Calendar Flyback
$13,500
Professional dealer
156
US
Patek Philippe Annual Calendar 4936G Very good White gold 37mm Automatic United States of America, New York, NY
Patek Philippe ANNUAL CALENDAR 37MM 4936G 18K WHITE GOLD MEN'S...
$31,500
Professional dealer
119
US
Patek Philippe Nautilus 3712/1A New Steel 42mm Automatic United States of America, Florida, Miami
Patek Philippe Nautilus SEALED
$185,925
Professional dealer
 
US
Breguet Classique 9088BR52964DD0D New Rose gold 30mm Automatic United States of America, Illinois, Chicago
Breguet classique
$18,655
Professional dealer
19
US
Zenith 18.2320.692/80.C713 New Rose gold 36mm Automatic United States of America, California, San Mateo
TOP
Zenith ELITE LADY MOOPHASE 18 KT GULD 18.2320.692/80.C713 -...
$8,199
Free shipping
Professional dealer
4098
US
Arnold & Son True Moon 1TMAS.S03A.C79B New Steel 46mm Automatic United States of America, California, Los Angeles
Arnold & Son True Moon 1TMAS.S03A.C79B Meteorite Stone Retail...
$13,700
Professional dealer
80
US
Patek Philippe Annual Calendar 5396G Good White gold 39mm Automatic United States of America, Illinois, BUFFALO GROVE
Patek Philippe Annual Calendar White Gold 39mm 5396G Full Set...
$39,250
Free shipping
Professional dealer
259
US
Patek Philippe Perpetual Calendar 5327R-001 New Rose gold 39mm Automatic United States of America, New York, NY
Patek Philippe 5327R-001 Perpetual Calendar
$75,495
Professional dealer
18
US
Blancpain Villeret 6659-3631-55B Unworn Rose gold 42mm Automatic United States of America, Florida, Sarasota
TOP
Blancpain Villeret Quantieme Perpetual 8 Days 18k Gold...
$37,999
Free shipping
Professional dealer
925
US
Audemars Piguet Royal Oak Day-Date 25594SA Very good Yellow gold 36mm Automatic United States of America, California, Beverly Hills
Audemars Piguet Yellow Gold, Day-Date, Moonphase Royal Oak...
$33,000
Professional dealer
86
US
Jaeger-LeCoultre Master Hometime Q1718420 Very good Steel 39mm Automatic United States of America, Massachusetts, Boston
Jaeger-LeCoultre Master Hometime Limited Edition of 120 Pcs
$6,750
Professional dealer
156
US
Patek Philippe Nautilus 5712/1A-001 Very good Steel 40mm Automatic United States of America, Florida, Miami
Patek Philippe Nautilus
$117,984
Professional dealer
 
US
Parmigiani Fleurier Tonda PFC272-1002400-ha1241 New Rose gold 42mm Automatic United States of America, Illinois, Chicago
Parmigiani Fleurier Tonda
$19,250
Professional dealer
19
US
Longines Heritage L48264922 New Steel 40mm Automatic United States of America, California, San Mateo
TOP
Longines Heritage Classic Automatic Beige Dial Mens Watch -...
$1,859
Free shipping
Professional dealer
4098
US
Audemars Piguet Jules Audemars 26391OR.OO.D088CR.01 Unworn Rose gold 41.3mm Automatic United States of America, California, Los Angeles
Audemars Piguet Jules Audemars Dragon 26391oR.00do88cr.01 18k...
$48,700
Professional dealer
80
US
Jaeger-LeCoultre Duomètre 6042521 Very good Rose gold 39mm Manual winding United States of America, Illinois, BUFFALO GROVE
Jaeger-LeCoultre Duometre Lunaire 39MM 18k rose Gold Complete...
$28,250
Free shipping
Professional dealer
259
US
Patek Philippe Annual Calendar 5396G-011 New White gold Automatic United States of America, New York, NY
Patek Philippe 5396G-011 Annual Calendar
$43,750
Professional dealer
18
US
Patek Philippe Gondolo 5135G-010 New White gold 51mm Automatic United States of America, California, Beverly Hills
Patek Philippe Gondolo Annual Calendar Slate Dial
$31,950
Professional dealer
141
US
Patek Philippe Perpetual Calendar 5320G-001 New White gold 40mm Automatic United States of America, New York, Brooklyn
Patek Philippe Perpetual Calendar 5320G Fully Sealed November...
$77,691
Professional dealer
33
US
Patek Philippe Nautilus 5712R-001 Very good Rose gold 40mm Automatic United States of America, Texas, Houston
TOP
Patek Philippe Nautilus
$78,500
Private Seller
 
US
Patek Philippe Nautilus 5724R-001 Unworn Rose gold 40mm Automatic United States of America, Florida, Miami
Patek Philippe Nautilus
$254,985
Professional dealer
 
US
Audemars Piguet Royal Oak Perpetual Calendar 26585CE.OO.1225CE.01 Unworn Ceramic United States of America, New York, New York
Audemars Piguet Royal Oak Perpetual Calendar 26585CE Unworn
$399,995
Free shipping
Professional dealer
561
US
Audemars Piguet Royal Oak Perpetual Calendar 26579CE.OO.1225CE.01 New Ceramic 41mm Automatic United States of America, New York, New York
Audemars Piguet Royal Oak Perpetual Calendar 41mm Titanium...
$190,000
Free shipping
Professional dealer
85
US
Franck Muller Long Island 1200 QP Very good White gold 55mm Automatic United States of America, California, Los Angeles
Franck Muller Long Island Perpetual 1200QP WGBL 18k White Gold
$21,700
Professional dealer
80
US
F.P.Journe Very good Platinum 40mm Automatic United States of America, Illinois, BUFFALO GROVE
F.P.Journe CLASSIQUE DIVINE PLATINUM MOONPHASE 40MM FULL SET
$67,250
Free shipping
Professional dealer
259
US

Moon Phase Watches: Under the Lunar Spell

Humans have always had a fascination with the Moon. The first moon phase watches appeared back in the 1500s. A few modern pieces will accurately display the Moon's phase for over 2 million years and mark the pinnacle of haute horlogerie.


5 Reasons to Buy a Moon Phase Watch

  • One of the most popular complications
  • Prices beginning under 1,100 USD
  • Top models often feature a perpetual calendar
  • Andreas Strehler: A record-breaking moon phase, accurate for 2 million years
  • Luxury timepieces from A. Lange & Söhne and Patek Philippe

A Moon Phase for Every Budget

It takes the Moon 29 days, 12 hours, 44 minutes, and 3 seconds to complete one full cycle. During that time, it goes through four major phases: New Moon, Waxing Moon, Full Moon, and Waning Moon. A moon phase display makes it easy to keep track of the Moon's current stage in the cycle and is one of the most popular complications. However, it's actually not as complex as it might sound.

Numerous manufacturers produce moon phase watches, covering a wide price range. The most affordable models start at less than 1,100 USD, while more exclusive timepieces can cost upwards of 110,000 USD. Watches on the upper end of the price range often feature a unique moon phase mechanism and perpetual calendar. One prominent example is the Richard Lange Perpetual Calendar Terraluna from A. Lange & Söhne. This model has an orbital moon phase display on the reverse side of its case. Thanks to its intricate mechanics, this display only requires manual correction every 1,058 years. More conventional moon phase displays tend to deviate by about eight hours per year, meaning they will be off by one full day after three years. Of course, all this technical mastery has its price: the Richard Lange Perpetual Calendar Terraluna costs around 178,000 USD in red or white gold.

The record for the world's most precise moon phase watch belongs to Andreas Strehler and his Sauterelle à lune perpétuelle. This timepiece's astounding moon phase display only deviates by one day every 2.06 million years. Strehler's Sauterelle à heure mondiale takes his extraordinary moon phase mechanism and adds a world time function that sits on the case back and displays the time in 24 time zones simultaneously. You can call the Sauterelle à heure mondiale your own for around 125,000 USD (excluding VAT). The Sauterelle à lune perpétuelle costs about 98,000 USD in red gold and 113,000 USD in platinum, also excluding VAT.


How much do moon phase watches cost?

Model Price (approx.) Other functions
Glycine Combat Classic Moonphase 1,100 USD Date
Oris Artelier Complication 1,600 USD Date, day, second time zone
Mido Baroncelli Moon Phase 1,800 USD Chronograph, calendar
Maurice Lacroix Les Classiques Moonphase 2,200 USD Pointer date
Frederique Constant Slimline Moonphase Manufacture 2,800 USD Pointer date
Longines Master Collection 3,000 USD 24-hour display and retrograde small seconds, date, and day displays
Patek Philippe ref. 5205 42,500 USD Annual calendar, 24-hour display
A. Lange & Söhne Grand Lange 1 Moonphase "Lumen" 78,000 USD Oversize date, luminous displays

Prices for Affordable Models

Moon phase watches don't have to cost an arm and a leg, as demonstrated by Swiss manufacturers like Glycine, Maurice Lacroix, and Mido. Glycine's Combat Classic Moonphase is among the most affordable models and costs under 1,100 USD, even with gold plating. The automatic caliber GL280 powers this timepiece and provides it with its date display.

You can save even more by purchasing a moon phase watch with a quartz caliber. For example, the 41-mm Certina DS-8 Moon Phase goes for under 560 USD in mint condition. The version with a chronograph function for measuring periods of time sells for about 670 USD. At the very bottom of the price range, you'll find quartz watches from Casio, Jacques Lemans, or Henry that only cost around 170 USD.

Overview: Affordable Moon Phase Watches

  • Under 1,100 USD: Glycine Combat Classic Moonphase with an automatic caliber
  • Under 560 USD: Certina DS-8 Moon Phase with a quartz movement
  • Around 170 USD: Quartz watches from Casio or Jacques Lemans

Mid-Range Moon Phase Watches

Maurice Lacroix, Mido, Frederique Constant, and Longines all produce relatively inexpensive moon phase watches. Each of these brands is famous for crafting high-quality mechanical timepieces that offer fantastic value for money.

The Genevan brand Frederique Constant is synonymous with affordable luxury and classically elegant designs. Their Slimline Moonphase Manufacture model with a pointer date has a 42-mm stainless steel case and costs as little as 2,800 USD. At only 2,200 USD, pre-owned pieces are even more budget-friendly. The rose gold edition falls in a similar price range. Frederique Constant also produces the Slimline Perpetual Calendar Manufacture, one of the most affordable perpetual calendars in the industry. The gold-plated version changes hands for roughly 7,800 USD.

Swiss manufacturer Maurice Lacroix also produces economical moon phase watches. One example is the 40-mm Les Classiques Moonphase with a pointer date. This stainless steel timepiece comes on a leather strap or stainless steel bracelet. With a price tag of about 2,200 USD, new pieces are remarkably affordable.

A never-worn Oris Artelier Complication requires an investment of around 1,600 USD. If you're lucky, you might even find a pre-owned piece selling for less than 1,100 USD. This dress watch features a day-date display and a second time zone in addition to a moon phase display. Oris outfits this timepiece with the caliber 781, which is based on the Sellita SW 200-1.

An Overview of Mid-Range Moon Phase Watches

  • Under 1,700 USD: Oris Artelier Complication
  • Around 2,200 USD: Maurice Lacroix Les Classiques Moonphase
  • Around 2,800 USD: Frederique Constant Slimline Moonphase Manufacture

Mido and Longines Models with a Chronograph and Calendar

Both Longines and Mido belong to the Swatch Group and combine moon phase displays with chronographs and calendars. The Valjoux 7751 ticks away inside these timepieces. It has a dual 12-hour counter and moon phase display at 6 o'clock and a combined 24-hour display and small seconds at 9. The day and month displays are integrated into the 30-minute counter at 12. There's also an additional central hand that points to the date around the dial's edge.

The Mido Baroncelli Moon Phase comes in stainless steel or with a rose gold PVD coating. You also can choose between a leather strap or stainless steel bracelet. Plan to spend around 1,800 USD on this Mido moon phase watch in mint condition. The model with a PVD coating demands some 2,100 USD new.

Longines offers a comparable chronograph in their Master Collection. This classic watch boasts a moon phase display, calendar, and stopwatch function. At about 2,700 USD, a never-worn Longines model is a bit more expensive than its Mido counterpart. However, pre-owned pieces sell for only 1,900 USD.

Longines' catalog also contains a moon phase watch with four retrograde displays: a small seconds, a pointer date, a second time zone, and a day display. Each display has a pointer that returns to its starting position once it reaches the end of the scale. Longines equips this timepiece with the caliber L707, based on the ETA A07.L31. This movement has a 48-hour power reserve and ticks at 28,800 alternations per hour. You can call this watch your own for under 2,200 USD pre-owned and approximately 3,000 USD new.


High-End Moon Phase Watches

Timepieces from Patek Philippe and A. Lange & Söhne represent the crème de la crème of watchmaking. Patek Philippe has had a reputation for crafting exquisite timepieces for over 180 years. The company is more than familiar with the moon phase function and often combines it with an annual calendar in the watches of their Complications collection. Annual calendars only require manual correction once a year.

The Patek ref. 5205 also features a 24-hour display. This luxury watch's calendar function occupies three windows: There's the day at 10, date at 12, and month at 2 o'clock. Rose gold editions tend to cost around 42,500 USD, regardless of condition. The ref. 5396 also boasts an annual calendar and 24-hour display. Its date display sits at 6 o'clock, while the day and month are located on the dial's upper half. This timepiece requires an investment of about 41,000 USD new and 35,000 USD pre-owned. Finally, the ref. 5146 comes with an annual calendar but lacks a 24-hour display. It uses subdials for the month and day displays. The yellow gold version sells for between 25,000 and 34,000 USD.

The Lange 1 was A. Lange & Söhne's first wristwatch and has since come to define this German luxury watch manufacturer. Off-center displays and an outsize date characterize this timepiece. Over time, the Lange 1 has developed into a comprehensive collection of watches. Highlights include timepieces with a perpetual calendar, tourbillon, and/or moon phase. Of the moon phase watches, the Grand Lange 1 Moon Phase "Lumen" sets itself apart with its translucent dial. It allows through just enough light to energize the watch's luminous elements, such as its outsize date and moon phase display. What's more, this particular Lange 1 was A. Lange & Söhne's first wristwatch to feature glow-in-the-dark components. Be sure to have around 78,000 USD on hand for a mint-condition model.

The Grand Lange 1 Moon Phase and Lange 1 Moon Phase both have more classic designs than the "Lumen." Furthermore, the 38.5 and 41-mm editions are much more affordable than their luminescent counterpart. All three of these moon phase watches share the same manual in-house caliber with a 72-hour power reserve. This movement's moon phase display has to be corrected by hand every 122.6 years . You can purchase a never-worn Lange 1 Moon Phase in white gold for roughly 35,000 USD. Pre-owned pieces change hands for some 31,000 USD. Prices for the rose gold edition range from 20,500 to 33,500 USD, depending on its condition. If you prefer platinum watches, take a look at the Grand Lange 1 Moon Phase. This model costs about 46,000 USD new and 43,000 USD pre-owned.

Moon Phase Watches from A. Lange & Söhne and Patek Philippe

  • Around 33,000 USD: A. Lange & Söhne Lange 1 Moon Phase
  • Around 42,000 USD: Patek Philippe ref. 5205
  • Around 78,000 USD: A. Lange & Söhne Grand Lange 1 Moon Phase "Lumen"

How do moon phase watches work?

Moon phase watches essentially function like any other mechanical watch. However, unlike conventional three-hand models, these timepieces feature a moon phase display, often in the form of a disc. The disc sits below a semicircular opening and has two moons, only one of which is visible at any given time. Watch manufacturers use two moons instead of one because a complete lunar cycle lasts 29.5 days. Since there is no gear with 29.5 teeth, they use a gear with 59 teeth . Each day, the watch movement moves this gear forward by one tooth, thus completing two whole cycles per full rotation. This process usually takes place around midnight and is often linked to the date display.

This is the simplest of all moon phase displays, and it has an annual deviation of eight hours. This means it will be a full day off after three years. This is a result of the fact that an actual lunar cycle is 44 minutes and 3 seconds longer than the 29.5-day system employed by these mechanisms.

The Moon's individual phases are determined by its orbit around the Earth and its position relative to our planet and the Sun. If the Sun is shining on the Earth-facing side, we see a Full Moon. If it's shining on the opposite side, the Moon seems to disappear. This is known as a New Moon. The Moon and Earth rotate at the same rate, which is why we only ever see one side of the Moon from Earth.