Timekeeping was born out of desire to make sense of the movement of the sun, the moon and the constellations. When the early horologists graduated from the sundial to gears and hands, one of the important events they tracked was the lunar cycle. This is because although the sun’s arc dictates days and seasons, the moon was the first method of telling the passing of months. The moon has always played a major role in man’s movements and daily existence, from the ebb and flow of tides to religious ceremonies, crop harvests and maritime navigation.
A moon phase watch shows the moon’s cycle as you see it in the sky, displayed in an aperture on the dial. This type of watch is representation of the passage of time and the most graphical as opposed to the more precise hands and numbers that other time pieces use. It is a whimsical and artistic complication, one that is fun to own, linking us with our sky watching ancestors.
The Moon has phases because it orbits Earth, which causes the portion we see illuminated to change. The Moon takes 27.3 days to orbit Earth, but the lunar phase cycle, from new Moon to new Moon, is 29.5 days. The Moon spends the extra 2.2 days “catching up” because Earth travels about 45 million miles around the Sun during the time the Moon completes one orbit around Earth. A “moon phase” is the lighted area of the moon that is visible as it travels around the earth. Astronomers have several names for the appearance of the moon throughout its cycle, from waxing gibbous to waning crescent, there are really only four phases you really need to know.
At the new Moon phase, the Moon is so close to the Sun in the sky that none of the side facing Earth is illuminated. In other words, the Moon is between Earth and Sun. As the moon travels through its monthly orbit, more of its surface becomes illuminated by the sunknown as “waxing”. At first quarter, the half-lit Moon is highest in the sky at sunset, then sets about six hours later. At full Moon, the Moon is behind Earth in space with respect to the Sun. As the Sun sets, the Moon rises with the side that faces Earth fully exposed to sunlight. Last quarter is when the left-hand side is visible, waning, until it finally goes back to a new moon again.
The moonphase was commonly found in the more complicated pocket watches in the late 19th and early 20th centuries before it changed to the wristwatch.
Behind the dial of a typical moonphase watch is a disc with two identical moons on it. This disc rotates one complete cycle every twenty-nine and a half days, with the waxing and waning face of the moon accounted for by the curved edges of the dial aperture. The true lunar cycle lasts 29 days, 12 hours and 44 minutes, so 29.53 day. In reality, the watch isn’t this cooperative with the moon disc, originally driven by a 59-tooth gear that advanced one notch by a mechanical finger every 24 hours, corresponding to one full rotation for the entire lunar cycle. This was proving to be off by .03 days per month means that the entire moon phase cycle will be off by one full day every two years, seven and a half months, requiring a manual correction roughly once every two-and-a-half years. A 135-tooth gear was introduced. This improvement increased the accuracy so that the moon phase complication will only be off by a day once every 122 years.
Watch Agency’s pick of our favourite Moonphase watches.
ROLEX CELLINI MOONPHASE
The Cellini Moonphase has a white lacquer dial with a blue enamelled disc at 6 o’clock showing the full moon and the new moon, the former depicted by a meteorite applique and the latter by a silver ring. The moonphase is read via the indicator set at 12 o’clock on the subdial, as the full moon and new moon rotate through the lunar cycle. The Cellini Moonphase also displays the date around the circumference of the dial, via a centre hand with a crescent moon at its tip.
OMEGA SPEEDMASTER MOONWATCH
The Speedmaster is one of OMEGA’s most iconic timepieces, having been a part of all six lunar missions. Taking the spirit of exploration a step further, this new Moonphase features two infinitely small yet photo-realistic moons. This 44.25 mm model features a black sun-brushed dial, with rhodium-plated indexes. At 6 o’clock is the accurate Moonphase indication, which features a metallic crystal disc microstructured to obtain a high resolution image of the moon. The stainless steel case is complemented by a black ceramic bezel ring with Liquidmetal™ tachymeter scale and presented on a black leather strap with a polished-brushed foldover clasp. Powering the timepiece is the OMEGA Co-Axial Master Chronometer 9904, which has been officially certified by METAS.
BALLON BLEU DE CARTIER WATCH
Ballon Bleu de Cartier watch, 37 mm, mechanical movement with automatic winding, moon phases. Steel case. Silvered flinqué dial, Roman numerals, moon phases at 9 o’clock, blued-steel sword-shaped hands. Sapphire crystal. Steel bracelet, 180 mm wrist circumference. Case thickness: 13 mm. Water-resistant to 3 bar (~30 metres).
PATEK PHILIPPE 5159
Patek Philippe 5159 R Perpetual Calendar Retrograde, 5159R-001, 5159R001, 18k rose gold on a strap with an 18k rose gold deployment buckle, automatic movement, day, retro date, month, moonphase, leap year, centered sweep seconds hand, half hunter case, silver dial with center guilloche, sapphire crystal, water resistant to 25 meters.
JAEGER-LECOULTRE RENDEZ-VOUS MEDIUM
A shimmering presence on the dial, the moon majestically moves over the face of this stainless steel Rendez-Vous Moon Medium watch. Its diamond setting and stainless steel bracelet add a supremely feminine, jewellery-like sophistication.Stainless Steel, Water-resistance to 3 bar.