Stellar Aspirations

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Among the lesser-known facets of the famous rivalry between 1920s-era industrialists James Ward Packard and Henry Graves Jr.—two avid collectors who each ordered successively more complicated pocket watches from Patek Philippe—is that both men set their sights on a highly personal complication: They each wanted their nec plus ultra timepiece to feature celestial time with a star chart depicting the sky over their respective homes. While astronomical complications may seem arcane to some, enthusiasts recognize (as Packard and Graves once did) that they touch our primal notions of time, which is why they can still command center stage in the most complicated timepieces today.

Even before watches and clocks had minute hands, 17th-century horologists developed gearwork to display moon phases, useful in an agrarian society lacking artificial lighting, yet hardly straightforward since the moon orbits Earth every 29-and-a-half days. Or 29 days, 12 hours, 44 minutes, and 2.9 seconds to be precise—and accuracy is the common cause of astronomy and watchmaking. Horologists have approached this mechanical challenge by increasing the fineness of their gearing. On older watches, 59 teeth were cut into a wheel with two full moons—each covered in turn—an arrangement that lost a day every couple of years. By increasing the number of teeth to 135, watchmakers have improved accuracy significantly. The large classical lunar display on the Arnold & Son HM Perpetual Moon shows the monthly waxing and waning with a lag of just one day every 122 years. That performance is matched by the Chopard L.U.C Lunar Big Date, which presents the lunar cycle on a novel “orbital” display that shows the various moon phases for both the Northern and Southern Hemispheres.

But 122 years is not the mechanical limit. Ludwig Oechslin has developed an innovative new moon-phase module for the Ochs und Junior Moon Phase that deviates by just one day in 3,478.27 years. Oechslin achieves this feat by using epicyclic gearing, in which a train of gears controls the rotation of a disc inside an internally toothed hub. The epicyclic gearing and selection of gears within it allow him to impart an extremely precise ratio of rotation between the hour hand and the lunar display: The disc revolves once every 29.5306122449 days.

For Oechslin, this mathematical feat is child’s play. He may be best remembered for the trio of astronomical watches that brought Ulysse Nardin’s mechanical watchmaking back to prominence in the 1980s and ’90s. Recapitulating the early history of astronomy, the Ulysse Nardin Tellurium Johannes Kepler, for instance, shows the apparent motion of the sun, the Earth, and the moon from a terrestrial perspective. The Moonstruck watch Oechslin conceived with Ulysse Nardin a few years ago takes up where the Tellurium left off. Earth is fixed at the center of the dial, shown from above the North Pole, with disks for the sun and the moon orbiting around it. Since Oechslin’s mechanism alters the moon phase in tandem with the lunar disk’s rotation, the wearer can see how the relative position of the sun and the moon affects the moon phase. More profoundly, the watch tracks global tides, which are caused by the combined gravitational pull of the sun and the moon on the seas. Of course, the world view shown by Oechslin’s watch is make-believe, a geocentric model predating Copernicus. Yet the watch also helps to explain why that world view was so persistent, since the information on the Moonstruck dial corresponds to Earth-based observations of the sky above.

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