Patek Philippe Watches

Sky Moon by Patek Philippe 5102

The nocturnal sky of the Northern Hemisphere in a wristwatch

Patek Philippe's Ref. 5102 Sky Moon astronomical wristwatch, featuring a large-format sky chart with an integrated moon phase display, continues a proud tradition of the company's acclaimed Geneva workshops. On October 5, 2000, Patek Philippe had unveiled the Star Calibre 2000, one of the most complicated pocket watches of all time, with a fascinating suite of astronomical indications.

It was the first timepiece ever that presented the exact configuration of the nocturnal sky with the apparent movement of the stars, the position of the moon, and its progressing phases within a lunar cycle.

Six months later, the company's watchmakers introduced the "Sky Moon Tourbillon" - a wristwatch-sized grande complication for which the astronomical functions had to be further miniaturized and integrated on the reverse side of the timepiece.

Now, this heavenly canopy can be admired on the dial side of a wristwatch - the self-winding Ref. 5102.

The celestial panorama of the Ref. 5102 Sky Moon

The Patek Philippe Ref. 5102 Sky Moon embodies a function which is highly unusual for a wristwatch. The night sky of the Northern Hemisphere rotates counter clockwise on its dial, showing the angular progression of the stars relative to the meridian passage of Sirius. At the same time, the display shows the meridian passage and phases of the moon. Two hands from the centre show the hours and minutes of mean solar time on a dial with Roman numerals.
 

The complex astronomical displays rely on a system of stacked sapphire crystal discs which rotate at different speeds and create a mesmerizing impression of depth. The celestial background is a blue sapphire crystal disc in a wheel with 279 teeth. This disc reproduces the orbit of the moon. Via a planetary gear train, it also drives a subsidiary sapphire crystal disc depicting the waxing and waning of the moon in a small round aperture. Above it, in a wheel with 356 teeth, lies a transparent sapphire crystal disc which bears the sky chart on one side and an image of the Milky Way galaxy on the other. These three discs are protected by the sapphire crystal glass with an ellipse on the inside that frames the portion of the sky visible above Geneva. For this invention, Patek Philippe was awarded Swiss Patent CH 688 171 B5.

Divine precision

This innovative mechanism achieves an astonishing degree of precision in the realm of astronomical displays. A lunar day is defined as the time between two consecutive passages of the moon across a specific meridian and on average lasts 24 hours, 50 minutes, and 28.328 seconds. A lunation - the time between two consecutive full moons - averages 29 days, 12 hours, 44 minutes, and 2.82 seconds. A sidereal day is the time it takes for a fixed star (such as Sirius) to make one complete passage across a specific meridian and averages out to 23 hours, 56 minutes, and 4.09892 seconds. These deviations from mean solar time call for appropriate step-up or step-down transmission ratios in the gear trains that transfer the force from the mainspring barrel of the movement to the individual astronomical displays. So far, some of these ratios known in horology have delivered a more accurate moon phase display and a less accurate solar day, others have reproduced the solar day more accurately than the orbit of the moon. But after having calculated more than 25 trillion (25,000,000,000,000) ratio combinations, Patek Philippe discovered the one single ratio that produces the highest degree of precision in all displays. The result surpasses all expectations:

-The lunar day is accurate to 0.05 seconds per day, 18.385 seconds per year, or 30 minutes and 38.5 seconds per century.

-The sidereal day is accurate to 0.088 seconds per sidereal day, 32,139 seconds per year, or 53 minutes and 33.9 seconds per century.

-The moon phase is accurate to 6.51 seconds per lunation.

A masterpiece of perfection

The self-winding movement of the Ref. 5102 with its Sky Moon mechanism is a masterpiece of precision mechanical engineering composed of 301 individual parts that are painstakingly finished by hand. The edges of all steel components are bevelled and polished and each tooth of each and every gear wheel is manually polished with a rotating hardwood disc. This degree of perfectionism is not a means unto itself. It reduces friction at the wheel contact points and contributes significantly to the high level of precision and longevity for which Patek Philippe watches have earned a reputation. The plate is circular-grained on both sides and the bridges are decorated with Geneva striping. Because of these intricate operations and the numerous inspections required in the course of assembly, each movement takes months to complete. The result is a flawless movement which deserves to bear the Geneva seal as an official acknowledgment of compliance with the ultimate standards of quality in mechanical timepieces.  The self-winding watch draws its power from a minirotor recessed off-centre in the movement. Even slight movements of the wrist are sufficient to supply the necessary winding energy, because the rotor is crafted from heavy 22K gold. For this reason, the movement is only 6.26 millimetres high, despite its complexity. The case, too, is remarkably slim.

Amazing technology in a fascinating package

The 18K white gold case which protects the Sky Moon movement has a diameter of 43.1 millimetres and a height of 9.78 millimetres. Its case band is decorated with a Calatrava cross pattern. The crown at 2 o'clock winds the movement and adjusts the hands. A second crown at 4 o'clock corrects the sky chart in one direction and the angular position of the moon and the moon phase in the other. The sapphire crystal case back reveals the exquisite decorations and the guilloched winding rotor of the complicated movement.

The heavens can wait

The Ref. 5102 Sky Moon is an important addition to the Patek Philippe line of complicated wristwatches. Although it is not a limited edition, annual production will be restricted in view of the effort involved in crafting, assembling, and regulating this masterpiece of horology. In return for their patience, owners will be delighted to know that they possess a very rare and unique timepiece that is in a class of its own with regard to esteem and value appreciation.

Further Reading

Patek Philippe

Complicated Wrist Watches

Giorgio Gregato, Paolo De Vecchi

Full details at: Greenwich Book

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