Launched in 2002, the ‘Celestial’ is one of the most important horological complications ever developed. This astronomical wristwatch borrows the principle of the celestial canopy from the most complicated wristwatch ever produced by Patek Philippe - reference 5002, the Sky Moon Tourbillon. The nocturnal sky of the northern hemisphere rotates to show the apparent angular motion of the stars and moon as well as the progression of the phases of the moon. Hours and minutes are displayed by two pierced white hands. A delicate elliptical contour on the inside of the glass frames the portion of the sky visible from all cities sharing the latitude of Geneva. To determine the highest possible accurateness for the astronomical displays, the engineers of Patek Philippe researched 25 trillion (25,000,000,000,000) ratio combinations, showing the enormous horological challenge the model represents.