Model History
Presented at Watches & Wonders 2021, the Luna Magna puts Arnold & Son's cherished "astronomy" pillar at the center of the dial with an unusual technical solution: instead of the customary painted disc that slides behind an aperture to simulate the moon phases, the model uses an actual three-dimensional sphere, made half of marble (the illuminated side) and half of aventurine (the shadowed side), which physically rotates on its own axis following the Moon's synodic cycle.
The sphere, just 12 mm in diameter, occupies an unusually large portion of the blue aventurine dial with its starry-sky effect, making the moon phase the undisputed protagonist of the dial's reading rather than a small secondary detail. A complementary moon-age indicator, placed on the case back, allows the exact day of the current lunar cycle to be read precisely.
The hand-wound A&S1021 calibre drives this mechanism with high astronomical precision: a one-day discrepancy takes an average of 122 years to accumulate, a figure that places the Luna Magna among the most accurate moon-phase complications the brand has produced. The 44 mm case in 18-carat rose gold and the limited production of 28 pieces underscore the model's collector's-piece nature.
Technical Specifications
Main Executions
Representing the Moon with an actual sphere rather than a flat disc might seem an obvious idea, but it's mechanically far more complex: the sphere must rotate on its own axis while advancing through the phase cycle, within a space of just a few millimeters beneath the crystal — one of the reasons this solution remains rare in watchmaking, despite its clear visual effectiveness.