Yema Spacegraf Flying Tourbillon: Sidereal Time

At $16,000, the Yema Spacegraf Heure Sidérale Tourbillon Volant is the French brand’s most ambitious release for its 2026 Millésime collection. Limited to 150 pieces, it pairs a flying tourbillon with a sidereal time display, all powered by a manufacture caliber. This is a watch that measures its time against the stars. Yema positions its "Millésime" watches as the peak of its production, handcrafted and limited. This Spacegraf is the flagship, built around a historical concept from the cradle of French watchmaking. It directly references the Besançon Observatory, established in 1878 so that local watchmakers could regulate their timepieces by observing the stars. The watch translates that history into two distinct mechanical features. At 12 o’clock, a celestial disc rotates to the rhythm of the actual sky. At 6 o’clock, the dial opens to expose the beating heart of its French-made movement: a flying tourbillon.

The Heart of Yema: Calibre Manufacture Morteau CMM.32

The engine driving the Spacegraf is the Calibre Manufacture Morteau CMM.32, a movement developed with watchmaker Olivier Mory. Yema states that key components like bridges and mainplates are manufactured in its own workshops in Morteau, France. This movement is where the watch makes its technical statement. It delivers a substantial 105-hour power reserve from a single large, off-center barrel. This provides over four days of running autonomy. The performance targets are tight, with a stated accuracy of -3/+7 seconds per day, which is within chronometer-certified standards. Where the CMM.32 stands apart, especially for a tourbillon, is its durability claims. Yema specifies resistance to magnetic fields up to 2,000 Gauss and shock resistance up to 5,000 Gs. This is achieved using non-magnetic components, including a Swiss-made alloy hairspring and a Glucydur balance, along with Kif shock absorbers. The escapement uses components made via LiGA technology, a micro-manufacturing process designed to create parts with high precision and low friction. Any dialhead will appreciate the sapphire caseback, which reveals the CMM.32’s deep-blue finishing, constellation engravings, and a flame-blued ratchet wheel bearing a map of the Earth.

The Flying Tourbillon

At the 6 o'clock position is the flying tourbillon. Unlike a traditional tourbillon, which is secured by a bridge on both the top and bottom, a flying tourbillon is cantilevered, supported only from below. This construction creates the visual effect of the mechanism floating in space. Producing one requires exceptional balance and rigidity to compensate for the lack of an upper bridge. It’s a mark of high-horology that demands meticulous assembly and regulation to counteract gravity's effect on the escapement.

The Sidereal Time Display

The complication at 12 o’clock is what gives the watch its name, “Heure Sidérale” or Sidereal Time. The "celestial vault" disc on the dial completes one full rotation every 23 hours, 56 minutes, and 4 seconds. This is the length of one sidereal day—the time it takes for the Earth to rotate once relative to the fixed stars. This is fundamentally different from a standard 24-hour solar day. The display is designed to show the part of the night sky that is visible directly above the wearer at any given moment. It’s a direct, mechanical link to the astronomical observations that once set the standard for timekeeping in Besançon.

Case, Dial, and Lume Construction

The Spacegraf is housed in a 42mm Grade 5 titanium case measuring 12.15mm thick. The choice of titanium keeps the watch light, a practical consideration for a piece of this size and complexity. The case features a mix of finishes, with vertically brushed flanks and lugs against a circular-brushed bezel. Despite having a push-pull crown, the case is rated for 100 meters of water resistance. This is a robust figure for a watch with a flying tourbillon complication. The dial itself is deep black with a fine sandblasted grain and a PVD coating. The most interesting detail is how the luminescence is applied. Instead of paint, the hour markers are 3D blocks of solid Super-LumiNova BGW9 Grade X1. This treatment extends to the hands, numerals, tracks, and even the celestial disc, creating a striking luminous display in low light. The watch is fitted with a black leather strap that tapers from 21mm at the lugs to 16mm. It secures with a Grade 5 titanium pin buckle that matches the case finishing.

Positioning within Yema's Manufacture Lineup

This release demonstrates the upper range of Yema’s manufacturing capability. While our previous coverage looked at watches built around the brand's more accessible in-house calibers, like the micro-rotor in the Yema x Silberstein Marine 2 CMM.20, this Spacegraf operates in a different category. It shows a clear strategy of vertical integration across different price points. The CMM.32 shares a lineage with other manufacture movements from Morteau, but its complications place it at the pinnacle of the brand’s offerings. It builds on the same French-made philosophy seen in the Superman Bronze CMM.10, but scales it up to the level of high-horology. The Spacegraf is Yema's technical and historical showpiece.

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