Once neglected, the moon-phase display has become a totem of watch design.

“The two traditional moon-phase displays are either a crescent-shaped aperture or a simple round hole,” says Cartier’s head of movement development, Carole Forestier-Kasapi. “But in order to get new and creative, we have to get far away from what has been traditionally done.”

Forestier-Kasapi’s efforts with Cartier represent an industry-wide movement to rethink the moon-phase display, one of the oldest and most overlooked complications in watchmaking.

The moon phase, the first true astronomic complication, has moved in and out of favor with watch buyers since the late 19th century. But for all its emotional appeal, progressives in watchmaking today might contend that the moon-phase complication has languished—mechanically and aesthetically—since those days. The simple geared disk with 59 teeth remains easy enough to execute, but the error of producing an extra day every three years hardly supports the Swiss reputation for precision. Decoratively, the gold disk, perhaps decorated with a face on a sometimes-starred field of blue, became virtually ubiquitous.

Mechanically, the performance of moon-phase watches has improved across the industry in recent years. A handful of specialized watches have been endowed with extremely precise gear ratios possessing accuracies of nearly 1,000 years or more before a day’s error amasses. The bulk of high-end timepieces have extended their accuracy to a highly respectable 122 years with the addition of extra gear teeth to the lunar disk.

But for all these improvements, the most important changes have been aesthetic ones. Watchmakers like Forestier-Kasapi are giving the venerable moon phase a long-awaited face-lift. Her work with Cartier has included on-demand moon-phase displays as well as a seven-moon retrograde arc that presents all phases at once in waxing and waning positions.

The moon itself is one of the most obvious areas for cosmetic exploration. Arnold & Son maximizes this with a double, large-scale indication that takes up virtually the whole dial in its HM Double Hemisphere Perpetual Moon. The two moons, one each for the northern and southern hemispheres, are rendered in high relief in rose gold over a blue lacquer-over-guilloche background. Omega’s Speedmaster Moonphase Co-Axial Master Chronometer Chronograph possesses an essentially classical display, but the moon itself has been given a hyperrealistic treatment. A microfiche image is projected onto a coated sapphire disk that is then etched by a nanoscale laser. With the exception of the footprint that has been added in tribute to the model’s status as the “moon watch,” the display is a facsimile of an actual NASA photo.