With the launch of its Executive Moonstruck Worldtimer ? a pair of limited editions in platinum and rose gold ? Ulysse Nardin lays claim to the only watch that depicts the motion of the moon and sun in relation to the Earth as well as a map of the tides. Here is what you need to know about this groundbreaking astronomical timekeeper.

Housed in a 46-mm case, and under a nonreflective sapphire crystal, the dial of the Ulysse Nardin Executive Moonstruck Worldtimer depicts in its center a map of the Northern Hemisphere as seen from the North Pole. This fixed map is circumnavigated by three concentric disks ? the outermost disk, bearing a symbol representing the sun, completes one revolution every 24 hours, sweeping over a display of 24 time zones divided into day and night sectors (with London, representing Greenwich Mean Time, at 6 o’clock). This solar disk controls the world-time function, which allows the wearer to read the time simultaneously in all 24 cities indicated on the dial’s flange. The moon’s orbit is displayed on the two inner disks, which work together. The top disk acts as a circular window showing the moon’s position, while the other, gold disk displays the moon’s changing phases. Ulysse Nardin’s innovative use of two rotating parts for this indicator has achieved an exceptionally high level of precision for it: the time lag for each lunar month is just 5.7 seconds per day, or just one day every 40 years.

The Moonstruck Wor...