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Accurate to 99.998 per cent The moon-phase display

Moon-phase display in the "raw" state before completion of a watch

Since the dawn of humanity, people have been looking to a very special celestial body when it comes to measuring periods of time: the moon. Its regular rhythm can be easily tracked, and for thousands of years, it has been the foundation on which our calendar is subdivided into weeks and months. A. Lange & Söhne’s watchmakers are also fascinated by the earth’s satellite. To such a degree, in fact, that they leverage all the potentials of mechanical precision to emulate its orbit with extreme accuracy and reproduce its radiance as brilliantly as possible. 

Several concepts for displaying the moon phases

Precision in detail


Most of our moon-phase displays are 99.998 per cent accurate, so if the watch runs without interruption, a correction by one day is only needed when 122.6 years have elapsed. This is achieved with an ingenious mechanical transmission that steps down the rotation of the hour wheel. But Lange’s product developers have demonstrated that precision can be further enhanced: The mechanism of the patented orbital moon-phase display of the RICHARD LANGE PERPETUAL CALENDAR “Terraluna” is calculated with such accuracy that if the watch runs without interruption, it will take 1058 years before a correction by one day is required.

The mechanism of the moon-phase display

Bright brilliance


The rich blue hue is another special facet of Lange lunar discs. The unique chromatic effect is achieved by superposing light waves. To produce this so-called interference phenomenon, Lange has partnered with scientists to develop a patented coating process for the solid-gold discs. The vibrant blue tint forms a remarkably high-contrast backdrop for the stars. In the RICHARD LANGE PERPETUAL CALENDAR “Terraluna”, more than two thousand stars in five different sizes emphasise the fascination of the night sky.

A moon for days and nights


Presented in 2016, the newly conceived moon-phase display of the LANGE 1 MOON PHASE with a day/night indicator always presents the moon against a realistic depiction of the sky. This is achieved with a two-part design. A celestial disc that rotates clockwise once every 24 hours forms the backdrop for the lunar orbit. On the celestial disc, the different times of day are represented by varying blue hues based on interference effects. During the day, the sky is bright blue without stars, but gradually becomes darker as the afternoon progresses. At night, the sky is dark blue and studded with a multitude of stars.

The moon-phase mechanism of the LANGE 1 MOON PHASE

The orbital moon-phase display


In the RICHARD LANGE PERPETUAL CALENDAR “Terraluna”, the depiction of the moon phases also by far transcends the classic notion of precision by incorporating the surroundings of the earth’s companion. The patented orbital moon-phase display shows the current moon phase as well as the positions of the moon and sun as an observer in the northern hemisphere would see them. The display is composed of the celestial disc, the lunar disc which lies beneath it, and the earth disc in the centre. The position of the sun is defined by the balance. The moon can be seen through a round aperture in the celestial disc. It orbits the earth once in the anti-clockwise direction in slightly more than 29.5 days. A gear train assures that the moon phase is always accurately rendered.
In the centre of the celestial disc, the earth disc rotates through 360 degrees once a day. It is daytime on the half that faces the sun (the balance) and nighttime on the other. The circumferential 24-hour scale provides a time-of-day reference for regions in the northern hemisphere.

Astronomical complication: the orbital moon-phase display

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