Q: Moon phase or moon face? Which is correct?
A: Even experienced watch enthusiasts often confuse the terms moon phase and moon face. The correct term is moon phase, which indicates the age of the moon. Generally, a rotating moon disc with a picture of the moon rotates in approximately 29.5 days, indicating the approximate age of the moon.
In recent years, an increasing number of watches have been equipped with moon phase-like displays to indicate day and night. However, these displays only rotate once a day and do not indicate the age of the moon. It is therefore incorrect to call them moon phase displays.
Moon discs don't always equal moon phases
On the other hand, there are watches like the Ulysse Nardin Astrolabium Galileo Galilei, which tell the phase of the moon not with a moon disc but with two hands that indicate the positions of the sun and moon. Due to its structure, it looks different from a typical moon phase watch. However, functionally, this watch that tells the phase of the moon can be said to be equipped with a moon phase. A watch with a moon on it does not necessarily have a moon phase.
For more information on moon phases, see this article.
"The mechanism and evolution of the moon phase, and representative models'
