Mondzeit (Moon Time) is a work based on the study of the 28 phases of the Moon, conforming a calendar that includes the original name of each phase in Latin, and the corresponding day date for each month through a system of interchangeable magnetic numbers. It consists of 28 spherical glass bottles, forming a linear array disposed in a metal shelf illuminated by dimmable LED. The bottles are filled with water to enhance the optical effect of their spherical format. From a formal point of view, it is related to my previous research on series and images, and perception through optical devices for dynamic transformation. In this case, the sequence of phases allows appreciating the Moon essentially as a dual phenomenon that links light and darkness in a rhythm of cyclic transformations. In more essential terms, the work seeks to put in value immemorial archetypal concepts, with certain universal validity, related to the cycles of life, the seasons, the passage of time and the importance of nature as an essential foundation of our life.