Mondmonat

Mondmonat (literally “Moon month”) is a term used to describe the time interval defined by the Moon’s cycle of phases, typically the period from one new moon to the next. It corresponds to what is commonly called a lunation, the natural cycle of lunar visibility as the Moon alternates from new to increasing illumination and back to new.

Duration is governed by the synodic month, averaging about 29.53 days. In practice, a Mondmonat can vary, with lengths roughly in the range of 29.2 to 29.9 days due to the elliptical shape of the Moon’s orbit and the Earth’s motion around the Sun. This differs from the sidereal month, which is about 27.32 days and measures the Moon’s orbital period relative to the fixed stars.

In calendars and timekeeping, the Mondmonat is often a concept rather than a fixed calendar unit. Lunar calendars may begin months with visible crescent moons or with new moons, and some systems assign months of 29 or 30 days irrespective of exact astronomical timing. In many today’s contexts, the term lunation is preferred in scientific usage, while Mondmonat appears mainly in historical or ethnographic German-language sources.

Etymology: Mondmonat is a compound of Mond (Moon) and Monat (month). It is a descriptive term for the Moon-based cycle rather than a distinct calendar system. See also lunation and synodic month for related concepts.