What does lunation mean?
A lunation is the complete cycle of the moon’s phases from one new moon to the next, lasting approximately 29.5 days. The term is especially useful in astronomy and calendar history because it describes a lunar unit of time rather than the conventional calendar month, whose length is determined by the division of the year into months. Although a lunation is often called a synodic month, it differs slightly from the sidereal month, which measures the moon’s orbit relative to the stars. The word is relatively uncommon in everyday conversation, but it is valuable when discussing lunar calendars, traditional timekeeping, and the relationship between the moon’s phases and human schedules. A lunation is also sometimes used more broadly to mean a lunar month.
nounThe interval between one new moon and the next, approximately 29.5 days. It is also known as the synodic month.
- The period from one new moon to the next, approximately 29.5 days.
- A lunar month, especially in historical or astronomical usage.
"The next lunation begins when the moon reaches conjunction with the sun."
"Astronomers recorded the beginning of a new lunation from the observatory."
"The festival was timed according to the lunation rather than the solar calendar."
Plural lunations is used when referring to multiple lunar cycles or to successive intervals between new moons.
"The record includes the dates of several lunations."
A lunation is not the calendar month: it follows the moon’s changing phases and lasts about 29.5 days, making it slightly longer than most calendar months.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does lunation come from?
Lunation derives from Latin lunatio, a word associated with luna, meaning “moon.” The suffix -ation forms a noun indicating an action, process, or resulting period. The term entered English through astronomical and calendrical usage, where it referred to the period of the moon’s phases.
Related word forms
How lunation is actually used
Lunation is a formal or technical term, used chiefly in astronomy, chronology, and discussions of lunar calendars. It is less common in everyday speech than month.