Calendars and time
Metonic Cycle
Direct answer
Metonic Cycle: The Metonic Cycle is a period of 19 solar years that is close to 235 synodic months, allowing lunar phases to recur near the same calendar dates.
The Metonic Cycle approximately matches 19 years with 235 lunar months.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Golden Number, Callippic Cycle, Calendar, Julian Date
The Metonic Cycle approximately matches 19 years with 235 lunar months.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Metonic Cycle
The cycle is named for the fifth-century BCE Athenian astronomer Meton, though related nineteen-year knowledge appeared in earlier traditions.
Why Metonic Cycle matters
Metonic Cycle’s close fit provides a practical framework for leap months and ecclesiastical lunar tables.
Metonic Cycle in practice: an example
Seven leap months distributed through nineteen years can keep a lunisolar calendar broadly aligned with the seasons.
Where readings of Metonic Cycle go wrong
A common error is to call the cycle exact; phase times drift because 19 years and 235 lunations are not identical.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Astronomical Almanac Glossary - Reference definitions for astronomical periods, coordinates, dates, and time scales.
- U.S. Naval Observatory: Introduction to Calendars - Official overview of calendar systems, leap rules, eras, and historical calendar reform.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Compare solar years and lunations
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Common questions
What is the Metonic Cycle?
The Metonic Cycle is a period of 19 solar years that is close to 235 synodic months, allowing lunar phases to recur near the same calendar dates.
What does the name Metonic Cycle mean?
The cycle is named for the fifth-century BCE Athenian astronomer Meton, though related nineteen-year knowledge appeared in earlier traditions.
What do people get wrong about the Metonic Cycle?
A common error is to call the cycle exact; phase times drift because 19 years and 235 lunations are not identical.
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