Calendars and time
Synodic Month
Direct answer
Synodic Month: A Synodic Month is the mean interval between identical lunar phases, such as one new moon and the next.
A Synodic Month is the approximately 29.53-day lunar phase cycle.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Draconic Year, Sidereal Month, Calendar, Julian Date
A Synodic Month is the approximately 29.53-day lunar phase cycle.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Synodic Month
Month systems began from observed phase cycles long before the orbit was described mathematically.
Why Synodic Month matters
Synodic Month is the lunar period most directly connected with visible phases and the month lengths of lunar calendars.
How to read Synodic Month
Synodic Month speaks to phase recurrence, lunation numbering, lunar calendars, and spring-neap tide timing.
Synodic Month in practice: an example
A full moon recurs about 29.53 days after the previous full moon, though individual lunations vary.
Where readings of Synodic Month go wrong
It is a mistake to substitute 28 days for the synodic month or assume every lunation has the mean length.
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.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Track the phase-to-phase cycle
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More in Calendars & Timekeeping
- Week Number
- Barycentric Dynamical Time
- Common Era
- Dynamical Time
- Greenwich Sidereal Time
- Julian Century
- Lunisolar Calendar
- Reduced Julian Date
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Common questions
What is a Synodic Month?
A Synodic Month is the mean interval between identical lunar phases, such as one new moon and the next.
What do people get wrong about a Synodic Month?
It is a mistake to substitute 28 days for the synodic month or assume every lunation has the mean length.
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