Dictionary term
Epact
Direct answer
Epact: The Epact is a calendar number representing the Moon approximate age at a reference date, used especially in ecclesiastical lunar calculations.
The Epact is a computus value used to track the calendar Moon age.
The Epact is a computus value used to track the calendar Moon age.
A cycle or timeline schematic for comparing the named timekeeping concept.Quick reference
- Use when
- Use Epact when explaining historical computus, ecclesiastical new moons, and Gregorian Easter tables.
- Do not use it for
- Do not treat an epact as a direct modern observation of the Moon exact illuminated phase.
- Reference category
- Calendars & Timekeeping
- Related terms
- Intercalary Month, Golden Number, Calendar, Julian Date
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The story behind Epact
Medieval and Gregorian computists refined epact tables to reconcile lunar cycles with changing solar calendar rules.
Epact in spiritual tradition
Spiritually, the epact shows devotion working through disciplined arithmetic rather than secret lunar messages.
Epact: fact and faith, kept distinct
This is a factual calendar, astronomy, Earth-science, cultural-history, or observational reference. It can support wonder and practical planning without becoming a claim of fate, spiritual causation, or private revelation.
Epact in numerology
Epact is not a numerology claim. Any numbers attached to it should retain their ordinary scientific, calendrical, navigational, or historical meaning unless a separate symbolic interpretation is clearly labeled.
Why Epact matters
Epacts help coordinate lunar phase tables with solar calendar dates when calculating moveable feasts.
Epact at work: an example
An annual epact can guide a table to the ecclesiastical full moon used in an Easter calculation.
Where interpretation stops
Epact is presented as sourced astronomy, calendrical, Earth-science, cultural, or instrument-history reference. Definitions should distinguish measured phenomena from civil convention and historical interpretation, preserve location and time dependencies, and avoid turning factual sky data into a deterministic personal claim.
Sources and editorial method
Research references used for this entry include:
- 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
- Also appears in
- Calendars & Timekeeping
- Aliases
- None listed
- Last updated
- 2026-07-16
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Common questions
What is Epact?
The Epact is a calendar number representing the Moon approximate age at a reference date, used especially in ecclesiastical lunar calculations.
How is Epact used in an almanac?
Use Epact when explaining historical computus, ecclesiastical new moons, and Gregorian Easter tables.
What should I avoid when interpreting Epact?
Do not treat an epact as a direct modern observation of the Moon exact illuminated phase.
