Calendars and time
Gregorian Calendar
Direct answer
Gregorian Calendar: The Gregorian Calendar is the solar civil calendar introduced in 1582 that uses a refined leap-year rule to keep calendar dates close to the seasonal year.
The Gregorian Calendar is today's widely used civil calendar with a 400-year leap-year rule.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Calendar, Solar Calendar, Lunar Calendar, Lunisolar Calendar
The Gregorian Calendar is today's widely used civil calendar with a 400-year leap-year rule.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Gregorian Calendar
Pope Gregory XIII introduced the reform in 1582; adoption then spread gradually rather than occurring worldwide on one date.
Why Gregorian Calendar matters
Gregorian Calendar is the default calendar for most modern almanac dates, but historical adoption varied by country and community.
How to read Gregorian Calendar
Gregorian Calendar explicitly speaks to modern dates and when converting records from Julian or other systems.
Gregorian Calendar in practice: an example
Years divisible by 100 are not Gregorian leap years unless they are also divisible by 400, so 2000 was a leap year but 1900 was not.
Where readings of Gregorian Calendar go wrong
It is a mistake to project Gregorian dates backward without labeling them proleptic or ignore regional adoption history.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Introduction to Calendars - Calendar definitions and the astronomical basis of solar, lunar, lunisolar, Julian, and Gregorian systems.
- U.S. Naval Observatory: Astronomical Almanac Glossary - Reference definitions for astronomical coordinates, events, calendars, and time scales.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
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Common questions
What is the Gregorian Calendar?
The Gregorian Calendar is the solar civil calendar introduced in 1582 that uses a refined leap-year rule to keep calendar dates close to the seasonal year.
What do people get wrong about the Gregorian Calendar?
It is a mistake to project Gregorian dates backward without labeling them proleptic or ignore regional adoption history.
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