calendar

Introduction
Measurement of time and types of calendars
- Standard units and cycles
- Time determination by stars, Sun, and Moon
- Complex cycles
Ancient and religious calendar systems
- The Near East and the Middle East
  - Babylonian calendars
  - Other calendars used in the ancient Near East
    - The Assyrians and the Hittites
    - Iran
  - The Egyptian calendar
  - Ancient Greek calendars in relation to the Middle East
    - Earliest sources
    - The year
    - Months, days, seasons
  - The early Roman calendar
  - The Jewish calendar
    - The calendar in Jewish history
    - The structure of the calendar
    - Months and important days
  - The Muslim calendar
- The Far East
  - The Hindu calendar
    - Early history
    - The classical calendar
    - The sacred calendar
    - The eras
  - The Chinese calendar
- The Americas
  - The Mayan calendar
  - The Mexican (Aztec) calendar
  - Peru: the Inca calendar
  - North American Indian time counts
The Western calendar and calendar reforms
- The Julian calendar
- The Gregorian calendar
  - The date of Easter
  - Adoption in various countries
- Calendar reform since the mid-18th century
  - The French republican calendar
  - Soviet calendar reforms
  - Modern schemes for reform

References & Edit History Related Topics

Images, Videos & Interactives

Kalendarium (“Calendar”) by Regiomontanus

Infographic showing date formats: Day-Month-Year (most of world), Year-Month-Day (China, Japan, etc.), and Month-Day-Year (United States).

calendar section of Les Très Riches Heures du duc de Berry

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Calendar conversion

Aerial view of Stonehenge stone circle with large upright and fallen stones arranged on green grass.

The cycle of the Jewish religious year

Chinese calendar from the 18th century

Chinese yinyang li calendar

Aztec calendar stone

For Students

perpetual calendar

calendar summary

calendar: Related Content

Written and fact-checked by The Information Architects of Encyclopaedia Britannica

Photos and Videos

Kalendarium (“Calendar”) by Regiomontanus

Infographic showing date formats: Day-Month-Year (most of world), Year-Month-Day (China, Japan, etc.), and Month-Day-Year (United States).

calendar section of Les Très Riches Heures du duc de Berry

Aerial view of Stonehenge stone circle with large upright and fallen stones arranged on green grass.

The cycle of the Jewish religious year

Chinese calendar from the 18th century

Chinese yinyang li calendar

Aztec calendar stone

Felipe Guamán Poma de Ayala: El primer nueva corónica y buen gobierno, depiction of an Inca bookkeeper using a quipu

Kiowa calendar painting

What is Leap Day?

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Topics

date Inca calendar sacred calendar world calendar lunisolar calendar International Fixed Calendar Our Days Are Numbered: 7 Crazy Facts About Calendars Advent calendar French republican calendar Gregorian calendar clock sundial chronometer chronograph gnomon clepsydra hourglass 22 Questions About Time and Timekeeping Answered dynamical time Standard Time

Dig Deeper: More Articles That Discuss This Topic

time: Time units and calendar divisions

Key People

How did Ptolemy explain retrograde motion?

Ptolemy

Egyptian astronomer, mathematician, and geographer

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Dionysius Exiguus

canonist