Worldwide Calendar Systems

Julian, Gregorian, Jewish, Islamic, Hindu, Buddhist, Chinese, Mayan and Aztec, Baha'i, and Zoroastrian calendar systems are all used throughout the world. 

A calendar is a tool for keeping track of time using divisions such as days, weeks, months, and years. 

  • Some of these categories, such as months, are derived from observations of natural occurrences. 
  • Others, like as weeks, are completely random. 
  • People used to count by moon cycles (months), but when a more practical, shorter period was required, days were grouped, for example, the intervals between market days likely led to the adoption of the seven-day week. 

Beginning in the third century B.C., the traditionally Jewish seven-day week became a norm across Western culture. 


  • Despite the fact that the amount of daylight varies throughout the year, the day is a pretty natural divide. 
  • The Babylonians divided the day into twenty-four hours, although the hours fluctuated in length over the year. 
  • The day was first given scientific regularity with the invention of precise clocks, which was a consequence of the Renaissance's concern in nautical navigation. 


  • A lunar month, or the length of a complete cycle of the moon's phases, lasts approximately 29.5 days, is easily recognized by all, is short enough to be counted without large numbers.
  • A lunar month closely corresponds to the female menstrual cycle and, given its relationship to the tidal cycle, the duration of cyclic behavior in some marine animals. 

  • Its importance stemmed from its simplicity and ease of observation (assuming overcast skies are excluded), and it was extensively adopted as the foundation for calendars in many civilizations. 
  • The duration of each month varied depending on the culture; for example, the Babylonians alternated between twenty-nine and thirty-day months, while the Egyptians kept them at thirty days. 


  • The issue with using a lunar calendar is that the seasons are determined by the sun's cycles, not the moon's, and the predictability of the seasons is critical to agricultural productivity. 
  • Solar observation, either by monitoring the cycle of the midday shadow produced by a stick put vertically in the ground, or by complex astronomical calculations, may be used to predict the seasons. 
  • Both systems produced a solar year of around 365 days, which was incompatible with the twelve 29.5-day lunar months, which produced a 354-day year. In various ways, civilizations tried to harmonize lunar months with the solar year. 

The most important ancient effort was that of Egyptian astronomers, who set up the Roman calendar that Julius Caesar adopted, based on accurate mathematical measurements and drawing from Babylonian astronomy.

You may also want to learn more about Global Calendar Systems here.