What is Time? Summary of Calendars, Jake Jackson's These Fantastic Worlds

What is Time? Quick Summary of Calendars in History

Calendars have been created and re-formed by civilisations such as the ancient Egyptians, individual events like the French Revolution and religions like Islam. All such calendars are based on the observations of natural year cycles.

Ancient Egypt

A 365-year day was used from at least 4000 bc, divided into 12 months of 30 days, plus five extra days. Three groups of four months followed the flooding, growing and harvesting seasons of the Nile. As there were no leap years, New Year’s Day moved throughout the seasons over a 1460-year cycle (and reflected in celestial decorations in Pharaonic tombs). The adoption of the Julian calendar in 26 BCE saw some slight variations, including the new leap days added at the end of the Egyptian year: 29 August of the Julian calendar.

Drawing of Astronomical Ceiling, Tomb of Senenmut c 1500 BCE

Extract of a drawing from the Astronomical ceiling in the Tomb of Senenmut, dated approx. 1500 BCE.

Ancient Greece

A number of different systems were used, all attempting to reconcile the observable differences between the solar and lunar years. Before 1000 bc, a lunar year with erratic intercalation to bring it into line with the solar year was eventually superseded by more systematic octaeteris, an eight-year cycle with five years of 12 months followed by three years of 13 months. In the fifth century bc, the Athenian Meton discovered the cycle to which his name has been lent: the metonic cycle, a 19-year solar cycle of 235 lunar months. This cycle had been indepen­dently utilised by a number of cultures.

China

The Ancient Chinese, from at least as early as 2000 bc, used a combination of lunar and solar years, employing leap months to resolve the difference and, like a number of other cultures including the ancient Greeks, leading to independent adoption of what we now term the metonic cycle. Numbers were not used to mark the years, but 22 symbols of nature and cosmology (namely the Chinese zodiac) were combined to create 60-year periods, named after the first ruling emperor of the period. Modern China combines lunar and solar cycles to create a year of 24 two-week periods.

French Revolution

Lasting from 1793 to 1806, this calendar was divided into 12 months of 30 days. A 10-day period was called a decade and days were divided into units of 10 hours. New Year’s Day started on the autumn equinox.

Execution of Robespierre and his supporters in 1794, a year after the adoption of the Revolutionary Calendar.

Gregorian Calendar

A reform of the Julian calendar, this is based on a more accurate measurement of the solar year, 365.2425 days, and caused the removal of 10 days from the year of 1582 when it was initially introduced. It is now the de facto standard throughout the Western and diplomatic world.

India

Ancient India, with a cultural inheritance that included Babylonian, Sumerian, Vedic, Hindu and Buddhist influences could boast of almost every combination of lunar and solar calendars. Modern India uses the Gregorian calendar but New Year’s Day and the year count differ: the reformed Indian calendar was introduced on 22 March 1957 of the Gregorian calendar, corresponding to New Year’s Day of the historical Saka calendar, 1879.

Islamic Calendar

This lunar calendar started in ad 622 according to the Gregorian calendar, marking the date of Muhammad’s emigration to Medina. Known as the Hidjra, this event gives rise to acronym AH (After Hegirae) used after the date. The year is 354 days long with 12 months alternating between 29 and 30 days. Leap years occur 11 times in a cycle of 30 years and New Year’s Day, like the calendar of the ancient Egyptians, moves through the seasons during this cycle.

Jewish Calendar

The modern calendar was defined between the fourth and tenth centuries ad, with dates reaching back to 3761 bc, the beginning of the world as established by Jewish scholars of the period. The lunar calendar has a complicated intercalation which is designed to avoid leap days and months falling on feast days, Fridays and Saturdays. This gives ordinary years of 353, 354 and 355 days and leap years with 383, 384 and 385 days. New Year occurs during September.

Julian Calendar

Based on the solar year this lasts 365.25 days. The quarter of a day was accumulated over three years and added in the fourth. However, the true year was slightly shorter, which meant that the calendar was 11 minutes and 14 seconds too long. This inaccuracy lasted until 1581, by which time European mathematics could compute fractions smaller than a quarter and therefore make more precise predictions.

South and Central America

Aztec Wheel of Time

The Aztec Wheel of Time

Aztec and Mayan cultures were amongst the many who used two concurrent calendars, a ritual 260-day calendar of feasts and days of worship and a 360-day year with 18 months of 20 days each, plus five special days.


Over several posts on What is Time? we’ve taken a look at calendars, the next in the series introduces the many different types of clock from their invention and varied use throughout the world…


What is Time Links?

Some other links about Time