The History of Calendars
Below is a MRR and PLR article in category Reference Education -> subcategory Science.
The History of Calendars
Orthodox Christians recognize Christmas on January 7, and their "Old New Year" follows a week later on January 14. This timing traces back to Julius Caesar's reforms...
In ancient Rome, the calendar was often misaligned due to neglect in adding an extra month every two years, as needed to reconcile the lunar calendar with the solar year. In 46 BC, Julius Caesar introduced the "Year of Confusion," extending the year to 445 days to correct the accumulated discrepancies over centuries.
Caesar established January 1 as the start of the New Year, aligning with the traditional convening of the Senate. He also adjusted the lengths of various months. This led to the formation of the Julian Calendar, which was inspired by the Aristarchus calendar from 239 BC. Following Caesar's assassination, the month of Quintilis was renamed July in his honor.
The Julian calendar approximated the solar year as 365 days and 6 hours, adding an extra day every fourth year to create a leap year of 366 days. However, this calculation was slightly off by 11 minutes and 14 seconds, resulting in a gradual shift. By 325 AD, the Spring Equinox was on March 21 instead of March 25.
The First Ecumenical Council in Nicea in 325 enshrined this misalignment by determining that Easter would be celebrated on the first Sunday after the first full moon following the Spring Equinox on March 21.
By 1582, the equinox was on March 11, causing concern. Efforts by Popes Paul III and Pius V to realign the calendar had little effect. Pope Gregory XIII, in his tenth year as pope, introduced a new reform. He decreed that 3 leap years would be skipped every 400 years, requiring a year divisible by 400 to have a leap day.
To align with this new system and return the equinox to March 21, ten days were omitted in October 1582. Thursday, October 4, was directly followed by Friday, October 15, leaving many in Europe feeling as though they had lost ten days.
Despite the uproar, the Gregorian calendar managed to stabilize the issue. By the 17th century, the Julian calendar saw the equinox shift to March 11, then progressively earlier in subsequent centuries. This spurred controversy in Protestant regions; Britain and its colonies adopted the Gregorian calendar in 1752, altering their New Year from March 25 to January 1 and skipping 11 days.
Other nations followed suit: Sweden in 1753, Japan in 1873, Egypt in 1875, Eastern Europe between 1912 and 1919, and Turkey in 1927. In Russia, revolutionaries in 1918 moved the date from January 31 to February 14, skipping 13 days.
In 1910, Pope Pius X shifted the ecclesiastical year's start from Christmas Day to January 1, effective from 1911 onward.
Meanwhile, the Orthodox Church continued using the Julian calendar. In 1923, a Conference of Orthodox Churches in Constantinople introduced a revised calendar, reducing the number of leap years every 900 years and creating a minute discrepancy with the solar year of just 2.2 seconds annually. This revision means the Spring Equinox regresses by one day every 40,000 years, requiring a 13-day adjustment to align back to March 21. This modification explains the difference between December 25 in the Gregorian calendar and January 7 in the revised Julian-Orthodox calendar.
You can find the original non-AI version of this article here: The History of Calendars.
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