October 4 1582 CE – Pope Gregory XIII’s Calendar Becomes Official

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Though it may seem difficult to contemplate, the current layout of the international calendar is a fairly recent invention. Six months after it debuted in the Inter gravissimas papal bull, Pope Gregory XIII officially instituted a corrected calendar in Catholic territories on October 4, 1582. Due to the discrepancies of the Julian calendar, the following day in countries like Portugal and Spain was the 15th instead of the 5th. The problem with the system introduced by Julius Caesar in 46 BCE, according to Gregory and his fellow leaders of the Catholic Church, had to do with a slight miscalculation that built up over time. According to the former Roman Emperor’s calendar, the year lasted 365 days and 6 hours. By using advances in astronomy that had occurred in the intervening centuries, the Catholics learned the time frame was actually 11 minutes shorter. Insignificant during any one year, it added up to an additional 10 days’ worth of difference between where the vernal equinox should have been and where it showed up. Hoping to create a more uniform calculation for the annual Easter celebrations, Gregory had been forced to accept the edict issued by the Council of Trent to honor the Council of Nicaea’s decree that Easter should be Celebrated on the same day by all Christian churches. Aiming ensure the Church operated as close as possible to the standards set up by its forefathers — despite the fact it would be ignored by Protestant and Orthodox sects — Gregory employed dozens of experts as advisors. Using an approximation of 365.2425 days between each vernal equinox (mere seconds off the actual amount), the team working on a solution to the problem of “calendar drift” away from March 21st as the vernal equinox solved the issue of time lost to the Julian method. Ten days would have to be removed from the calendar. Though an elegant solution, it didn’t fully account for a miniscule 48 seconds’ worth of difference that would slowly add up, just like the 11 minutes had before. To compensate for this tiny mathematical issue, Aloysius Lilius proposed three less leap years for every 400-year period. Gregory agreed, allowing February 29th to be added only during years that turned over a new century if they were also divisible by 100 — the year 2000 had one but 2100 will not, for example. After announcing the change in February, the Papal States and four other nations put the new calendar into effect at midnight on October 4, 1582. The agreed-upon international calendar today, it took almost 450 years for the rest of Europe and much of Asia to adopt the changed format, sometimes using it in tandem with calendars based on religious or national traditions. Among the handful of exceptions who have not adopted the Gregorian version in any form, Saudi Arabia, Ethiopia, Nepal, Iran and Afghanistan are the most notable. Also On This Day: 1535 – The Coverdale Bible, the first English-language translation of Christianity’s sacred text, is printed 1795 – Napoleon Bonaparte comes to fame by suppressing a riot outside the French National Convention with cannons — a “Whiff of Grapeshot” 1830 – The Kingdom of Belgium separates from the Netherlands 1957 – The Soviet Union launches Sputnik 1 into space 1992 – A 16-year civil war in Mozambique comes to a close with the Rome General Peace Accords