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“It is pleasant for an old man to be able to go to bed on September 2, and not have to get up until September 14.” - Benjamin Franklin on England adopting the Gregorian Calendar.
Today is the 436th anniversary of the first adoption of the Gregorian Calendar! So, in our first #TBT this year the Watson will take a closer look at this historical event.
The average solar year in the Julian Calendar has 365.25 days, and the addition of a leap day every four years was meant to keep the calendar and the seasons in sync. This seemed to work for centuries, but there was slight inaccuracy in the measurement of the solar day which amounted to the calendar dates of the seasons to move back almost one day per century. This problem persistent for centuries which ended being an interesting predicament for the Catholic Church in the 1500s.
Pope Gregory XIII wanted Easter to fall on the vernal equinox as it did in 325 during the Council of Nicaea. This discrepancy between the Julian Calendar and the actual solar needed to be adequately addressed before he could meet his goals.
He employed the assistance of many notable astronomers and mathematicians of the day including Christopher Clavius, a German Jesuit and Mathematician, in correcting the faulty math of the Julian calendar implemented by Julius Caesar in 46. The new Gregorian calendar was introduced in the papal bull Inter gravissimas and advanced the date by 10 days. Which meant that in 1582 that October 4th was followed by October 15th. October 4th of that year is widely considered the first adoption of the Calendar, but an argument could be made for other days in 1582. He also introduced an intricate method of calculating leap years. In the Gregorian calendar, no century year is a leap year unless it is exactly divisible by 400, including years like 1600 and 2000.
It was adopted rather quickly by the Italian states, Portugal, Spain, and the German Catholic states. Over time it was adopted by other states. Protestant German states adopted the Gregorian Calendar in 1699; England and its colonies in 1752, and Sweden quickly followed in 1753. Other notable adoptions include Japan in 1873, China in 1912, the Soviet Union/Russia in 1918, and Greece in 1923.
Gregory XIII was born Ugo Boncompagni on June 7, 1502, in Bologna. He was Pope from 1572 to his death in 1585. He is most widely known for introducing the Gregorian Calendar, but he was famous, or rather infamous, for numerous other reasons.
Most notably among these is his reaction to the Massacre of St. Bartholomew’s Day. This was the slaughter of Huguenots, a local protestant sect, that began in Paris in the summer 1572 and quickly spread throughout France. He rejoiced at their deaths and celebrated the massacre with a Te Deum, a special hymn, in Rome.
Despite the ingenious calculations that went into the calendar, it is still off by 26 seconds. So, since 1582 a discrepancy of several hours has developed. This means that in 4909, the Gregorian calendar will be a full day ahead of the solar year. This might mean that some futuristic space pope will get to plant their name on a new Calendar, but it is more likely that humans will find some better, universal means of measuring the solar year.