- HumanitiesIT HAPPENED
- 4 de October de 2024
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The ten days that never existed. The Gregorian calendar

The ten days that never existed. The Gregorian calendar

October 4, 1582 was not followed by October 5, but by October 15. The reason for this anomaly was that Pope Gregory XIII decreed the change of the calendar in force until then, the Julian calendar, for a new one more in line with astronomical reality, which was named the Gregorian calendar in his honour. Thus, the year 1582 only had 355 days.
The Alexandrian Greek Eratosthenes had established in the 3rd century BC the length of a year at 365 days – the time it takes the Earth to complete an orbit around the Sun. Eratosthenes had also established a correction of one more day every four years, the leap years. It was called the Julian calendar because it was Julius Caesar who officially had adopted it in Rome in the 1st century BC for the entire Roman world. But it was not exactly like that either. Actually, the Earth takes a little less than 365.25 days to make a complete revolution around the Sun, approximately 365.242189 days.
In 325, the Council of Nicaea adapted the feasts of the liturgical calendar according to the astral moment in which Easter was to be celebrated, which is governed by the lunar calendar, and the rest of the movable feasts according to this. Easter was established on the first Sunday after the full moon following the spring equinox – in the northern hemisphere. That year the spring equinox coincided with March 21.
The time lag between 365.25 days and 365.242189 is about 11 minutes per year. It was imperceptible at first, but after 1257 years -from 325 to 1582-, ten days of “delay” had been accumulated. And according to the human calendar, the spring equinox was taking place ten days earlier than its astronomical occurrence. At the rate it was going and if it had not been corrected, in about 2500 more days we would be entering spring at the end of February… And a few thousands further on, Easter would have ended up coinciding with Christmas day.
Astronomers from the University of Salamanca had already warned of this discrepancy in 1515, and informed the Vatican, which ignored it. Again, in 1578, they informed the Holy See. After the second warning, a commission was created to study the issue, in which the astronomers Christopher Clavius, Luigi Lilio and Pedro Chacón stood out. It was also found that in the Alfonsine Tables – the first astronomical tables drawn up in Western Europe – drawn up in the 13th century on the initiative of Alfonso X the Wise, the tropical year had been assigned a value of 365 days, 5 hours, 49 minutes and 16 seconds. A Compendium was drawn up and on September 14, 1580, the calendar reform was approved, which would be put into practice two years later: October 5, 1582 was to be the 15th of the same month.
As a correction of the error that had caused the discrepancy, it was established that years that were multiples of 4 that were also multiples of 100 would not be leap years, with the exception of those that were also multiples of 400, which would be. Thus, the years 1700, 1800 and 1900 were not leap years, but 1600, 2000 and 2400 they were.
The first countries to adopt the Gregorian calendar were those of the Catholic world: the Holy See, Spain and the Italian principalities and states; France adopted it on December 9 of the same year. In 1583, the Catholic German states and the Netherlands (only the Catholic ones) adopted it. England followed suit almost two centuries later, in 1752. Others took even longer: China in 1912, Russia in 1918, Greece in 1923…
Despite its undoubted advantages over the Julian, the Gregorian calendar is not 100% accurate either. It adjusts the year to 365.2425 days, leaving a difference of 0.000300926 days, or about 20 seconds each year, which means that an adjustment is required every 3,300 years. If we take into account that there are 1,272 years left until that time, we should not be too worried. In any case, it is considered excessively complicated to try to create a rule to correct this discrepancy, also because the Earth slows down in its rotation and translation movements, which introduces a new time difference that would have to be corrected. So the most practical thing seems to be that anytime the time lag reaches one day – in a few thousand years – an additional leap year should be established only once… Or by then, let them do whatever they want; it is also not out of the question that, as it sometimes seems we’re pointing to, the flat-earthers may be in charge by then.
Source: educational EVIDENCE
Rights: Creative Commons