The ten days of history that never existed: when the calendar tore out ten pages at once

In 1582, the Western world went from October 4 to the 15th to adapt to the Gregorian calendar, which was more accurate than the previous one, the Julian, of Roman tradition.

It did not seem like a very relevant gap: just 11 minutes and 14 seconds seems very little in the times of Humanity. However, that was the extra time that the Julian calendar allowed for the length of a year. However, from the year 46 when Julius Caesar implanted this model until the year 1582 when it was decided to reform the almanac by decision of Pope Gregory XIII, Humanity had accumulated ten days in advance in the arrival of the seasons and in the celebration of certain festivities like Easter , for example, which was celebrated earlier and earlier. So it had to be fixed somehow. This is the story of the birth of the Gregorian Calendar and how Teresa de Jesús achieved one last miracle: a leap into the future ten days after her death.The days between October 5 and 15, 1582, 420 years ago today, did not exist, they were eliminated from history.

Julius Caesar had a correct idea: he replaced the lunar calendar to implant a solar one that established the length of the year at almost exactly what it is established today: 365.25 days. It contained months of 30 and 31 days, except February which had 28 days and 29 in leap years. But, despite the fact that the Greek astronomers already knew (Hipparchus had shown it, a century before the Julian reform) that the tropical year was a few minutes shorter than 365.25 days, the astronomer in charge of calculating the length of the year passed by 11 minutes and 14 seconds. The consequence of this gap is that the Julian calendar lost about one day every 130 years, three days every four centuries. After sixteen centuries, the gap was more than evident.

The solution

So, when Pope Gregory XIII was elected, he decided to solve the problem and commissioned various studies. One was carried out by the German Jesuit astronomer Christopher Clavius ​​and another by the University of Salamanca, the most important in the world in 1515. The astronomer Luigi Lilio (Aloysius Lilius) also made his contributions, but the definitive authorship is not clearly attributed. The solution to the problem was quite imaginative: it was a modification of the rule of leap years, which would continue to be every four years, but with two exceptions.The years that were divisible by 100 would not be leap years, but if they were divisible by 400 – for example 1600, 2000, 2400 – they would still be. In this way, the adjustment error of the astrological year and the year of our calendars was minimized: it would be only one in every 3,300 years. Enough time to eliminate a day, if the Earth maintains its speed of rotation and translation unchanged.

However, the time lag had to be fixed to produce the fit before starting with the new system. Pope Gregory decided that the days between the 5th and the 15th of 1582 were suppressed. They were erased from history. Interestingly, on October 4 of that year, Teresa de Jesús died, performing one last “miracle”: she was buried the next day, when it was already October 15.

The first countries to adopt the Gregorian calendar reform were those dependent on the Hispanic Monarchy, under the mandate of King Felipe II, the largest empire at that time, which was made up of Spain and its viceroyalties in America, the Philippine Islands, the states from Southern Italy and Portugal, then also under the Spanish Crown . Also the Italian states dependent on the Holy See in 1582. However, not in all parts of the world the calendar was advanced on the same dates. For example, in France , Lorraine, and the Mississippi, after Sunday, December 9, 1582, came Monday, December 20. Great Britain and its American colonies did not do so until 1752. Egypt passed from December 20, 1874 to January 1, 1875. Turkey changed from February 16 to March 1, 1917. Russia passed from February 1 to 14, 1918, already with Lenin in power.

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