In the calendar ofiPhone 10 days left in the month of October 1582from October 4th we move directly to October 15th: the days in between seem to have never existed, but why? And no, this is not an error of Apple programmers. What happened is that in that period, in Italy and in a few other countries, the Julian calendar it was replaced by the current one Gregorian calendarand this led to “skipping” some days of October. If you have an iPhone, by opening the calendar app you can go back to that date and verify this curious fact.
Before October 1582 the Julian calendar which included 1 leap year of 366 days, alternating with 3 years of 365 days. This is because it was estimated that the solar year, i.e. the time it takes the Earth to make a complete revolution around the Sun, was 365.25 days, and therefore to “recover” the day lost due to that 0.25, a leap year was added every 4 years.
However, the Earth does not take exactly 365.25 days to go around the Sun, but slightly less, i.e. 365.2422 days. This means that, by adding leap years every 4 years, a discrepancy was created between the solar year and the Julian Calendar, thus leading to the “shifting” of the seasons. In fact, since the calendar was further ahead than the actual revolution of the Earth, at a certain point we found ourselves having, for example, the month of April while the Earth was still in the position relating to winter. This small difference, in the approximately 1600 years in which the Julian calendar has been in use, it has meant that the starting dates of the seasons have slowly moved, and with them the date for the celebration of Easter. To overcome this shift in the liturgical calendar, Pope Gregory XIII established a Calendar Commission which, on the proposal of Luigi Lilio, developed the Gregorian calendar.
The Gregorian calendar reduces the number of leap years and establishes that
all years divisible by 4, such as 2024 and 2028, are leap years, with the exception of years divisible by 100 but not by 400, so 1700, 1800 and 1900 are not leap years, while 1600, 2000, and 2400 are.
Thanks to this reduction in the number of leap years, the average duration of a year becomes 365.2425 days, which differs very little from the 365.2422 days of the solar year. In this way the slippage of the dates has been greatly reduced so much so that we can expect a slippage of the dates by one day once every 3123 years.
But why did all this lead to the loss of 10 days of the calendar? The fact is that when the Gregorian calendar the dates had already shifted by a few days compared to the seasons, and to compensate for this shift yes established that the date after 4 October 1582 was 15 October 1582. In this way the spring equinox, on which the date of the celebration of Easter was based, returned to occur on March 21st, as it still happens today.
A curious fact is that not all countries in the world, or even in Europe, immediately adopted the Gregorian Calendar, for example in England it was only adopted in 1750, for this reason when the English army faced the French army on King’s Island on 12 July 1627, for the French it was actually 22 July: the battle was therefore fought by the two armies on two different dates, but on the same day.
In more recent times, at London Olympics of 1908the start of the competition was scheduled for July 10th, but the Russian team did not show up on time despite having traveled to London a few days in advance. The fact is that July 10th for the Russians, who did not use the Gregorian calendar, coincided with July 23rd of the Gregorian calendar, the one to which the Olympics program referred.
