Gregorian calendar is a solar calendar introduced at the end of the 16th century. This new calendar was calculated at the request of Pope Gregory XIII to fill the inaccuracies of the calendar in force which was the Julian calendar.

The Gregorian calendar has removed three leap years every 400 years. Thus all the secular years, ending with “00”, are no longer leap years except the years that can be divided by 400. So for example the years 2100, 2200, 2300, 2500, 2600 will not be leap years and the years 2400, 2800, 3200 will be leap years.

To correct the delay accumulated by the previous calendars it was decided to go directly from Thursday, October 4, 1582 to Friday, October 15, 1582. The new calendar was largely introduced at this time in the Catholic regions. It took several decades to be introduced in other regions, such as Protestant ones.