Phone calendar is missing 10 days, but it's not because the iPhone is broken

An interesting "bug" was discovered on the iPhone calendar, when October 4, 1582 was followed by October 15. Photo: Apple Insider .

If you go into your smartphone calendar app or go back in time to 1582, you will see that October is missing 10 days. Right after Thursday, October 4 is Friday, October 15, 1582.

This is not a programming error or someone intentionally playing a joke, but in fact, these 10 days do not exist in the calendar at all. The reason lies in the change in the way people count days, months, and years in the 16th century.

At that time, Pope Gregory XIII presided over the Catholic Church, issued the decree "Inter gravissimas", officially promulgating the Gregorian calendar. Before that, the whole of Europe was still using the Julian calendar, established in 46 BC, under the instructions of Supreme Commander Julius Caesar.

These two calendars are quite similar. Both are solar calendars, consisting of 12 months with the number of days ranging from 28 to 31. The total number of days in a year is usually 365, and in certain years there is an extra leap day in February.

October 1582 on iPhone Calendar.

The main difference lies in how leap years are determined. The Julian calendar adds a day every four years, as does the Gregorian calendar, with the added condition that the year must be divisible by both 100 and 400. For example, the years 1900 and 2100 are divisible by 4 and 100, but not by 400, so they are not leap years.

To put it simply, the Julian calendar counts each year as having 365.25 days (1 leap day each year). However, the actual solar year (the time it takes for the Earth to revolve around the Sun) is only about 365.2422 days long.

This discrepancy (about 11 minutes per year) results in the Julian calendar being off by one day every 128 years relative to the solar cycle. While this may seem small, it is a big problem for the Catholic Church because it seriously disrupts the timing of Easter celebrations.

The Church decreed that Easter should be celebrated on the first Sunday after the first full moon after the vernal equinox, which was March 21. By the 16th century, this phenomenon had accumulated to the point that the vernal equinox fell on March 11, making the calendar for the holiday inaccurate.

Therefore, Pope Gregory XIII introduced the Gregorian calendar. In order to adjust the new calendar to the actual movement of the Sun, it was necessary to remove 10 days, the number of days that had accumulated due to errors in the Julian calendar.

October was chosen as the month to drop these days because it did not coincide with any major events in the Christian calendar. After the Feast of St. Francis of Assisi on October 4, the switch to the Gregorian calendar took place, and the world jumped straight to October 15.

Therefore, most calendars that look up the year 1582 will skip that period, including online calendars on iPhone.

Source: https://znews.vn/lich-dien-thoai-bi-thieu-mat-10-ngay-nhung-khong-phai-do-iphone-hong-post1554288.html