Change From Julian to Gregorian Calendar
The Gregorian calendar was first introduced in 1582, but it took more than 300 years for all the different countries to change from the Julian Calendar.
Skipped Several Days
The papal bull issued by Pope Gregory XIII in 1582, decreed that 10 days be dropped when switching to the Gregorian Calendar. However, the later the switch occurred, the more days had to be omitted. (See table below).
This created short months with only 18 days and odd dates like February 30 during the year of the changeover.
In North America, the month of September 1752 was exceptionally short, skipping 11 days.
Switch Took More Than 300 Years
The Gregorian Calendar was first introduced in 1582 in some European countries (*). However, many countries used the Julian Calendar much longer. Turkey was the last country to officially switch to the new system on January 1, 1927.