Six and a half million Britons(or Britishers) went to bed on September 2, 1752, and woke up on September 14. The reason? The Calendar (New Style) Act of 1750, was the reason behind missing eleven days.
In 1582, Pope Gregory XIII was 10 years into his reign as leader of the Catholic church. He had a problem with Easter. The Julian calendar that the church (and large swaths of the world) used at the time measured a year as 365 days and 6 hours long. That’s close, but not quite right.
The average length of a year is 365 days, 5 hours and 49 minutes. The 11 minutes difference might not seem like all that much, but compounded over 1300 years, it begins to add up. So on February 24, 1582, Pope Gregory XIII released a papal bull—a declaration from the leader of the Catholic church—decreeing that those under the dominionship of his church would have to skip some days. Spain, large parts of Italy (which was not yet unified), the Netherlands, France, Portugal, Luxembourg, and Poland and Lithuania (who were at the time tied under a commonwealth) all adopted Gregory’s bull that year.
With the establishment of the Gregorian calendar or the Western calendar in October 1582, the world came to know of a timekeeping method that included a year having 12 months with 30 or 31 days in each month except for February. The world switched from Julian calendar to the Gregorian calendar because the former did not effectively translate the time the moon took to complete one revolution around the earth. The fault in the Julian calendar was spotted years later that it erroneously ignored the addition of 11 minutes of the solar year. Thereby reducing one day from the calendar after every 128 days. The Gregorian calendar did not have this mistake and it was running 11 days ahead of the Julian calendar.
Many countries during that time were debating over which of the two calendars they should follow. Switching from the Julian calendar to the Gregorian calendar was a daunting task. Some countries did it instantly. Some did it after a few years, while many countries hesitated altogether.
A strange occurrence, therefore, shocked the world on September 2, 1752. Where countries including France and Norway did adopt the Gregorian calendar in 1582 and 1700 respectively. England and America (present day USA) followed the change in 1752. According to the Julian calendar, May 25 was the New Year’s Day.
The difference in days between the formerly followed Julian calendar and the newly adopted Gregorian calendar kept going until September 1752. Then it was decided by England and America, following the Julian calendar at that time, to align them with the Gregorian calendar. As per the decision of the King of England, George II, September 2, 1752, was to be the last day of the Julian calendar and that the Gregorian calendar will be in effect from the next day.
However, that was not the case. As there was already an 11-day difference, the day following September 2, 1752, was not September 3, 1752, but in fact September 14, 1752.