Did you know that nothing happened between 3 and 13 September 1752?
In September 1752 the Julian calendar was replaced with the Gregorian calendar in Great Britain and its American colonies. The Julian calendar was 11 days behind the Gregorian calendar, so 14 September got to follow 2 September on the day of the change. The result was that between 3 and 13 September, absolutely nothing happened!
The calendar switch also influenced the way George Washington's birthday is celebrated. He was born on 11 February 1731, but the anniversary of his birth is on 22 February because of the 11 days eliminated from the calendar switch. At the same time, New Year's Day was changed from 25 March to 1 January, thus according to the new calendar, Washington was born in 1732.
The first Roman Calendar (introduced in 535BC) had 10 months, with 304 days in a year that began in March. January and February were added only later. In 46BC, Julius Caesar created "The Year of Confusion" by adding 80 days to the year making it 445 days long to bring the calendar back in step with the seasons. The solar year - with the value of 365 days and 6 hours - was made the basis of the calendar. To take care of the 6 hours, every 4th year was made a 366-day year. It was then that Caesar decreed that the year begins with the 1st of January.
In 325AD Constantine the Great, the first Christian Roman emperor, introduced Sunday as a holy day in a new 7-day week. He also introduced movable (Easter) and immovable feasts (Christmas).
In 1545 the Council of Trent authorised Pope Paul III to reform the calendar once more. Advised by astronomer Father Christopher Clavius and physician Aloysius Lilius, Pope Gregory XIII ordered that Thursday, 4 October 1582 was to be the last day of the Julian calendar. The next day was Friday, 15 October. For long-term accuracy, every 4th year was made a leap year unless it is a century year like 1700 or 1800. Century years can be leap years only when they are divisible by 400 (e.g. 1600). This rule eliminates three leap years in four centuries, making the calendar sufficiently correct for all ordinary purposes.
Protestant rulers ignored the new calendar that the Pope ordered. It was not until 1698 that Germany and the Netherlands changed to the Gregorian calendar. As mentioned, Britain made the change only in 1752. Russia adopted the new calendar in 1918, China in 1949.
In spite of the leap year, the Gregorian year is about 26 seconds longer than the earth's orbital period. Thus the beginning of the third millennium should have been celebrated at 9:01pm on 31 December 1999. But considering that the Gregorian calendar starts with Year 1, and not Year 0, adding 2000 years means that the third millennium started at 21h00:34s on 31 December 2000. However, because Dionysis Exeguus - the 6th Century monk whose task it was to pivot the calendar around the birth of Jesus Christ - miscalculated the founding of Rome by about 4 years (and left out the year 0), the TRUE THIRD MILLENNIUM actually started on 31 December 1995.
If you are working in UNIX, try this out. At $ prompt, type: cal 9 1752 Surprised??? ?
Isn't the output queer? A month with whole of eleven days missing. This was the time England shifted from Roman Julian Calendar to the Gregorian calendar, and the king of England ordered those 11 days to be wiped off the face of the month of September of 1752. (What couldn't a King do in those days?!) And yes, the workers worked for 11 days less, but got paid for the entire 30 days. And that's how "Paid Leave" was born.