George washington was born in Virginia on the 11th February 1731 and celebrated his birthday on that date for 19 years. Virginia was a British colony and used the Julian calendar.

Then things got complicated.

The Julian calendar had a 12-month year measuring 365.25 days - an attempt to duplicate the time it takes the Earth to make a complete revolution around the sun. However, the calendar exceeded the solar timetable by about 11 minutes a year. Over time, that error compounded so that every 128 years the calendar shifted out of sync by a full day.

As a result, by the late 16th century there was a 10-day discrepancy between the astronomical definition of time and the calendar's definition. Easter, for example, was sliding toward summer.

To rectify this, in 1582, Pope Gregory XIII decreed a calendar reform, starting with a new way of determining leap years, that cut the annual time discrepancy from 11 minutes down to about 30 seconds. And, to bring the secular calendar back in line with the sky calendar, 10 days were dropped from the month of October that year.

In essence, 'You went to bed on October 4 and woke up October 15,' said Geoff Chester, public affairs officer for the U.S. Naval Observatory in Washington.

The change to the new Gregorian calendar wasn't universally accepted, however. Great Britain and its colonies, for example, continued on the Julian system until 1752, by which time they were 11 days out of whack with most of the world.

In another oddity, the British celebrated New Year's on March 25.

The switch to the Gregorian calendar meant dramatic changes for the British Empire: The year 1751 was cut off at Dec. 31, rather than extending to March 24, according to reference books.

The day after Dec. 31, 1751, was Jan. 1, 1752 - meaning, in essence, that the days Jan. 1 to March 24, 1751, were dropped from the outgoing British Calendar, and became Jan. 1 - March 24, 1752, under the newly adopted Gregorian system.

So while George Washington turned 19 on Feb. 11, 1750 (under the Julian calendar), his 20th birthday was celebrated in February 1752 (under the Gregorian).

In the changeover to Gregorian, Britain eliminated 11 days from the month of September (similar to what was done in 1582) and Parliament ordered that dates prior to 1752 on the Julian calendar be moved 11 days.

That pushed Washington's birthday back to Feb. 22. The switch acknowledged that even though he was born Feb. 11, 1731, according to the Julian calendar, to most of the world (which was using the Gregorian calendar) it was Feb. 22, 1732.