Why did George Washington’s birth date change?
Until the 16th Century, the Julian calendar was used. But, astronomers observed a discrepancy between the Julian calendar and the true solar year. In 1582, Pope Gregory XIII implemented a revised calendar, the Gregorian or New Style, calendar, which required the elimination of ten days to correct the accumulated celestial system error. The Gregorian calendar included leap years to maintain accuracy.
However, not all countries adopted the new calendar immediately, and by the time Britain and its colonies adopted it in 1752, eleven days needed to be eliminated to account for errors in the Julian calendar.
When the conversion took place, although George Washington had been born on February 11, 1731, by the Julian calendar, the date became February 22, 1732.