George Washington was born on both February 11, 1731 and over a year later on February 22, 1732. The reason for the discrepancy was the dramatic change from Julian calendar to Gregorian calendar later in his life.It wasn't really over a year's worth of correction, though, because Britain (and her colonies, including America) used March 25th as the first day of the new year. In the Julian system Washington was born in the month before the new year, in the Gregorian he was born a month after the new year.
They made the switch in 1752. Here's how it went down:
- 1582 - Pope Gregory XIII declared the Julian calendar would be replaced by the Gregorian. The reason for the change? The Julian calendar had 365.25 days per year (1 leap year every four years). The number of earth rotations in a single earth revolution around the sun is 365.24250, and it took over a thousand years to realize that the seasons were subtly shifting.
- All the Catholic countries switched immediately.
- 1751 - England decided this year would last from March 25th to December 31st -- 282 days.
- The first day of 1752 was January 1st.
- Easter and Lent and all the other holidays based on the vernal equinox were celebrated as usual.
- September 2nd was followed by September 14th. Eleven days were removed* to readjust the equinoxes to the correct time**.
Thus, if you count backwards using the Gregorian calendar to the day that Washington was born you arrive at February 22, 1732, a difference of 11 days and one year from what his birth certificate said.
It turns out that Washington favored the switch and happily adopted the 22nd as his new birthday while many of his contemporaries held on to the old style for theirs. Maybe it made him feel younger.
* To prevent this from happening again we skip three leap days every four hundred years.
** The "correct time" was based on the Council of Nicaea's decision in 325 AD to commemorate the vernal equinox*** each year on March 21st.
*** An equinox occurs when night and day are approximately of equal duration. This happens twice a year when the earth's axis of rotation is perpendicular to the sun's rays.