The Julian calendar, the predecessor to the modern Gregorian calendar, didn’t quite fully account for leap year shenanigans, and so drifted be about 1 day every century. The Gregorian calendar changed the way leap year works, but didn’t reset the beginning of the year. It just froze the drift where it was at the time.
The Julian calendar, the predecessor to the modern Gregorian calendar, didn’t quite fully account for leap year shenanigans, and so drifted be about 1 day every century. The Gregorian calendar changed the way leap year works, but didn’t reset the beginning of the year. It just froze the drift where it was at the time.
https://en.m.wikipedia.org/wiki/Gregorian_calendar