Why is this interesting? • 844 implied HN points • 12 Mar 26
- The Julian calendar added slightly too many leap days, so by the 1500s the spring equinox had drifted about ten days from its appointed date and this disrupted the dating of Easter.
- Reformers fixed the problem by skipping ten calendar days and changing leap-year rules: keep a leap every 4 years, but omit leap days in century years unless the year is divisible by 400.
- Pope Gregory XIII introduced the Gregorian calendar in 1582 (Thursday, Oct 4 was followed by Friday, Oct 15), and its rules make the calendar accurate to roughly one day every 3,000 years.