Episode 04

The Gregorian Reform

Ten days that vanished

1582: Gregory XIII skips ten dates so the equinox returns to 21 March. Protestant states resist. Britain waits until 1752. Science and faith argue in the same margin of 0.0078 days per year.

Beats

• Julian drift: one day every 128 years.
• The 400-year leap-year exception.
• Adoption as a map of Reformation politics.

Terms

Tropical year

365.24219 days — equinox to equinox.

Gregorian skip

Century years leap only if divisible by 400.

Discussion

1. Was the reform a scientific act, a liturgical act, or both?
2. What does it mean for a date to 'not exist' in 1582?