Gregoriánus

Gregoriánus refers to things associated with Pope Gregory XIII, primarily the calendar reform he instituted. The Gregorian calendar, introduced in 1582, is the most widely used civil calendar in the world today. It replaced the Julian calendar, which had been in use since Roman times but had a slight inaccuracy in its leap year calculation. This inaccuracy caused the calendar to drift out of sync with the seasons over centuries.

The Gregorian calendar corrects this drift by introducing a more precise rule for leap years. A year is a leap year if it is divisible by four, except for years divisible by 100 but not by 400. This adjustment ensures that the calendar remains aligned with the Earth's orbit around the sun with much greater accuracy. The transition from the Julian to the Gregorian calendar involved skipping days to realign the calendar with astronomical events, such as the vernal equinox. While initially adopted by Catholic countries, its accuracy and practicality led to its gradual adoption by Protestant and Eastern Orthodox countries over the following centuries. The term "Gregoriánus" can also be used to refer to Gregorian chant, a form of plainchant sung in the Roman Catholic Church, which is named after Pope Gregory I, also known as Saint Gregory the Great. However, in common usage, "Gregoriánus" most often signifies the calendar.