Gregorian calendar

Definition

The Gregorian calendar is the modern calendar used globally, introduced by Pope Gregory XIII in 1582. It refined the Julian calendar to better align with Earth's revolutions around the Sun and to correct seasonal drift.

5 Must Know Facts For Your Next Test

1. The Gregorian calendar has 365 days in a common year and 366 days in a leap year.
2. It was adopted to correct inaccuracies in the Julian calendar's calculation of a year.
3. Leap years occur every four years, except for years divisible by 100 but not 400.
4. The introduction of the Gregorian calendar shifted the date by 10 days to realign with the spring equinox.
5. Not all countries adopted the Gregorian calendar immediately; for example, Great Britain switched in 1752.

Review Questions

• What year was the Gregorian calendar introduced?
• How does the Gregorian calendar determine leap years?
• Why was there a need to shift dates when adopting the Gregorian calendar?

Related terms

Julian Calendar: An earlier calendar system introduced by Julius Caesar that had inaccuracies corrected by the Gregorian reform.

Leap Year: A year which has an extra day added (February 29) to keep the calendar year synchronized with astronomical or seasonal years.

Equinox: The time or date at which the sun crosses the celestial equator, making day and night approximately equal length everywhere on Earth.