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Gregorian calendar
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Stone relief on Pope Gregory XIII's tomb in Saint Peter's Basilica, showing the pope seated among clergy as a figure presents a document and another gestures to a globe.
What Is Leap Day?
Interactive Gregorian calendar tool with fields for year, month, day, and era, set to December 8, 2025, and a blue Calculate button at the bottom.
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Stone relief on Pope Gregory XIII's tomb in Saint Peter's Basilica, showing the pope seated among clergy as a figure presents a document and another gestures to a globe.
Gregorian calendar The introduction of the Gregorian calendar, depicted in relief on the tomb of Pope Gregory XIII in St. Peter's Basilica, Vatican City.

Gregorian calendar

dating system
Also known as: New Style calendar
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History

Gregorian calendar, solar dating system now in general use. It was proclaimed in 1582 by Pope Gregory XIII as a reform of the Julian calendar. By the Julian reckoning, the solar year lasts 365 1/4 days, and the intercalation of a “leap day” every four years was intended to maintain correspondence between the calendar and the seasons. However, the solar year more precisely lasts 365 days, 5 hours, 48 minutes, and 45.25 seconds—that is, more...

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