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1582

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1582

Science 16th Century Europe

Pope Gregory XIII Issues Gregorian Calendar Bull

By the late 16th century, the Julian calendar had drifted approximately 10 days from the solar year, pushing the date of Easter progressively later and disrupting ecclesiastical calculations. Pope Gregory XIII, seeking to restore alignment with astronomical reality, commissioned reforms based on the work of astronomer Aloysius Lilius. On February 24, 1582, he promulgated the papal bull Inter gravissimas, which skipped 10 days in October 1582 and adjusted leap year rules by omitting century years not divisible by 400. Catholic countries adopted the new system immediately, while Protestant and Orthodox regions resisted for centuries. The reform established the calendar framework still dominant globally for civil and scientific purposes.

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1582

Science 16th Century Europe

Gregorian Calendar Takes Effect in Europe

By the late 16th century, the Julian calendar had drifted about 10 days behind the solar year due to inaccuracies in leap year calculations, affecting religious observances like Easter. Pope Gregory XIII issued a papal bull in 1582 ordering reform to realign the calendar with astronomical reality. In adopting Catholic countries including Italy, Spain, Portugal, and Poland, Thursday, October 4, 1582, became the last day under the Julian system. The following day was designated Friday, October 15, skipping the intervening dates. This adjustment corrected the drift and introduced refined leap year rules still used worldwide today.

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1582

Law 16th Century Europe

Gregorian Calendar Replaces Julian in Catholic Europe

By the late 16th century, the Julian calendar had drifted about ten days behind the solar year, disrupting the timing of Easter and agricultural cycles across Europe. Pope Gregory XIII issued a papal bull in February 1582 to correct this by adopting a more accurate leap year rule. On October 15, 1582, Catholic territories including Spain, Portugal, Italy, and the Papal States skipped from October 4 directly to October 15, implementing the new Gregorian calendar. The reform, developed with input from astronomers like Christopher Clavius, restored alignment with the equinoxes. Protestant nations adopted it gradually over subsequent centuries, while some regions delayed until the 20th century.

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