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Science24 February 1582

Introduction of the Gregorian Calendar

Also called: Gregorian calendar, Inter gravissimas

In 1582 Pope Gregory XIII promulgated a new calendar correcting the error of the Julian calendar — the calendar the world uses today.

Commission for the reform of the calendar presided over by Gregory XIII — Sienese Biccherna book cover, 16th century
Commission for the reform of the calendar presided over by Gregory XIII — Sienese Biccherna book cover, 16th century

Unknown author · Public domain · Source

The Julian calendar set by Julius Caesar counted the year as 365.25 days, about eleven minutes too long, so that by the 16th century the spring equinox had drifted ten days early and the date of Easter was off. Adopting a scholars’ proposal, Gregory XIII issued a bull on 24 February 1582 ordering that 4 October that year be followed by 15 October, and that years divisible by 100 be leap years only if also divisible by 400.

Catholic countries soon followed, but Protestant and Orthodox lands were slower: Britain changed in 1752 and Russia only in 1918, after the Revolution. Joseon adopted this solar calendar in 1896 in the Eulmi Reform.

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States at the time
Papal States
Places
Rome

People

  • Gregory XIII1502 – 1585

    creator · Pope from 1572 to 1585 who in 1582 promulgated the new calendar that corrected the Julian calendar — the Gregorian calendar

Before and after

Earlier
1571 Battle of Lepanto
Later
1610 Galileo’s Telescope and His Trial

Themes that include this event

  • Scientific Revolution, Enlightenment and the English Revolutions1543 – 1796

    The Scientific Revolution from Copernicus to Newton, parliamentary government in England won through the Puritan and Glorious Revolutions, and the Enlightenment that sought to remake society by reason — the groundwork of the civic revolutions and the Industrial Revolution