The Julian calendar had a year about 11 minutes too long, so by the sixteenth century the spring equinox had moved ten days from its date at the Council of Nicaea, threatening the calculation of Easter. On 24 February 1582, Pope Gregory XIII issued the bull Inter gravissimas, based on the work of the astronomer Aloysius Lilius and the Jesuit Christopher Clavius, which cut three leap days every 400 years by making century years leap years only if divisible by 400. Ten days were dropped: in Catholic countries, 4 October 1582 was followed by 15 October. Protestant countries adopted it later, Britain in 1752, Russia in 1918, Greece in 1923.
Before and after
- 1581Construction of Uffizi Gallery
- from 26 July 1581 to 19 January 1795Dutch Republic
- 26 July 1581Act of Abjuration
- from 18 August 1581 to 4 February 1582Siege of Pskov
- 24 February 1582Pope Gregory XIII reforms the calendar
- 3 April 1582Battle of Tenmokuzan
- 26 July 1582Battle of Ponta Delgada
- 23 October 1582Battle of Chuvash Cape
- 1583Founding of University of Edinburgh
More in Science & technology
The era
This moment belongs to the Early modern world (1500 CE to 1760 CE), voyages, printing and new ideas. You can also browse everything in the 16th century.