

Adoption of the Gregorian calendar
The adoption of the Gregorian Calendar has taken place in the history of most cultures and societies around the world, marking a change from one of various traditional (or "old style") dating systems to the contemporary (or "new style") system – the Gregorian Calendar – which is widely used around the world today. Some polities adopted the new calendar in 1582, others not before the early twentieth century, and others at various dates between. A few have yet to do so, but except for these, the Gregorian Calendar is now the universal civil calendar, yet old style calendars remain in use in religious or traditional contexts. During – and for some time after – the transition between systems, it has been common to use the terms "Old Style" and "New Style" in dating to indicate which calendar was used to reckon them. Pope Gregory XIII instituted the Gregorian Calendar in 1582 by the Papal bull Inter gravissimas to correct an error in the Julian Calendar that was causing an erroneous calculation...
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