— United States Naval Observatory  There were two reasons to establish the Gregorian calendar. First, the Julian calendar assumed incorrectly that the average solar year is exactly 365.25 days long, an overestimate of a little under one day per century, and thus has a leap year every four years without exception.
Oct 18, 2023 · 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. The Gregorian calendar differs from the Julian only in that no century year is a leap year unless it is exactly divisible by 400 (e.g., 2000).
- The Editors of Encyclopaedia Britannica
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The 1860s (pronounced "eighteen-sixties") was a decade of the Gregorian calendar that began on January 1, 1860, and ended on December 31, 1869. The decade was noted for featuring numerous major societal shifts in the Americas .
- The original goal of the Gregorian calendar was to change the date of Easter. In 1582, when Pope Gregory XIII introduced his Gregorian calendar, Europe adhered to the Julian calendar, first implemented by Julius Caesar in 46 B.C.
- Leap years don’t really occur every four years in the Gregorian calendar. The Julian calendar included an extra day in February every four years. But Aloysus Lilius, the Italian scientist who developed the system Pope Gregory would unveil in 1582, realized that the addition of so many days made the calendar slightly too long.
- The Gregorian calendar differs from the solar year by 26 seconds per year. Despite Lilius’ ingenious method for syncing the calendar with the seasons, his system is still off by 26 seconds.
- Some Protestants viewed the Gregorian calendar as a Catholic plot. Though Pope Gregory’s papal bull reforming the calendar had no power beyond the Catholic Church, Catholic countries—including Spain, Portugal and Italy—swiftly adopted the new system for their civil affairs.
The adoption of the Gregorian Calendar was an event in the early modern history of most cultures and societies, marking a change from their traditional (or "old style") dating system to the modern (or "new style") dating system – the Gregorian calendar – that is widely used around the world today.
This is a list of adoption dates of the Gregorian calendar by country. For explanation, see the article about the Gregorian calendar . Except where stated otherwise, the transition was a move by the civil authorities from the Julian to the Gregorian calendar.