Gregorian calendar: Learn about the origins

Learn about the origins, evolution and accuracy of the Gregorian calendar , the most widely used calendar in the world. Find out how it differs from the Julian calendar , how it aligns with the seasons and astronomical events, and how it names the months of the year. The Gregorian calendar is the 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 Gregorian calendar is the calendar used in most parts of the world. [1][a] It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The Gregorian calendar is used throughout most of the modern world. Invented in 1582, the system adopted a leap year cycle different than the one employed by the Julian calendar . The new calendar was considered an improvement on the earlier Julian model. In the Gregorian calendar , four years make up a cycle, with an extra or “leap” day added to the fourth year to keep the dates and months synchronized with the solar cycle. Although the Gregorian calendar was named for Pope Gregory XIII ...