Gregorian calendar: The Gregorian calendar is the

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. While Julius Caesar's Julian calendar proved useful, it was inaccurate. Learn all about the change to the Gregorian calendar of 1582, from your About.com Guide to Geography. Description The Gregorian calendar , like the Julian calendar , is a solar calendar with 12 months of 28–31 days each. The year in both calendars consists of 365 days, with a leap day being added to February in the leap year s. The months and length of months in the Gregorian calendar are the same as 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 ...