What'S Gregorian Calendar. The gregorian calendar is the most used calendar system in the world today. The gregorian calendar is a solar dating system used by most of the world.

Explore the major differences between the julian calendar and the gregorian calendar, including the exact reasons that necessitated the change to gregorian calendar. Pope gregory xiii issued a papal bull, inter gravissimus on february 24, 1582 that established the gregorian calendar as the new and official calendar of the catholic world.