The Gregorian Calendar, also known as the Western or Christian Calendar, is the most widely used calendar in the world today. Its predecessor, the Julian Calendar, was replaced because it did not properly reflect the actual time it takes the Earth to circle once around the Sun, known as a tropical year.
Too Many Leap Years
The reason the Julian Calendar had to be replaced was the formula it used to calculate leap years. The Julian formula produced a leap year every four years, which is too many. The Gregorian Calendar uses a much more accurate rule for calculating leap years.
