Gregorian

blog 365

From the Julian to the Gregorian Calendar

The Gregorian Calendar, also known as the “Western Calendar” or “Christian Calendar”, is the most widely used calendar around the world today.

The Gregorian Calendar is named after Pope Gregory XIII.

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The Gregorian Calendar's 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 or solar year.

Too many Leap Years

The reason why the Julian Calendar was out of step with the tropical year was the rule it used to define a Leap Year. The Julian Calendar had only one rule to determine whether a year would have 29 days in February instead of 28. If the year could be divided by 4 then it was considered to be a Leap Year. The Gregorian Calendar on the other hand has a more complicated rule for calculating what years will be Leap Years:

• The year must be evenly divisible by 4;
• If the year can be evenly divided by 100, it is not a Leap Year, unless;
• The year is also evenly divisible by 400. Then it is a Leap Year.

These rules result in fewer leap years, minimizing the inaccuracies of the Julian Calendar.

http://www.timeanddate.com/calendar/julian-gregorian-switch.html