The Gregorian Calendar
The Gregorian calendar is today's internationally accepted civil calendar and is also known as the Western or Christian calendar.
12 Irregular Months
Replaced Julian Calendar
The Gregorian calendar's predecessor, the Julian Calendar, was replaced because it was too inaccurate. It did not properly reflect the actual time it takes the Earth to circle once around the Sun, known as a tropical year.
Realigned With the Sun
The Julian calendar's formula to calculate leap years produced a leap year every four years. This is too often, and eventually the Julian calendar was several days out of sync with the fixed dates for astronomical events like equinoxes and solstices.
New Leap Year Formula
- New formula for calculating leap years:
- The year is 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
- 10 days were dropped in October 1582
- New rules for calculating Easter-dates
Is Any Calendar Perfect?
The more advanced leap year formula makes the Gregorian calendar far more accurate than the Julian. However, it is not perfect either. Compared to the tropical year, it is off by one day every 3236 years.
Who Designed the Calendar?
Although the Gregorian calendar is named after Pope Gregory XIII, it is an adaptation of a calendar designed by Italian doctor, astronomer and philosopher Luigi Lilio (also known as Aloysius Lilius). He was born around 1510 and died in 1576, six years before his calendar was officially introduced.
|The Gregorian Calendar|
|Used in||Most of the world|
|Accuracy||1 day in 3236 years|
|Number of days||Common year: 365|
Leap year: 366
|Number of months||12|
|Correction mechanism||Leap day|
- Gregorian Calendar
- Julian Calendar
- Revised Julian Calendar
- Islamic Calendar
- Jewish Calendar
- Persian Calendar
- Mayan Calendar
- Chinese Calendar
- Roman Calendar
- Ethiopian Calendar
- Switch from Julian to Gregorian
- Is There a Perfect Calendar?
- What Do CE and BCE Mean?