Julian calendar

Retrato de Julio César (26724093101) (cropped)

Julian to Gregorian Date Change

Bogojavlenie

Julian calendar

The Julian calendar, introduced by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect on 1 January 45 BC (AUC 709), by edict. It was the predominant calendar in the Roman Empire, and most of Europe, for more than 1,600 years, until replaced by the more accurate Gregorian calendar in 1582.

History

The Julian calendar was designed to approximate the solar year. The previous Roman calendar was a lunar system that required regular adjustments to keep it in line with the solar year. Caesar, advised by the Alexandrian astronomer Sosigenes, sought to simplify things and align the calendar with the solar year. The Julian calendar introduced a leap year system, which added an extra day to February every four years.

Structure

The Julian year is, on average, 365.25 days long, divided into 12 months. The lengths of the months in the Julian calendar are the same as those in the Gregorian calendar, which succeeded it. The major difference between the two calendars is the formula used to calculate leap years. In the Julian system, any year evenly divisible by four is a leap year. This results in an average year length of 365.25 days, which is slightly longer than the solar year.

Months

1. January - 31 days 2. February - 28 days, 29 in leap years 3. March - 31 days 4. April - 30 days 5. May - 31 days 6. June - 30 days 7. July - 31 days 8. August - 31 days 9. September - 30 days 10. October - 31 days 11. November - 30 days 12. December - 31 days

Leap Year Rule

The rule in the Julian calendar to determine a leap year is straightforward: any year divisible by four is a leap year. This rule, however, leads to an excess of leap years, making the calendar drift with respect to the equinoxes.

Reform and Replacement

The Julian calendar's slight discrepancy from the solar year (about 11 minutes per year) led to a drift of approximately one day every 128 years. By the 16th century, this drift had caused the spring equinox to fall on March 11 instead of March 21. To correct this, Pope Gregory XIII introduced the Gregorian calendar in 1582, which has a more refined leap year system.

Legacy

Despite its replacement, the Julian calendar is still used by some Eastern Orthodox churches for liturgical purposes. It also continues to be of interest for historical studies and is used in some astronomical calculations.

See Also

• Gregorian calendar
• Leap year
• Roman calendar
• Timekeeping