Gregorian Calendar

Because the Julian year, averaging 365.25 days, was somewhat longer than the actual length of a solar year, which is known to be 365.242199 days, the discrepancy between the Julian calendar and the seasons had increased to 10 days by the late sixteenth century. 

• Fixed holy days started to fall in the “wrong” season, both for the church and for farmers, who relied on specific holy days to schedule planting and harvesting. 

• From the year 1582, Pope Gregory XIII issued a reform that removed 10 days; in that year, October 15 was the day following October 5. 

• This adjustment, along with the removal of leap days in “century” years unless they were evenly divisible by 400 (e.g., 1600, 2000), rectified the calendar to the point that only rare “leap seconds” are required to keep months and seasons in sync today. 

The Gregorian calendar (N.S., or New Style), which was originally used exclusively in Roman Catholic nations, gradually gained acceptance across the West and is now used by the majority of the globe, at least for business and government.

You may also want to learn more about Global Calendar Systems here.

Julian Calendar

In 46 B.C., Julius Caesar ordered the conversion of the reformed Roman lunar calendar to a solar calendar. The ninety-day intercalation fixed a developing mismatch between the seasons and the months in which they had historically fallen. 

• The Roman municipal year had become approximately three months “ahead” of the seasons prior to this intercalation, thus spring started in June. 

• To make the correction, the year 46 B.C. was given 445 days and was dubbed ultimus annus confusionis, or "the final year of the confused counting." 

• The new calendar, which was based on the Egyptian solar calendar, had a 365-day year with an extra day in February every fourth year. 

• The Julian year has an average length of 365.25 days after adding this leap year and day, which is quite near to the real solar cycle. 

The Julian calendar (O.S., or Old Style) has been in use in the West for over 1,600 years, and it is still the foundation for the “Old Calendarist” Orthodox Christian liturgical calendar, which is utilized by all Orthodox Christian churches to establish Easter dates.

You may also want to learn more about Global Calendar Systems here.