The Julian and Gregorian CalendarsCatholic and Orthodox Calendars

Why does the Roman Catholic Christmas fall on December 25th, and the Orthodox Christmas on January 7th? 

To understand why the Roman Catholic Christmas is 13 days before the Orthodox Christmas we must go back and look at the history of the two calendars. 

The Julian Calendar was created by Julius Caesar in 46 B.C, or in the year 708 which was from the founding of Rome. This would actually be the year -45 if you would use zero as a beginning, and a negative number for B.C. . It is called the 'Old Calendar', or Ecclesiastical Calendar.

Caesar asked Alexandrian astronomer Sosigenes to reform the calendar. Sosigenes used a solar year of 365.25 days. The calendar was set with twelve months and 365 days called Julian dates. To make up for the 1/4 day, he made an exception every 4 years, Leap Years, when the calendar would have 366 days. Leap Years are years that are exactly divisible by 4. Century years are divisible by 400.

Sosigenes created the calendar to follow the equinoxes. To do this, he calculated that 23 days be added after February 23, two months be added between the end of November and the beginning of December, adding 67 days to the then calendar. March 1 would then become January 1. This would start the year on the Spring Equinox (Winter Solstice). Caesar found resistance with the Roman Senate because they took office on January 1. They felt that should be the start of the calendar year. Caesar gave in to politics.

Augustus Caesar also had adjustments made to the Roman Julian Calendar. February had been 29 days, 30 during a Leap Year. He renamed the eighth month Augustus and added an extra day to it. Augustus Caesar would not be out done by Julius Caesar who gave his month Julius (July) 31 days, so Caesar declared that Augustus (August) would also have 31 days. The extra day came from February, which would now be 28 days long. The average number of days in the calendar would be 365.25, with the additional day being added in the Leap Year to February to correct the calendar.

Another change to the calendar came in 525 when the Roman Abbot Dionysius Exiguus devised a system of numbering the years from the birth of Christ, but he was off about 6 years. He used the terms, A.D. for Anno Domini meaning In The Year of Our Lord, which is now called C.E. for Common Era. The other term was B.C., Before Christ, which is now written as B.C.E for Before Common Era. The problem with the Julian calendar was that it would exceed the length of the solar year in 128 years. The calendar would be off by one day from the equinoxes and solstices.This troubled the Christian Church because it affected the date of Easter, which would be slipping into Summer. The date of Easter had been determined in the year 325 by the First Council of Nicea (which today is Iznik, Turkey). Easter would occur around the vernal equinox.

Pope Paul II decided a new calendar was needed. Jesuit Christopher Clavius (1537-1612) devised a new calendar that would be acceptable to the Church, but it wasn't until Pope Gregory XIII that the new calendar was accepted. It would be called the Gregorian Calendar and is currently used by most of the world.

In the Gregorian Calendar 10 days were omitted, Gregorian dates. When the calendar was installed, October 4, 1582, a Thursday, became October 5, a Friday. Then it was adjusted to become Friday, October 15, 1582. The rule for a Leap Year was also changed. It would be divisible by 4 and had to be divisible by 100, then by 400. The extra day would be added after February 28. The first day of the year would be January 1st.

As the Roman Empire spread, so did the use of the Roman Calendar. Italy, Spain, Portugal and Poland adopted the new calendar on October 5, 1582. France and Luxembourg soon followed. Parts of Germany, Belgium, Switzerland, and the Netherlands adopted it in 1584, and other areas between 1699 and 1701. Hungary adopted it in 1587.

An eleven-day correction, instead of 10 days, was made to the calendar in 1752. This was because the Spring Equinox was still off. It was corrected to come on March 21. Britain began to followed the calendar in 1752....Sweden in 1753, Egypt in 1875, Eastern Europe between 1912 and 1919.

The Bolshevik Revolution in Russia brought about major changes to the Gregorian Calendar. The Orthodox Church did not want to be ruled by the Pope and Catholicism. They resisted any changes the Catholic Church tried to make. This included the interruption of when Easter would fall. To keep Easter more accurate with what the Orthodox Church believed, 13 days were removed from the calendar after January 31, 1918. In 1923 the Eastern Orthodox Churches modified the Gregorian Calendar again to keep it in line with the date of Easter. October 1, 1923 in the Julian Calendar would be October 14, 1923 in the Eastern Orthodox Calendar. But it was only the Orthodox religions that would follow the new modified form of the Gregorian Calendar.

Today Russia still uses this changed Gregorian Calendar. The changes are the reason Roman Catholics celebrate Christmas on December 25 and the Eastern Orthodox religion on January 7. There is a 13-day difference.

Why would it be important to know that there is a difference between the Julian and Gregorian Calendars, and the Catholic and Orthodox calendars? Just knowing that there is a difference is interesting, but it is also important for the records we find prior to October 15, 1582, and from the changes made in 1918 and 1923 by the Orthodox Church to the calendar. I have actually found a US baptism record in a Russian Orthodox Church that had a different date of birth for my Uncle than the civil record found. It was only because the Orthodox Church was using the modified calendar. When checking the dates using the 13-day difference, the dates were the same. You just might want to make note of this when finding records from the Catholic and Orthodox areas of Ukraine.