Why do we celebrate the feast of the Nativity on the 7th of January, while some other churches celebrate it on the 25th of December. What is the reason for this difference?
It is not a doctrinal or a theological difference, but it is a scientific difference.
It is known that the year is 365 days and a quarter of a day. Therefore a day is added once every four years; and the year is called a leap year. But in the Gregorian western calendar, it has been said that the year is 365 days and a quarter of a day and approximately 11 minutes. This calendar was established about fifteen centuries AD.
If this difference of eleven minutes every year, is multiplied during those centuries since the birth of Christ until now, it will result into a difference of approximately thirteen days which is the difference between the 25th of December and the 7th of January.
We have confidence in our Coptic calendar, because of the great excellence of the Pharaohs in the science of astronomy, and we celebrate the Nativity on the 29 th of Kiahk which corresponds to the 7 th of January. There are some other churches who share with us this date.
But the question in not a question of faith and doctrine, nevertheless it can be exploited to impress the simple, when the date is changed.