I saw this re-posted on a friend's blog. I thought I would share it here. However, I'm just gonna post the most important part. If you wanna read the whole thing you can go to the website.http://www.orthodox-christianity.com/?p=542 (Calculating Christmas)
or this one:http://www.touchstonemag.com/archives/article.php?id=16-10-012-v (Calculating Christmas)
So in the East we have April 6th, in the West, March 25th. At this point, we have to introduce a belief that seems to have been widespread in Judaism at the time of Christ, but which, as it is nowhere taught in the Bible, has completely fallen from the awareness of Christians. The idea is that of the “integral age” of the great Jewish prophets: the idea that the prophets of Israel died on the same dates as their birth or conception.
This notion is a key factor in understanding how some early Christians came to believe that December 25th is the date of Christ’s birth. The early Christians applied this idea to Jesus, so that March 25th and April 6th were not only the supposed dates of Christ’s death, but of his conception or birth as well. There is some fleeting evidence that at least some first- and second-century Christians thought of March 25th or April 6th as the date of Christ’s birth, but rather quickly the assignment of March 25th as the date of Christ’s conception prevailed.
It is to this day, commemorated almost universally among Christians as the Feast of the Annunciation, when the Archangel Gabriel brought the good tidings of a savior to the Virgin Mary, upon whose acquiescence the Eternal Word of God (“Light of Light, True God of True God, begotten of the Father before all ages”) forthwith became incarnate in her womb. What is the length of pregnancy? Nine months. Add nine months to March 25th and you get December 25th; add it to April 6th and you get January 6th. December 25th is Christmas, and January 6th is Epiphany.
Christmas (December 25th) is a feast of Western Christian origin. In Constantinople it appears to have been introduced in 379 or 380. From a sermon of St. John Chrysostom, at the time a renowned ascetic and preacher in his native Antioch, it appears that the feast was first celebrated there on 25 December 386. From these centers it spread throughout the Christian East, being adopted in Alexandria around 432 and in Jerusalem a century or more later. The Armenians, alone among ancient Christian churches, have never adopted it, and to this day celebrate Christ’s birth, manifestation to the magi, and baptism on January 6th.
Western churches, in turn, gradually adopted the January 6th Epiphany feast from the East, Rome doing so sometime between 366 and 394. But in the West, the feast was generally presented as the commemoration of the visit of the magi to the infant Christ, and as such, it was an important feast, but not one of the most important ones—a striking contrast to its position in the East, where it remains the second most important festival of the church year, second only to Pascha (Easter).
In the East, Epiphany far outstrips Christmas. The reason is that the feast celebrates Christ’s baptism in the Jordan and the occasion on which the Voice of the Father and the Descent of the Spirit both manifested for the first time to mortal men the divinity of the Incarnate Christ and the Trinity of the Persons in the One Godhead.
A Christian Feast
Thus, December 25th as the date of the Christ’s birth appears to owe nothing whatsoever to pagan influences upon the practice of the Church during or after Constantine’s time. It is wholly unlikely to have been the actual date of Christ’s birth, but it arose entirely from the efforts of early Latin Christians to determine the historical date of Christ’s death.
And the pagan feast which the Emperor Aurelian instituted on that date in the year 274 was not only an effort to use the winter solstice to make a political statement, but also almost certainly an attempt to give a pagan significance to a date already of importance to Roman Christians. The Christians, in turn, could at a later date re-appropriate the pagan “Birth of the Unconquered Sun” to refer, on the occasion of the birth of Christ, to the rising of the “Sun of Salvation” or the “Sun of Justice.”