- Theories regarding the origin of the date of Christmas

Many different dates have been suggested for the celebration of Christmas. No explanation of why it is celebrated on December 25 is universally accepted. Theories include the following:

The Catholic Encyclopedia article on "Christmas" offers a starting point for Christmas, which does not appear among the earliest lists of Christian feasts, those of Irenaeus and Tertullian.

The earliest evidence of celebration is from Alexandria, about AD 200, when Clement of Alexandria says that certain Egyptian theologians "over curiously" assign not just the year but the actual day of Christ's birth[4], on 25 Pachon (May 20) in the twenty-eighth year of Augustus.

By the time of the Council of Nicaea, AD 325, the Alexandrian church had fixed a dies Nativitatis et Epiphaniae.

The December feast reached Egypt in the 5th century.

In Jerusalem, Egeria the 4th-century pilgrim from Bordeaux, witnessed the feast of the Presentation, forty days after January 6, which must have been the date of the Nativity there.

At Antioch, probably in 386, St John Chrysostom urged the community to unite in celebrating Christ's birth on December 25, a part of the community having already kept it on that day for at least ten years.

It is an appropriation of the pagan Midwinter festivals, such as the Germanic Yule and the Roman festival of the birth of Unconquered Sun, celebrated on the day after the winter solstice, or the Roman festival of Saturnalia.

It derives from the tradition that Jesus was born during the Jewish Festival of Lights (Hanukkah, the 25th of Kislev and the beginning of Tevet).

Kislev is generally accepted as corresponding with December. Under the Old Julian calendar, the popular choice of 5 BC for the year of Jesus' birth would place the 25th of Kislev on the 25th of November.

The date of Christmas is based on the date of Good Friday, the day Jesus died. Since the exact date of Jesus' death is not stated in the Gospels, early Christians sought to calculate it, and arrived at either March 25 or April 6.

To then calculate the date of Jesus' birth, they followed the ancient idea that Old Testament prophets died at an "integral age"—either an anniversary of their birth or of their conception.

They reasoned that Jesus died on an anniversary of the Incarnation (his conception), so the date of his birth would have been nine months after the date of Good Friday—either December 25 or January 6.

Thus, rather than the date of Christmas being appropriated from pagans by Christians, the opposite is held to have occurred. [See Duchesne (1902) and Talley (1986).]

The apparition of the angel Gabriel to Zechariah, announcing that he was to be the father of John the Baptist, was believed to have occurred on Yom Kippur.

This was due to a belief (not included in the Gospel account) that Zechariah was a high priest and that his vision occurred during the high priest's annual entry into the Holy of Holies.

If John's conception occurred on Yom Kippur in late September, then his birth would have been in late June. (The traditional date is June 24.) If John's birth was on June 24, then the Annunciation to the Blessed Virgin Mary, said by the Gospel account to have occurred three month's before John's birth, would have been in late March. (Tradition fixed it on March 25.)

The birth of Jesus would then have been on December 25, nine months after his conception. As with the previous theory, proponents of this theory hold that Christmas was a date of significance to Christians before it was a date of significance to pagans.

It was appropriated from the birthday of Mithras, a savior figure of a Greco-Roman mystery religion who was popular with the Roman Legions.