January 6 - Epiphany Day
In the Orthodox calendar the feast of the Epiphany is called 'Theophania', meaning the manifestation of God. Epiphany is the most ancient feast, after Easter, relating to the Lord and is observed by the Christian Church on January 6. The first evidence attesting to the feast of the Epiphany comes from Clement of Alexandria who died about 215 AD. He relates that a Gnostic group observed the Baptism of our Lord on January 6 believing that it was at the time of Baptism that Divinity took the flesh in Christ. The date of January 6 was selected because according to some ancient reckoning the day began to grow longer on that date and so it was celebrated by pagans as the day of victory of light over darkness. In Rome, though, the day of the birth of the Invincible Sun was celebrated on December 25. In both East and West and practically at the same time, these two pagan festivals were replaced by a Christian feast signifying the epiphany (manifestation) 'of the sun of justice' and 'of the true light of the world'.
http://en.wikipedia.org/wiki/Epiphany_Day