Δαφνη Ευτυχια Αρθουρος

"So God throws open the door of this world--and enters as a baby. As the most vulnerable imaginable. Because He wants unimaginable intimacy with you. What religion ever had a god that wanted such intimacy with us that He came with such vulnerability to us? What God ever came so tender we could touch Him? So fragile that we could break Him? So vulnerable that His bare, beating heart could be hurt? Only the One who loves you to death." -- Ann Voskamp

[To most of my fellow Christians, on this first day of Christmas, I wish you a joyous celebration of the Nativity of Our Lord, and may you keep the Christmas spirit through the rest of Christmastide as well! Advent is finished and Christmas is begun! To non-Christians celebrating our holiday today, I wish you a merry Christmas, whatever it means to you, as well -- and to everyone not celebrating in one way or another, may you have a pleasant and peaceful Monday with the rest of us out of your hair for a spell. Finally, for those of my faith who are not celebrating the Nativity today -- those in old-calendar Coptic, Georgian, and Russian churches -- may the remainder of your Advent be good, and your Christmas two weeks hence be wonderful!]

Yay, Christmas is begun! Christmas lasts either forty days^[1], or twelve days followed by twenty eight days of Epiphanytide. The days in the song, "The Twelve Days of Christmas"? These are those. (This list doesn't include every single feast day during Christmastide. And no, I didn't know all of these off the top of my head; I had to look up a bunch of this. Note also that I'm trying to merge info about multiple denominations.)

Christmas / Christmastide^[1] / Twelvetide:

[1] From Wikipedia: "In medieval era Christendom, Christmastide 'lasted from the Nativity to the Purification.' To this day, the 'Christian cultures in Western Europe and Latin America extend the season to forty days, ending on the Feast of the Presentation of Jesus in the Temple and the Purification of Mary on 2 February, a feast also known as Candlemas because of the blessing of candles on this day, inspired by the Song of Simeon, which proclaims Jesus as 'a light for revelation to the nations'.' Many Churches refer to the period after the traditional Twelve Days of Christmas and up to Candlemas, as Epiphanytide, also called the Epiphany season." This is why some folks take down their Christmas decorations 6 Jan and others take them down 2 Feb. If you take them down before Epiphany, I shall pout at you and complain that Christmas isn't over yet.

[2] Dates given are for whichever calendar a church uses for liturgical purposes. For most, this is the Gregorian calendar. For Coptic churches, and old-calendar Orthodox Churches (Georgian, Russian), these would be Julian-calendar dates. So old-calendar Orthodox churches still celebrate Christmas Eve on "24 December", but it's Julian 24 December, which is currently equivalent to Gregorian 5 January.

[3] From Wikipedia: Catholic -- "the first Sunday after 6 January or, if in a particular country the Epiphany is celebrated on 7 or 8 January, on the following Monday." Church of England -- "Epiphany may be observed on 6 January proper, or on the Sunday between 2 and 8 January. If Epiphany is observed on a Sunday on 6 January or before, the Baptism of Christ is observed on the following Sunday. If the Epiphany is observed on 7 or 8 January, the Baptism of Christ is observed on the following Monday." Episcopal Church [USA] -- "Epiphany is always celebrated on January 6, and the Baptism of the Lord is always celebrated on the following Sunday. It is not clear as to whether or not the Feast of the Baptism of our Lord is the end of Christmastide for the Episcopal Church."

[4] Okay, you can argue that the first verse and the refrain have to be while they're on their way, so during Advent and the twelve days, but the last verse has to be on Epiphany and the middle verses are ambiguous, yes? Anyhow, as I see it the subject is Epiphany.

[5] Wikipedia again: "In the Church of England, the Mother Church of the Anglican Communion, the Presentation of Christ in the Temple is a Principal Feast celebrated either on 2 February or on the Sunday between 28 January and 3 February."