[baryphonic]

Christmas celebrations far predate the conversion of Scandinavia. The early Christians in the Roman Empire were celebrating Christmas on December 25 since the second century or so. It was officially marked on the church calendar in the fourth century after Christianity became the state religion of Rome.

There isn't much evidence that the solstice involves major celebrations predating Christmas. Whatever small celebrations did happen may have been appropriated by Christians, which makes sense given the persecution they faced.

I'm all likelihood, the date December 25 (winter solstice) was chosen as being nine months after the celebration of the Annunciation on March 25 (spring equinox) where the Virgin Mary was told she would give birth to Christ.

Throughout the history of Christianity, Christians have incorporated local traditions into our rituals and festivals, but placed into their proper framing and order (i.e. the one God is the source of all creation and is goodness). When Christianity came to Northern Europe, the church incorporated Yule festivities, placed into the proper order with Christ at the center and not the old Norse pantheon.

The arguments about Christians actually celebrating pagan holidays are from certain (usually) Calvinist reformers who had a revisionist interpretation of various Christian traditions, and felt they had debased Christ's church. The Puritans in England, for example, banned Christmas after they took power in the English Civil War, which suppressed the holiday (at first legally, then culturally) until Charles Dickens essentially revived it in the 19th century. Today, atheists have simply appropriated the Calvinist arguments for themselves.