December 25th is the day when the Christians celebrate Nativity of Jesus – however there are no sources that would prove Christ indeed was born on that particular day. The decision about establishing Christmas on December 25th was carefully considered by the Early-Christian Church, and it was accepted as late as in 4th century AD! We may say now that it had quite much to do with the Sun.
In the Julian calendar the winter solstice (which is the shortest day of the year) was on December 25th – that means that beginning from this date there was more and more Sun every day. It is therefore the day of “re-birth of the Sun”, celebrated in many ancient cultures. The solar gods were worshiped in almost all the religions. There were many of such cults in the ancient Roman Empire – we associate it mostly with the cult of Helios, Apollo, or Mitra. In the late-Roman period there was a new syncretic cult introduced officially: so called Sol Invictus, that is Invincible Sun. In 274 AD the emperor Aurelian accepted it as an official Roman cult. In Roman calendar from 354 AD we may find a feast on December 25th, called Natalis Invicti – which is the Nativity of the Invincible Sun.
Naturally, the Christians adopted some customs and elements of religious beliefs that had already existed in their society and adjusted them to their own veneration of Christ. That is why in the Early-Christian art we may find the depictions of Christ portrayed as Apollo-Helios, or the Invincible Sun. It usually comes not only with depicting Christ in radiant glory and in the chariot, but also includes portraying him as a young man clean shaved. Such a depiction of Christ with no beard nor mustache was not that uncommon after all – we usually call it the Apollo-type Christ.
The Sun is also related to Christ on the other day, which is March 25th – it is around the vernal equinox and for the ancient Romans it used to be the beginning of a new year. For the Christians, on the other hand, it is a beginning of the Salvation – that day is the moment of Christ’s conception during the Annunciation. Of course as a result the Birth of Christ occurs 9 months later, which is December 25th. The solar symbolics has been associated with Christ for the centuries – as an example we may look at the print by Albrecht Dürer, depicting Christ as Sol Iustitiae (the Sun of Justice). As the personification of Justice Christ holds its attributes: the scale and the sword, and he is sitting on a lion, which refers to the Biblical throne of Solomon, the wisest judge. On the other hand, a lion is actually an animal associated with the solar symbolism as well – it is yellow and its head decorated with the mane resembles the Sun surrounded by the rays. Interestingly, we can also observe here the motif of the burning eyes (as it is not glasses neither a masque what he is wearing) – that actually refers to the description of the Son of Man that we may find in the Revelation: “his eyes like a burning flame” (Rev: 1.14).
And finally it is worth mentioning that the emperor Constantine the Great (the one worshiped as a Christian Saint!) declaired Sunday, “the Day of Sun”, as the Roman day of rest. The name of this day in the Germanic languages still preserves the ancient solar-cult tradition (English Sunday, German Sonntag, Scandinavian Søndag, Söndag). In the Romance languages it rather refers to the “Day of Lord” (Latin dies Domino dicata, Italian Domenica, French Dimanche, Spanish Domingo). In most of the Slavic languages, on the other hand, it is associated with “ne dělatĭ”, meaning “not working” (Polish Niedziela, Czech Neděle, Croatian Nedjelja). It seems that the Mediterranean cultures focus on the Christian traditions, while the Germanic Northern Europe preserves more of the pagan roots. Anyway, it is understandable that in Northern Europe people focus on worshiping the Sun, as they tend to miss it for quite a big part of the year. And what about the Central Europe? Well, apparently Slavic people living here just like to have rest and they define this day as the day of laziness. It seems the good way to celebrate any feasts of holidays – so I wish you well-spent, lazy Christmas, just in a Central-European way!