Mishna: And these are the festivals of the idolators: Calenda, and Saturnalia, and Kratesis. . .

Gemara: Rav Hanan bar Rava said: Calenda is eight days after the Solstice; Saturnalia is eight days before the Solstice. . .

Our Rabbis taught (in a baraita):

When the first human being saw the daytime diminishing more and more, he said, "Woe is me! Perhaps because I offended, the world is darkened on my account and is reverting to chaos, and this is the death that was imposed on me from Heaven."

He went and sat for eight days, fasting [and praying.]

When he saw the Tevet Solstice, and saw the daytime growing longer, he said, "This is the way of the world."

He went and made a festival for eight days.

The next year, he made both these (days preceding the solstice) and these (days following the solstice) festival days.

He established them for the sake of Heaven, and they established them for the sake of idolatry.