Adam HaRishon was created in the Jewish month of Tishrei (end of September / beginning of October). Meaning, the winter was right around the corner. The Talmud Tractate Avodah Zarah (Idol-worship) 8a teaches that when Adam experienced his first winter and saw the duration of each daytime gradually decreasing, he got very scared. He thought that, because of his sins, G-d had decided to darken the world and return it to the former state of Tohu and Bohu.
Adam started panicking and began to pray and repent. However, when he, later on, saw that that duration of each daytime gradually increased, he went and in thanksgiving established Eight Festival Days.
Adam established these festive days for the sake of heaven but later generations turned these festivals into idolatry.
The question is raised why Adam was able to make such a mistake. Didn’t he perfectly know how the world functions? One explanation is that he was depressed and so caught up in his guilt feelings that he simply stopped thinking rationally.
In the future, the Romans would turn the winter and summer solstice into idol-worship festivals. The same with the Teutons.
A Jew is not allowed to participate in the holidays of idol-worship nations and thus he cannot participate in today’s solstice events, as they are still connected to idolatry.