A society is a hard thing to hold together. If you live in an agrarian society, as the overwhelming majority of people did until about two hundred years ago, and you are on the western edge of Europe, few times are harder than the dead of Winter. The days are at their shortest, the sun is far away, and the Malthusian edge is right in front of you. It’s no wonder so many religious festivals take place around the solstice.
He celebrated it at newgrange
Newgrange is a clock. The shaft leading out to the roof box is precisely aligned so that on the morning of the Winter Solstice the first light of day will run directly into the middle of the tomb. Or, at least, it was precisely so aligned. It is so old that changes in the Earth’s orbit have affected its operation.