The historical dates of Yule.

2 sources:

Hakon the Good was a Norwegian king, who tried to force Christianity on Norway (hence he is called “the Good.”) In the Saga of Hakon the Good, Hakon moved Yule from its traditional time on the Heathen Lunar calendar, to be at the same time as christian celebration called christmas.

Chapter 15 of the saga "Hakon the Good":
“King Hakon was a good Christian when he came to Norway; but as the whole country was heathen, with much heathen blot, and as many great people, as well as the favor of the common people, were to be conciliated, he resolved to practice his Christianity in private. But he kept Sundays, and the Friday fasts, and some token of the greatest holy-days. He made a law that the festival of Yule should begin at the same time as Christian people held it, and that every man, under penalty, should brew a meal of malt into ale, and therewith keep the Yule holy as long as it lasted. Before him, the first night of Yule was on hǫkunótt, that is midwinter night, and Yule was held for three nights."

The Chronicon of Thietmar of Merseburg Chapter 17 (circa 925 AD):
"As I have heard odd stories concerning their ancient mid-winter sacrifices (blots), I will not allow this custom to be ignored. The middle of that kingdom is called Lederun (Lejre), in the region of Sjælland, all the people gathered every nine years in January, that is after we have celebrated the birth of the Lord, and there they offered to their gods sacrifices…”