Day of Atonement

Be careful to celebrate the Day of Atonement on the tenth day of that same month — nine days after the Festival of Trumpets. You must observe it as an official day for holy assembly, a day to deny yourselves and present special gifts to the Lord.
Leviticus 23:27-28

Trying to explain holidays to folks who don't observe them is not always an easy undertaking. This evening I looked up the definition of the Hebrew New Year on Wiki. As one explanation, Wiki writes:

Rosh Hashanah marks the beginning of the civil year, according to the teachings of Judaism, and is the traditional anniversary of the creation of Adam and Eve, the first man and woman according to the Hebrew Bible, as well as the initiation of humanity's role in G*d's world.

News to me! Imagine telling someone that a holiday commemorates the creation of the first man and woman. I don't recall reading that the Almighty had made a calendar anywhere in Genesis. So where did that come from?

I don't recall any formal atonement in my life. Celebration and atonement are private events to me. <SHRUG>.