One of the first things you will probably notice when studying any chart of the Biblical Calendar is that they do not fall on specified dates according to the Gregorian calendar that we use today. The reason is that the Gregorian calendar (adopted in 1582 during the reign of Pope Gregory XIII) is a solar one that is related to the earth’s revolution around the sun. The Biblical Calendar, in contrast, is based on a lunar (moon) calendar.
A year on the Gregorian calendar runs 365 days. But since it takes approximately 365 and a 1/4 days for the earth to make a complete circle around the sun, an extra day is added in February every four years, making a Leap Year of 366 days. The Biblical calendar is based upon the movement of the moon around the earth. A full circle takes about 29 days. Thus, twelve of these lunar months add up to 354 days in a year. So, a solar year is 11 days longer than a lunar year. By the way, the 12 months correlate to the 12 tribes, which correlate to Jacob’s 12 sons. (That’s another study!)
In Deuteronomy (Devarim) 16:16, G-d instructed the people to come to Jerusalem (Yerushalayim) three times a year to observe the feasts. As they came, they observed ceremonies given by G-d that were performed in both the temple (Beit HaMikdash) and the home.
YOM KIPPUR/ DAY OF ATONEMENT – Lev 16:1-34; 23:26-32; Num 29:7-11; Ro 3:24-26; Heb 9:7; 10:3, 30-31; 10:19-22; Act 27:9;