Hello Brother Bill,
"While leading the Hebrew host from bondage to freedom, the Lord was firmly establishing them in the truth of all things, including the truth of the day on which the year begins, of the day on which the month begins, and of the day on which the week begins. Obviously, the Hebrew religion had largely to do with the days of the week, of the month, and of the year.
The Hebrews were forever to keep holy, (1) not a seventh, but the seventh, day of each week, the Sabbath; (2) the days from the fifteenth to the twenty-first day of the first month, the Passover week; (3) the fiftieth day after the sheaf of the first fruits was offered, the Pentecost; (4) the tenth day of the seventh month, the Atonement; (5) the days from the fifteenth to the twenty-first day of the same month, the Feast of Tabernacles; and (6) the feasts of the new moons. Thus the All-knowing One, He who created the heavenly bodies and knows the very moment He set them in motion to govern the day, the month, and the year, decreed that the holy feasts be observed in the very month and on the very day on which they were first ordained.
And He appointed the "lights in the firmament... for signs, and for seasons, and for days, and years" (Gen. 1:14), by the movements of which He fixed each solar and each lunar date, so that it could never be lost sight of. Then to make doubly secure against such a loss. He "spake unto Moses and Aaron in the land of Egypt, saying, This month shall be unto you the beginning of months: it shall be the first month of the year to you." Ex. 12:1, 2.
Thus we see that His great and never erring timepiece for earth, the earth's own invariable movements, fix the day and the year; whereas the moon's revolving round the earth makes the months.
But the Roman New Year, January 1, finds its establishment, not in the movements of the solar system, but in the notions of mythology. Consequently, as the date does not coincide with either the vernal or the autumnal equinox, or with either the summer or the winter solstice, then should earth's inhabitants ever lose count of the day, and need to recover it, they would be helpless to do so.
To prevent His people from bringing upon themselves such a catastrophe, and to have them intelligent as to the time the year begins, the Lord gave to Moses the sacred yearly calendar, which cannot be lost or miscalculated so long as the earth remains. He told him that the day which preceded the exodus was the fourteenth day of the first month; and that forever thereafter, they were to commemorate the Passover on that very night each year, the night following the fourteenth day. Thus was the Lord re-stablishing the creation calendar, reaffirming that the year begins on the day of the vernal equinox, on which spring, the first season of the year, commences, and on which the sun and the moon were created (the fourth day from the beginning of creation)--the only point in time at which, in the very nature of things, the year could begin. And so it is that the Passover, the Atonement, and the Feast of Tabernacles (the three most important feasts in the year), besides other feasts, are controlled by the solar year and by the lunar month; the weekly Sabbath by the day on which creation began; and the year itself by the vernal equinox, the immovable sign-post.
Beginning its first month of the year with the first new moon, at, or after, the vernal equinox, March 20-21, it puts the fourteenth day, that on which the Passover lamb was to be slain, on April 3. Once for all, is seen the utter impossibility of the Roman month's having the slightest thing to do with fixing the time of either the Passover or the sheaf offering, and thus not the slightest thing to do with reckoning the time of either the crucifixion or the resurrection of Christ.
This is more graphically seen from the correspondence of the sacred events which came in the spring of the year A.D. 31, the year Christ was crucified, with the sacred events which came in the fall of the year A.D. 27, the year in which He was baptized, as viewed diagrammatically
This chart enables us to see that just as one solar season matches another (the vernal equinox matches the autumnal equinox, and the summer solstice, the winter solstice), in like fashion the sacred feasts of one season match the sacred feasts of another season: the tenth day of the first month, the separation of the unblemished lamb from the flock (Ex. 12:3), corresponding to the tenth day of the seventh month, the work of Atonement, the separation of the righteous from the unrighteous, signifying in both events a day of judgment, a day of separating the holy from the unholy; the sixteenth of the first month, the day Christ was crucified, corresponding to the sixteenth of the seventh month, the day He was baptized, showing that His watery grave foreshadowed His grave in the tomb; the eighteenth day of the first month, the resurrection, corresponding to the eighteenth day of the seventh month, the first day of the wilderness temptation; His forty days of victorious ministry to His disciples, corresponding to His forty days of victorious conflict with Satan; and His disciples' preaching the gospel after the Pentecost, corresponding to His preaching the gospel after the wilderness temptation."
We find that in 1844 the vernal equinox was on March 21 and the first new moon "at or after" that date was on April 19. This placed passover of that year on May 2 and the atonement of that ear on Oct. 22. If you want to find the day of atonement or any other day of any other year all you need to do is this:
Find out when the vernal equinox is of that year.
Then you need to find out when the first new moon is of that year:
-Keep in mind that the new moons as recorded by astronomers is when the moon is fully unseen. However, the biblical new moon is when you can actually observe the first sliver, this is why its called "new" not "gone". So for example, this year, the astronomers place the first new moon on April 3. Biblically, it is actually the night of April 4, because that is when you will start to see it. Also, according to Gen 1:5 the evening is the beginning of the day, so the night of April 4 is actually already into what we would call April 5.
Putting it all together, we see that this year, for example, the day of atonement will be on October 8 because that is ten days from the day of the new moon of the seventh month.
Hopefully this was somewhat helpful.
May the Lord Bless you and lead you into All Truth.