There are many points of view regarding Yahweh's calendar. The point of this study is not to analyze or present all the points of view regarding calendar. The following represents what I believe to Yahweh's calendar according to the scriptures. For the record, I believe that Yahweh's month begins when we can see the first part of the crescent after the moon has been in the dark phase.
According to the word of Yahweh, the lights in heaven were meant to be for signs, seasons, days and years:
Genesis 1:14 - Then Elohim said, "Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs and seasons, and for days and years; 15 "and let them be for lights in the firmament of the heavens to give light on the earth"; and it was so. 16 Then Elohim made two great lights: the greater light to rule the day, and the lesser light to rule the night. [He] [made] the stars also. 17 Elohim set them in the firmament of the heavens to give light on the earth, 18 and to rule over the day and over the night, and to divide the light from the darkness. And Elohim saw that [it] [was] good.
Yahweh set the greater light to rule the day. Yahweh set the lesser light to rule the night. Obviously this is the sun and the moon respectively. Yahweh set them to be signs for "seasons". This word 'seasons' comes from the Hebrew word "Moed" (Strong's #4150). Which is translated "feast" 23 times in the King James version. It literally means "Appointed time". In the scriptures, it is obvious that the 'lesser light' is to be used to determine the feasts of Yahweh. All throughout scripture, Yahweh uses the word that is translated 'month' which literally means "new moon" in Hebrew to determine the times of His feasts. (What we will be discussing later).
If you were to look on a calendar today, you would see one of the days marked as the "new moon". Scientists today regard the new moon as "conjunction", which the moment the moon is in between the sun and the earth. But if we were to go by the conjunction, we may find ourselves in some interesting scenarios. Suppose the conjunction was at 7:39pm and evening (the beginning of Yahweh's new day) was also at 7:39pm. On which day would the new moon be? Did the ancients possess the technology to determine these things? Certainly no. But even if they did, evening would begin a little later if you were only 40 miles further west. You would find yourself in a situation where it was the new month in one town, but the next town west the new month began a day later. This is confusion.
The word used for "New Moon" in Scripture is Strong's #2320. It is translated "month" and "New moon" in the King James version. The root word from this is #2318, "chadash" which means "to be new". Imagine yourself as a shepherd boy out in the fields, tending your flocks. Night by night you observed the moon waning until it no longer emitted light. From your perspective it was gone. Then on an evening when the moon started to emit light again, it was a "new moon". Thus it was the new month. This is so simple that anyone can understand it. From my perspective, anything beyond this is a complicated and forced interpretation.
When the new year begins
If we were to only use twelve moons per year as our guide to the scriptural year, soon the seasons will fall behind because there can be either 12 or 13 moon phases during the time the earth travels around the sun. Obviously, Yahweh was quite aware of this fact. Yahweh's calendar is agriculturally based. With the planting of seed and harvesting of crop, this was a representation of His people. There are many references to this in the parables of Yahushua. The first month of Yahweh's calendar began with the month of Abib in the spring:
Exodus 12:2-3 - "This month [shall] [be] your beginning of months; it [shall] [be] the first month of the year to you. Speak to all the congregation of Israel, saying: `On the tenth [day] of this month every man shall take for himself a lamb, according to the house of [his] father, a lamb for a household.
The above verse is the beginning of Yahweh's commandment concerning Passover. This month is called the month of Abib:
Deuteronomy 16:1 - "Observe the month of Abib, and keep the Passover to Yahweh your Elohim, for in the month of Abib Yahweh your Elohim brought you out of Egypt by night.
According to the Theological Wordbook of the Old Testament, "Abib" carries the following meaning:
"This noun refers to barley that is already ripe, but still soft, the grains of which are eaten either rubbed or roasted"
This makes sense because the ripened barley will be waved before Yahweh as a "wave sheaf offering" during the Feast of Unleavened Bread.
Leviticus 23:10-11 Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of the firstfruits of your harvest unto the priest: 11 And he shall wave the sheaf before Yahweh, to be accepted for you: on the morrow after the sabbath the priest shall wave it.
So Yahweh calls the first month of the year, "Abib" and He requires a sheaf of ripened barley to be waved before him during that first month. The word that is translated "Observe" in Deuteronomy 16:1 is Strong's #8104, 'Shamar'. It's meaning can have the essence of watching and waiting for something. In fact, this word is translated "Watch" in the following verse:
Psalm 130:6 - My soul waiteth for Yahweh more than they that watch (8104) for the morning: I say, more than they that watch (8104) for the morning.
And so, Yahweh is literally saying:
"Observe/watch the New Moon of Ripened Barley and keep the Passover to Yahweh your Elohim".
Therefore, the first month of Yahweh's year is the month in which one may find barley that will be ready for the wave sheaf offering . This is how I believe that Yahweh's people kept up with the seasons according to His word. They didn't need astronomical calculations to keep the word of Yahweh, but Yahweh gave His sign to His people that His new year had begun when they would see the new moon with fresh, young barley ears in their crops. This would mean that during the 12th moon, there would be some years when the barley was not ready because it was too early in the spring. These years would contain 13 months in them. How simple! No need for complicated astronomical calculations.
So then, the barley harvest represented the beginning of Yahweh's new year and it was in fact, what was used in the Wave Sheaf offering during the Feast of Unleavened Bread in the first month of the year. These are some of the reasons I believe Yahweh's calendar is partly based on watching. Watching for the new moon and watching for harvestable barley.