You are correct. The Vernal equinox is the Turn of the Year when the days become longer than the nights....and continue to the Summer Solstice. The scriptures tell us that the lights in the heavens are for signs and seasons....for days and years [Genesis 1:14]. The Hebrew word for sign is owth (Strong's #226) and it means; a flag, a beacon, a monument....evidence. Something that is obviously seen.
The word for Seasons mow'ed (Strong's #4150) and it means; an appointment, a fixed time especially... a Festival.
It is therefore very understandable that the Sun (Equinox) and the Moon phases (Months) are the determining factors in Yahweh's calendar. One other condition given....is the condition of the barley which is planted in the fall.
[Exodus 12:2] This month shall be unto you the beginning of months: it shall be the first month of the year to you.
When Yahweh gave this information to the Israelites He told them that this would be the first month in the year. He didn't tell them it was the beginning of the year because the Equinox and the New Moon do not coincide very often (only about 5 times a year). Coincidentally...the new moon conjunction of Nisan and the Equinox in 30 A.D. happened on the same day, March 23 (Nisan 1). It was a Thursday. The actual beginning month of the year is the first new moon after the Vernal Equinox. Since in 30 A.D. they occurred jointly.... that was the beginning of that year and the beginning of the first month of that year.
Some folks say it's the new moon closest to the Vernal Equinox....but stop and think. If a new moon occurred 6 days before the Equinox it would be occurring in the previous year....and this often will happen under the Jewish Calendar put together by Hillel II in the 4th century A.D. Yahweh says to look at the lights in the heavens and not calculate it like the Jews have done.
There is indeed a beginning (and an ending) to Yahweh's holy calendar:
[Deuteronomy 11:12] A land which the LORD thy God careth for: the eyes of the LORD thy God are always upon it, from the beginning of the year even unto the end of the year.
He has chosen to begin His year in the spring when life begins to manifest itself after the dead of winter. It is the observance of the Vernal Equinox that tells us when winter has now become spring and the days are now longer than the nights.....and the first new moon after this event tells us when the first month begins.
The Vernal Equinox, however.... does not determine the mow'eds....the appointed times. It is the new moon which does this. The sun (the Equinox) determines the year. The Moon (the month) determines the days. The scripture tell us that the law shall go forth from Jerusalem [Isaiah 2:3][Micah 4:2] so the years, the months and the days are determined from visible sighting of the lights in the heavens from Israel (Jerusalem) and this is also what guides the planting and the harvesting times.
Now the green ears of barley is the third thing we are told to watch for in determining the season and the wave sheaf offering from the first harvest of the year. Barley ripens much earlier than wheat [Exodus 9:31] although they are both planted in the fall.
[Exodus 23:15]Thou shalt keep the feast of unleavened bread: (thou shalt eat unleavened bread seven days, as I commanded thee, in the time appointed of the month Abib; for in it thou camest out from Egypt: and none shall appear before me empty) (Abib is the same month as is Nisan)
[Leviticus 2:14]And if thou offer a meat offering of thy firstfruits unto the LORD, thou shalt offer for the meat offering of thy firstfruits green ears of corn dried by the fire, even corn beaten out of full ears.
Passover occurs on the 14th day of Nisan [Leviticus 23:5] and the Feast....the next day [Leviticus 23:6]. The green barley is beaten out of the full ears indicating a fully ripened grain that is then winnowed. You read quite a bit about that in the Book of Ruth [1:22; 2:2-3; 2:17; 2:23; 3:2; 3:15-17]. The reason corn is mentioned as the grain in the above paragraphs is the fact the Israelites did not observe Passover in the desert after the "Golden Calf" incident [Exodus 32] and the additional "National" disobedience in not entering the Promised Land on schedule [Numbers 14]. They were then condemned to spend forty years before they could again celebrate the Passover.
When Joshua took them over Jordan they again celebrated the Passover after the wave offering.....but it was Canaanite corn as they, of course did not have their own crops to harvest [Joshua 5:10-12].
So....these three things determine the Yearly Feasts. They begin after the Equinox in the spring (easily determined by a simple sundial) and then the first new moon after that with the Passover (the 14th day) determining the schedule for the rest of the year....but only if the barley is ripe and the green ears are winnowed.
In the fifth paragraph that should read.....five times a century....not five times a year (when the Equinox and the New moon occur simultaneously).
Yes on Genesis 1:14. But the moon phases are not relevant to the counting from the ‘Vernal equinox’ 14 days. Now I think it is curious that conception took place at the winter solstice, birth took place near the time of the autumn equinox, crucifixion took place near the spring equinox... but what event took place near the summer solstice? This is not a trick question because I do not know.