What is the relation between the month Nisan and the spring equinox?

Question

I'm searching for the relation between Nisan and the spring equinox according to Scripture.

I know of the texts Genesis 1:14, Exodus 12:2-3, Leviticus 23:15 and Deuteronomy 16:1.

I find multiple definitions, I quote:

1. First lunar crescent after the spring equinox (= 1 Nisan)
2. New moon nearest to the spring equinox is the start of the year (= 1 Nisan)
3. Pesach (15 Nisan) must occur in the spring (i.e, after the equinox), in most cases 1 Nisan occure before the equinox
4. The Rabbis give the rule that the 16th of Nisan (at sunset beginning it) should occur after the beginning of the year.

I think 4) is the right one but can someone give me the rigth interpretation with texts in Scripture why a definition is right or wrong?

Answer 1

In the Babylonian calendar, which Jews used in the late pre exilic, exilic, and early post exilic periods, the 1st of Nisannu always fell after what we would consider to be the equinox (though not necessarily after the equinox as the Babylonians counted it.) By the Herodian period, it is not certain that Judea is following Babylon any more. Josephus says that 14 Nisan occurs "when the sun is in Aries" (Antiquities 3.10.5), that is, on or after the equinox. In the Talmud, the equinox is given as one of three conditions, two of which must obtain for an intercalation.

Our Rabbis taught: A year may be intercalated on three grounds: on account of the premature state of the corn-crops; or that of the fruit trees; or on account of the lateness of the equinox. Any two of these reasons can justify intercalation, but not one alone. (Tractate Sanhedrin)

The Tosefta gives a rule for intercalating on account of the equinox:

The year is not to be intercalated unless the spring equinox is still distant the greater part of a month. How much is the greater part of a month? Sixteen days. R. Jehuda says: Two thirds of a month, twenty days. T. Sanhedrin 2.7.

The Rabbinic calendar, which dates from the period C.E. 700-950, though a late Jewish tradition gives it a date in the 4th century C.E., seems to have been designed always to put the 15th or 16th of Nisan after the equinox. And due to a slight solar drift in the Rabbinic calendar, the 16th of Nisan is now always after the equinox. The 15th of Nisan can not now fall before March 26th in the Gregorian calendar, and in the 8th, 11th, and 19th years of the 19 year cycle, the 16th of Nisan can be a month after the equinox. as it was in 2016.

Answer 2

If nobody in this famous community answers I give the answer from scripture as good as I can. The calendar is defined through Moses by watching the sun and the moon.

1. The first day of every month is the day you watch with a naked eye the first visable crescent of the moon. This is one or two days after the New Moon (0% visability).
2. The first month is found by watching the sun. The spring festival must be in the first month. This means that the 15th of the first month must be on or after the first day of the spring. The first day of the spring is when you see sunset exactly in the west.

God says that we have to guard the first month to have 3 festivals in a year (Deuteronomy 16:1,16). To guard this an extra month is inserted if necessary in the old year to prevent the spring festival starts in winter and we have 2 or 4 festivals in a year in stead of the required 3. In the end this seems to me clear and not complicated what I first thought. I think it is strange that there are so many different voices.

You can see the moon and the sun in the past with the open source program Stellarium. You have to set the atmosphere on to take into account atmospheric correction for the human eye.

I'd appreciate it if someone respond.