When did Rosh HaShana become Rosh HaShana?

2 Questions-

1. How is it that the Jewish new year starts in the 7th month of the year

2. How did Rosh HaShana go from yom teruah to day of Judgement?

   As the name implies Rosh HaShana(RH) is the "head of the year".  This implies that it is the beginning of the year.  Yet all the holidays in the Torah are measured by ordinal numbered months starting with Nisan 

in the spring.  So when did RH become the beginning of the year?  This is a separate question from- When did RH become conceptually the holiday that it is today-ie a holiday establishing the kingship of G-d and the beginning of the period known as the 10 days of repentance.  

     

    In regards to the second question:  The Torah mentions the holidays 5 times.  They are Shemos perek 23 and 34, Vayikra 23, Bamidbar 28-29 and Devarim 16.  Rosh HaSh,kana is mentioned only in Vayikra and Bamidbar.  It is called yom teruah in Bamidbar 29:1 and called zichron teruah in Vayikra 23:24. Rashi says that the zichron  is to remember or to recite the verses relating to shofar and zichronot that remind us of the akeidah(the binding of Isaac).  I think that on a simpler level the teruah was for the purpose of inaugurating  the month which contained Sukkot( and Yom Kippur).  Sukkot was for the mass population the holiday par excellence .  In fact when the word Chag is used in Tanach it almost always refers to Sukkot.  The Chag or Hag is cognate with the Semitic/Arabic word Haj which really means pilgrimage rather than holiday.  And in fact it was such a festive pilgrimage during temple times.  Rosh HaShana as a holiday was a much lower profile holiday.  Its importance was more related to the temple.

   The only explicit reference to RH in later Tanach is Yechezkel 40:1, and its hard to know if Yechezkel is actually referring to RH as we know it.  The 9th chapter of Nechemiah tells of events on the the first of the 7th month, but it bears litttle resemblance to our holiday.  By the time of the writing of the book of Jubilees,in the 2nd century BCE the holiday gets barely a mention in that book where the Avot(patriarchs)celebrated all the Jewish holidays prior to the giving of the Torah.Interestingly the book of Jubilees gives the origin for "days of remembranceas relating to the story of the Flood.  By the time of the Mishneh, (2nd Century of the common era) .though , the concept of a day of judgement is already in place. So an evolutionary path in the concept of RH can be traced.

   With regards to the first question- when is the beginning of the year?  Certainly every date in the Torah should be assumed to go according to the ordinal number scheme starting in the spring.  However in Shemot  Chag Ha'asif (agricultural harvest festival) is related to tzeit hashana (the going out of the year)  or in chapter 34 tekufat hashana.( the turning of the year).  Both these phrases imply the year end would be in the fall.  And so it was in the middle east of the second millenium. There were places and times when the year would start in the spring and places where it would start in the fall.  The Gezer calendar is a famous archaeological piece that outlines the agricultural tasks of the year.   Ot date to the 10th century BCE, and it starts in the fall.  

  The conclusion, I think is that a dual calendar system was in place.  The ritual year and the counting method of the Torah started with Nisan as the first month.  The agricultural year started and ended in the fall with the harvest followed by the joyous Sukkot festival.