Celebrating Rosh Hashana and the Shofar on the First Day of the Seventh Month
The Tanach mentions that the first (day) of the seventh month (Tishrei) shall be for us a solemn rest and a remembrance of blasts, a sacred occasion/convocation; no work shall be done, it shall be a day of blasting for us. See Leviticus 23:24 and Numbers 29:1.
I would like to know how it was determined or concluded that this day of Teruah is the first, head or start of a annual cycle or year, i.e. is named to be a Rosh HaShanah?
And secondly, what are the blasts a reminder of, what is commemorated at the commemoration when the blasts sound on this specific day?
I know the blasts are often interpreted as the sound of the shofar or silver trumpets; but Teruah is also used to describe people shouting in unison or to describe a joyous sound of happiness and celebration. And in Nehemiah 8:2 and 3 we read about the first of the seventh month as a day on which people were attentive to the scroll of the Torah. Looking at a possible explanation for Yom Teruah being seen as a Rosh HaShanah (new year), I found many references to pagan and Babylonian backgrounds; have we maybe turned Yom Teruah into a day it is not, or does the Tanach provides us proof it is a Rosh HaShanah and should be celebrated is the way we do nowadays?