Rosh Hashanah is what 'TODAY' refers to in Psalm 2, "You are My Son, TODAY I have begotten You." Jesus was the "Firstborn of all creation" (Col. 1:15); He is "The Beginning" (Col. 1:18). He called Himself "The Beginning of the Creation of God" (Rev. 3:14). Jesus said: "for out of God I have emerged" (John 8:42 - Gk.). He was the "Son" (Prov. 30:6) of whom Solomon wrote: "From the beginning, before there was ever an earth. When there were no depths I was brought forth, When there were no fountains abounding with water. Before the mountains were settled, Before the hills, I was brought forth; While as yet He had not made the earth or the fields, Or the primeval dust of the world," (Pro 8:23-26). Thus, the six days of creation begin with the begetting of the Son. At the appointed time, the Son "emptied Himself" of His divinity to become fully Man (Phil. 2:5-8), being born of the virgin on Rosh Hashanah, the aniversary of His begetting from His Father "in the beginning."
The book of Revelation provides us with the biblical date of Jesus' birth using astronomy, which falls on Rosh Hashanah, the anniversary of the first day of creation when the Son was brought forth out of God.
1 Now a great sign appeared in heaven: a woman clothed with the sun, with the moon under her feet, and on her head a garland of twelve stars.
2 Then being with child, she cried out in labor and in pain to give birth.
3 And another sign appeared in heaven: behold, a great, fiery red dragon having seven heads and ten horns, and seven diadems on his heads.
4 His tail drew a third of the stars of heaven and threw them to the earth. And the dragon stood before the woman who was ready to give birth, to devour her Child as soon as it was born.
5 She bore a male Child who was to rule all nations with a rod of iron. And her Child was caught up to God and His throne.
The sun is in Virgo during September to early October. The new moon (which becomes visible just after sunset, and sets only minutes later) marks Rosh Hashanah, the new year. Below is a screenshot from Redshift 7 Astronomy Program showing the positions of the sun and moon in relation to Virgo just after dawn on Rosh Hashanah, just after Jesus' birth.