And when the moon rises one-fourteenth part appears in the heaven: the light becomes full in her on the fourteenth day she accomplishes her light.1st Enoch 77:6
Moon rising = 1/14th part (first visible sliver)
and when she is illumined throughout, her light is accomplished full in the heaven1st Enoch 77:11
Light accomplished = 14 days into the cycle = illumined throughout = Full Moon
And on the first day she is called the new moon, for on that day the light rises upon her1st Enoch 77:12
1st Enoch 77:6 And when the moon rises one-fourteenth part appears in the heaven
Light rising upon her = 1/14th part = first sliver = new moon according to Enoch
On the side whence the light of the moon comes forth, there again she wanes till all the light vanishes and all the days of the month are at an end, and her circumference is empty, void of light1st Enoch 77:14
Light vanishes = empty moon = last day of the month.
This is how we arrived at spotting the first visible sliver is the new moon. Blessings and shalom.