I believe sundown on our Sunday, Sept. 13th is actually the start of Tishri 1.
The days go from sundown to sundown. Elul 29 starts at sundown on Saturday, Sept. 12 and ends at sundown Sunday Sept. 13.
It could be, depending on when the actual new moon is physically sighted. It is strongly expected to be 1 day later, when the moon will be 5% illuminated.
It is guesswork, as Yeshua told his disciples: “of that day knoweth no man but the Father which is in Heaven.”
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