1,335. An Arc of Visibility from 10 to 12 Degrees

Rabbi Jack Abramowitz

Hilchos Kiddush HaChodesh 17:18

If the arc of visibility is between 10 and 11  degrees, or greater than 11, and the first longitude is 12 degrees or higher, the moon will certainly be visible. If the arc or the first longitude is smaller than this, the moon will not be visible.

Hilchos Kiddush HaChodesh 17:19

If the arc of visibility is between 11 and 12 degrees, or greater than 12, and the first longitude is 11 degrees or higher, the moon will certainly be visible. If the arc or the first longitude is smaller than this, the moon will not be visible.