English of Core Text: “And let it divide” — and by how much? Rav Acha bar Yaakov said: By the thickness of a hair.
On the daf / in context: In the discussion of the firmament’s separating function, the Gemara asks the measure of the division and answers with a minimal thickness.
Type of Learning: Custom (measure of the separation)What Is Learned: The dividing function of the firmament is by a hair’s breadth.