The Firmament

In the Bible, the firmament is a solid, dome-shaped structure in which the stars were placed. It separated the waters below from the waters above. Windows in the firmament were opened whenever it rained.

Verses in the KJV that refer to the firmament:
Gen.1:6-8, 1:14-15, 1:17, 1:20
Ps.19:1, 150:1
Ezek.1:22-26, 10:1
Dan.12:3

The Flat Earth Bible Robert J. Schadewald
Heaven and Earth: The World the Biblical
Writers Thought They Lived In
Dr. Bob Price and Reginald Finley, Sr.
Wikipedia: Firmament