Firmament

The firmament refers to the sky conceived as a solid or structured expanse, like a dome, above the earth. In ancient Near Eastern and biblical literature, it is often described as a clear boundary that separates heaven above from the earth below and serves as the place that the sun, moon, and stars move through. It also was thought to hold back the cosmic, upper waters and is frequently referred to in Hebrew, Jewish, and Christian apocalyptic literature where it is described as a crystal structure on which is the heavenly temple and God's throne.