The Firmament of Genesis 1:7

 

The image above was located by an advanced Google image search, which search specified that the results could be used, even modified, without violating copyright. It shows the firmament as a dome over the earth, with stars and moon fixed in the firmament. 

The Wikipedia article on "firmament" says this:

In biblical cosmology, the firmament is the structure above the atmosphere of Earth, conceived as a vast solid dome.^[1] According to the Genesis creation narrative, God created the firmament to separate the "waters above" the earth from the "waters below" the earth.^[2] The word is anglicized from the Latin firmamentum, which appears in the Vulgate, a late-4th-century Latin translation of the Bible.

Some public domain comments on "firmament," which word was used in the King James Version of the Bible:
Genesis 1:6 And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
8 And God called the firmament Heaven. And the evening and the morning were the second day.

Other versions use "expanse," and "vault," and probably other words.

Matthew Henry's commentary says this:
The command of God concerning it: Let there be a firmament, an expansion, so the Hebrew word signifies, like a sheet spread, or a curtain drawn out. This includes all that is visible above the earth, between it and the third heavens: the air, its higher, middle, and lower, regions-the celestial globe, and all the spheres and orbs of light above: it reaches as high as the place where the stars are fixed, for that is called here the firmament of heaven (v. 14, 15), and as low as the place where the birds fly, for that also is called the firmament of heaven, v. 20. When God had made the light, he appointed the air to be the receptacle and vehicle of its beams, and to be as a medium of communication between the invisible and the visible world; for, though between heaven and earth there is an inconceivable distance, yet there is not an impassable gulf, as there is between heaven and hell. This firmament is not a wall of partition, but a way of intercourse. See Job 26:7; 37:18; Ps. 104:3; Amos 9:6.

John Calvin's commentary says this: The work of the second day is to provide an empty space around the circumference of the earth, that heaven and earth may not be mixed together. For since the proverb, 'to mingle heaven and earth,' denotes the extreme of disorder, this distinction ought to be regarded as of great importance. Moreover, the word "rakia" comprehends not only the whole region of the air, but whatever is open above us: as the word heaven is sometimes understood by the Latins. Thus the arrangement, as well of the heavens as of the lower atmosphere, is called "rakia" without discrimination between them, but sometimes the word signifies both together sometimes one part only, as will appear more plainly in our progress. I know not why the Greeks have chosen to render the word [indecipherable], which the Latins have imitated in the term, "firmamentum"; for literally it means expanse. And to this David alludes when he says that 'the heavens are stretched out by God like a curtain,' (Psalm 104:2.) If any one should inquire whether this vacuity did not previously exist, I answer, however true it may be that all parts of the earth were not overflowed by the waters; yet now, for the first time, a separation was ordained, whereas a confused admixture had previously existed. Moses describes the special use of this expanse, to divide the waters from the waters from which word arises a great difficulty. For it appears opposed to common sense, and quite incredible, that there should be waters above the heaven. Hence some resort to allegory, and philosophize concerning angels; but quite beside the purpose. For, to my mind, this is a certain principle, that nothing is here treated of but the visible form of the world. He who would learn astronomy, and other recondite arts, let him go elsewhere.

Robert Jamieson says:
6. firmament--an expanse--a beating out as a plate of metal: a name given to the atmosphere from its appearing to an observer to be the vault of heaven, supporting the weight of the watery clouds. By the creation of an atmosphere, the lighter parts of the waters which overspread the earth's surface were drawn up and suspended in the visible heavens, while the larger and heavier mass remained below. The air was thus "in the midst of the waters," that is, separated them; and this being the apparent use of it, is the only one mentioned, although the atmosphere serves other uses, as a medium of life and light.  

Interesting. The Bible was written in accord with the way contemporary people viewed the universe, and, at least in Henry's case, commented on from a related viewpoint.

Added June 17, 2022: This post shows that Answers in Genesis, the most prominent Young-Earth Creation organization, does not believe that there is, or was, a firmament.

Thanks for reading.