Genesis 1:8 (BSB)

God called the expanse “sky.” And there was evening, and there was morning—the second day.

From Genesis 1. Also in the ESV.

Commentary on Genesis 1:8

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Genesis 1:6-8: We have here an account of the second day's work, the creation of the firmament, in which observe, 1. 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.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Genesis 1:8: And God called the firmament heaven,.... Including the starry and airy heavens: it has its name from its height in the Arabic language, it being above the earth, and reaching to the third heaven; though others take the word "shamaim" to be a compound of two words, "sham" and "maim", that is, there are waters, namely, in the clouds of heaven: and the evening; and...
• Jamieson-Fausset-Brown (Reformed), Commentary Critical and Explanatory on the Whole Bible on Genesis 1:6-8: SECOND DAY. (Gen 1:6-8) 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...
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on Genesis 1:8: And God called the firmament Heaven. And the evening and the morning were the second day. (g) That is, the region of the air, and all that is above us.