The Hebrew word raqia translated firmament: “The Hebrew meaning of something ‘made firm’ by beating or stamping, e.g. a hammered piece of metalwork. It usually refers to the curve of the heavens, which to an observer on the ground appears like a vast inverted bowl of blue. In passages like Genesis 1:6; Psalms 19:1; 150:1; Daniel 12:3, it clearly has this meaning, but in Ezekiel it has the sense of a firm, level surface or platform. In the book of Revelation this same phrase becomes ‘a sea of glass, like crystal’ before the throne of God (Revelation 4:6).”

"Spread out above the heads of the living creatures was what looked something like a vault, sparkling like crystal, and awesome. Under the vault their wings were stretched out one toward the other, and each had two wings covering its body. When the creatures moved, I heard the sound of their wings, like the roar of rushing waters, like the voice of the Almighty,[b] like the tumult of an army. When they stood still, they lowered their wings. Then there came a voice from above the vault over their heads as they stood with lowered wings. Above the vault over their heads was what looked like a throne of lapis lazuli, and high above on the throne was a figure like that of a man. I saw that from what appeared to be his waist up he looked like glowing metal, as if full of fire, and that from there down he looked like fire; and brilliant light surrounded him. Like the appearance of a rainbow in the clouds on a rainy day, so was the radiance around him. This was the appearance of the likeness of the glory of the Lord. When I saw it, I fell facedown, and I heard the voice of one speaking. Ezekiel 1:22-28