Calvin thought that the firmament need not be interpreted literally, allegorically, or philosophically. He merely thought that God taught in relation to what people thought they saw. According to Calvin, Moses said that there was a firmament, because people’s natural sense told them there was a barrier above them holding back the water.
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. Here the Spirit of God would teach all men without exception; and therefore what Gregory declares falsely and in vain respecting statues and pictures is truly applicable to the history of the creation, namely, that it is the book of the unlearned. The things, therefore, which he relates, serve as the garniture of that theater which he places before our eyes. Whence I conclude, that the waters here meant are such as the rude and unlearned may perceive.~ Calvin’s Commentary on Genesis
However Calvin was a geocentrist. Why? Because he was rude and unlearned to the Heliocentric Theory. Psalm 93:1-2 says the following.
93:1 The Lord reigns!
He is robed in majesty,
the Lord is robed,
he wears strength around his waist.
Indeed, the world is established, it cannot be moved.
93:2 Your throne has been secure from ancient times;
you have always been king.
This is how Calvin looked at these verses.
A simple survey of the world should of itself suffice to attest a Divine Providence. The heavens revolve daily, and, immense as is their fabric, and inconceivable the rapidity of their revolutions, we experience no concussion — no disturbance in the harmony of their motion. The sun, though varying its course every diurnal revolution, returns annually to the same point. The planets, in all their wanderings, maintain their respective positions. How could the earth hang suspended in the air were it not upheld by God’s hand? By what means could it maintain itself unmoved, while the heavens above are in constant rapid motion, did not its Divine Maker fix and establish it?
In Calvin’s mind the Bible taught that there was a solid firmament above us to communicate to the ignorant. Clearly Calvin believes that the Bible also teaches the sun revolves around the earth. Like the firmament is there any need to appeal to allegory or metaphor? Perhaps the Bible says that the sun revolves around the earth, because until Galileo every reader believed that it did. Perhaps the world “cannot be moved” “such as the rude and unlearned may perceive.”