Adam Clarke on Genesis 1:6

And God said, Let there be a firmament - Our translators, by following the firmamentum of the Vulgate, which is a translation of the στερεωμα of the Septuagint, have deprived this passage of all sense and meaning. The Hebrew word רקיע rakia, from רקע raka, to spread out as the curtains of a tent or pavilion, simply signifies an expanse or space, and consequently that circumambient space or expansion separating the clouds, which are in the higher regions of it, from the seas, etc., which are below it. This we call the atmosphere, the orb of atoms or inconceivably small particles; but the word appears to have been used by Moses in a more extensive sense, and to include the whole of the planetary vortex, or the space which is occupied by the whole solar system.