OT scholars and Hebraists disagree on the meaning of raqia in Gen 1. John Walton used to think it denoted a solid dome, but changed his mind. Nicholas Petersen has his own theory. Some versions render it as an "expanse." But what, exactly, does that mean–or refer to?
One reason for the disagreement is that we don't have enough occurrences of the word to nail down the meaning. In addition, the meaning is contextual. How does it function in relation to the other elements (e.g. sky, heavens)?
Here's a suggestion: what if raqia is a synonym for "space." Suppose it denotes the space between rainclouds and terrestrial bodies of water (e.g. lakes, oceans, rivers)? Suppose we translate Genesis this way:
6 And God said, “Let there be space in the midst of the waters, and let it separate the waters from the waters.” 7 And God made the space and separated the waters that were under the space from the waters that were above the expanse. And it was so. 8 And God called the expanse Heaven. And there was evening and there was morning, the second day.
If you think about it, that would make perfect sense to the original audience. After all, "space," air, is what separates rainclouds from terrestrial bodies of water. It's the spacious air in-between seems to keep them apart. And that's what the birds fly in.
That's what ancient Hebrews saw when they went outside. That's what they experience. On the one hand there's water at ground level. Bodies of water on the surface of the earth. On the other hand, there's the water that comes down from the sky. Rain or snow from clouds up above. And in-between is empty space.
I think we miss this if we think of the sky or atmosphere as something up above. Overhead. But that's just a part of the space. The space is up and down and all around. Birds fly through space. They fly up from a tree, shrub, grass, or bare ground. And they fly down from to a tree, shrub, grass, or bare ground. Although the sky is the limit, the space begins at ground level. That's the space we freely move through. That's our natural element, in contrast to bodies of water.
In modern parlance, "space" refers to "outer space," but here, space refers to the airy buffer between lakes, oceans, and rainclouds.
Sure, there's space above the clouds, but the description in Genesis is from the perspective of a ground-based observer.