Firmament, meaning a vast expanse of a firm structure. How could they have known the atmosphere is like a solid structure which literally burns up iron meteors and satellites which hit it? And shields us from most harmful solar radiation? A VERY accurate description!
There are three heavens listed in the Bible. The atmospheric heaven, the heaven of space, and the heaven where God dwells. "and God set them in the firmament of heaven to give light upon the earth." Gen 1:17. (he set them in space).
No, the Bible isn't a science textbook, but it is light years ahead of other ancient writings, and is accurate when it does touch on science.
