So verse 6 says, and God said, let there be a firmament in the midst(middle) of the waters(what is in the middle of all waters?) And let it divide the waters from the waters.
7 and God made the firmament, and divided the waters which were under the firmament from the waters which were above: and it was so.(Heaven has water above and bellow, it is in the middle)
8 And God called the firmament Heaven...
I study the bible. If you don't believe in it just entertain the idea. Any input?