1:6-8 DAY TWO expanse/firmament/Heaven, under waters (surface of earth), upper waters.
In verses 14 & 17 it references the sun, moon, and stars are created "in the expanse of the heavens (now plural). So it would be my understanding that the expanse created on day 2, taking nothing away or adding nothing to scripture, would reach from the surface of the earth to wherever the upper waters may be, so it would include our sky/atmosphere and space.
It is interesting that "Heaven" is capitalized in verse 8, but not in 14 & 17.
Psalm 148:4 Praise him, you highest heavens, and you waters above the heavens!
Proverbs 25:3 As the heavens for height, and the earth for depth, so the heart of kings is unsearchable.