Wild guess what the "seven skies" might be :
1st sky : earth atmosphere. which creates the blue sky we see at day time.
2nd sky : orbit around the earth. Which includes our moon. That way when we read Jinns travel to the border of the first sky where they are stoned back, that might mean travel up to the height of the atmosphere. And the matroid stones that starts to burn as soon as they hit the atmosphere.
3rd sky : orbit around the sun. Which includes all the planets and our solar system. Nothing has left the 3rd sky. Voyager questionably.
4th sky : our galaxy. basically all the stars we see above the sky. By that explanation the saying that goes like "Jesus is in the 4th sky" might mean he is in another planet orbiting another star in our galaxy.
5th sky : visible universe. Including all the galaxies. Inter galactic travel is impossible even in science fictions. All the stories we read are interstellar. Stars within our galaxy. The vastness of the visible universe is unfathomable. One can read the numbers but can't just grok it.
6th sky : other universes like ours. Created from other big bangs. The multi-verse theory. Note that multi-verse in Quantum mechanics and multi-verse in big bang are difference things. I don't believe in QM multi-verse. By the way, there is no way to detect the other universes, let alone a physical way to travel to those.
7th sky : we have no understanding on what that it.
Just a theory.
Counter arguments :
"All the visible stars are in 1st sky as said in a hadith."