'Sky' in the Bible

And as they were staring into the sky [while] he was departing, behold, two men in white clothing stood by them

who also said, "Men {of Galilee}, why do you stand there looking into the sky? This Jesus who was taken up from you into heaven like this will come back in the same way you saw him departing into heaven!"

in which were all the four-footed animals and reptiles of the earth and birds of the sky.

[As I] looked intently into it, I was considering [it], and I saw the four-footed animals of the earth and the wild animals and the reptiles and the birds of the sky.