'Sky' in the Bible

In the same region there were shepherds staying out in the fields, keeping watch over their flock by night.

You hypocrites (play-actors, pretenders)! You know how to analyze and intelligently interpret the appearance of the earth and sky [to forecast the weather], but why do you not intelligently interpret this present time?

For just like the lightning, when it flashes out of one part of the sky, gives light to the other part of the sky, so [visible] will the Son of Man be in His day.

Heaven and earth will pass away, but My words will not pass away.