So the night really does look like:

We don’t see it because of light pollution these days… these days we see a black night punctured by a few stars.

Before the light pollution started to really hit the sky, Van Gogh painted his most famous work, “The Starry Night”:

So the swirls aren’t clouds—they’re clouds of stars, a galaxy or the Milky Way crossing the sky or similar. He painted this scene from memory as well, so there’s an extra layer of interpretation to go through, I suppose… but now I think the painting is quite beautiful.