Fun also-fact, (at least in Boom ports) if you scroll the wall texture, the sky will scroll as well.

You can use linked scrollers to create an illusion of movement too. I used this to create a switch that accelerated and then "moved" a spaceship by progressively scrolling the sky outside the windows more and more until it looked like you were "up to speed". I could have also had it slow down and stop but that wasn't necessary in my case.