On what does the apparent motion of objects in the sky depend?

It depends on the objects that are seen near it. it is called reletive motion exg
if your father is driving you home from your friend's house and your friend is outside waving at you, your friends appears to be moving away, but your father does not since he is moving at the same speed as you are and is not moving reletive to you

so if there is a cloud in  the sky without anything near it, it probably looks moving slowly
if there are buildings near it. it probably looks to be going fast