Parallax is the name of the phenomenon whereby when something is far away, it appears to be moving more slowly than something nearby moving at the same speed. It’s one of those phenomena that make perfect intuitive sense but very little logical sense. Or vice versa; I don’t know.

A plane crossing the sky at 600 mph covers less space in your visual field per second than does an old granny walking by your porch at 1 mph and appears to be moving more slowly. That concept is obviously true, but it’s hard to explain why.

I have nothing more to say on this matter.