Assuming spacetime is not expanding, let's say 1 galaxy is moving away from us at .9c. I leave our galaxy and catch it by travelling at .99c. Then a citizen of

Assuming spacetime is not expanding, let's say 1 galaxy is moving away from us at .9c. I leave our galaxy and catch it by travelling at .99c. Then a citizen of that galaxy, at rest, accelerates to .9c. So his velocity relative to earth is .89c? I think I need to go watch a youtube video on special relativity. Intertial reference frames are really weird.