And yes, I agree that it's absurd. The Death Star is basically a giant spherical capital ship, so having it fly around from place to place nuking planets is plausible (if you can accept that things like hyperspace and artificial gravity and ray shields and so on are things that exist).
Or the Force. *cough*
Star Wars isn't science-fiction. Pulling sufficient energy to dim a star through a planet would instantly vaporize the planet. But if this is what a film presents, it's not unreasonable to assume that laws-of-physics-defying fantasy technology exists in-universe to move a planet around.