I have read, if the sun disappeared it would take 8 minutes before this could be detected on Earth due to speed of gravity being $c$. Of course, the sun can't disappear. Perhaps realizing this impossibility, people write of the sun exploding instead. But if the sun literally exploded the mass would still be present for a while, just dispersed.
So what actual physical event would allow us to observe the speed of gravity? If rotating massive objects, how? And if the sun exploding would allow this observation, how so?