I have read things like if the sun disappeared, it would take 8 minutes or so before we knew this, cf. e.g. this Phys.SE post.
However, in real life the sun will never disappear and if it exploded, its center of mass would remain more or less the same anyway.
So what real life experiment or phenomenon reveals the speed of gravity?
If you had a very heavy mass and moved it using very sensitive equipment to detect this movement via change in gravitational attraction, would not the movement of the mass have to be a the speed of light or near it to prove that gravity propagated at the speed of light? Or is there in fact some experiment like that where a mass is moved at fairly slow speed to establish the speed of gravity?
EDIT: It seems to me that light-speed measurement is accomplished most easily by turning off and on a source or blocking a light source neither of which can be done with gravity.
EDIT 2: I think I am not understanding how the experiments work. How does a massive object in motion allow one to determine the speed of gravity since this motion is continuous? That is, the object is not suddenly some large distance away from where it was -- I could understand as previously indicated that if a mass was created from nothing somehow, one could watch how long this new source of gravity took to affect an existing mass but if the mass is merely moving relative to another mass, I can't visualize how this can be used to measure the speed of gravity which is always affecting the second mass, just slightly less so if the as the objects move apart.