Cambrian.

You FIRST see it, then you HEAR it. The time delay depends on your distance from the source of the explosion. The explanation, light travels faster than sound.

A neutron star, or a black hole. Which it is, depends on the mass that remains after the supernova explosion. Above a certain mass limit, a black hole will form.

It depends how big the explosion is.

A stick of dynamite exploding on the moon would obviously not be visible to a naked eye on Earth, but a 100 Megaton hydrogen bomb might be.

the explosion = die Explosion.