Earlier quoted context omitted.
I don't think it's nonsensical. There is a meaningful way in which it is in the past. Even if you turn yourself into photons, match positions with the supernova remnants, then return to physical form, the supernova is going to evolve though time for quite a ways beyond the current state we observe it in before your physical form has its rendezvous, even if the trip has zero duration for you. Putting a specific time s…
If you set a reference point, then I think it's perfectly sensical to say two events happen simultaneously or "now," but without a set reference point those notions are completely nonsensical. Most educated people understand the principle of relativity (which states that the laws of physics behave consistent in all frames of reference) and the fact that the speed of light is constant regardless of your frame of refer…
Only in the case that neither A can observe B nor B can observe A, which we denote by saying that the events are in their relative present, the ordering becomes relative to the frame of refrence, but that case is irrelevant in the present discussion, as we can observe the nova and so have established the fact that it (or at least its beginning) is in our past. Note that its maximum, which is predicted to be observable around next friday, is in our present (we can not influence nor observe it yet), while our observation of it is in our future (we can still make plans for where to watch it), at least until next friday, when both of these events simultaneously move into our past.