Ok, imagine this experiment: I am in Mars, inside of a supersonic storm. There is a small sphere standing inside the incident flow, and I am in a laboratory viewing the shock wave caused by the sphere. I have some pressure measurements of the flow, (i.e around of the sphere surfice), so I can demostrate the shock wave presence. At this point, I have the idea of choosing a different reference frame for extracting measurements. I choose just a reference frame where I can see the flow being completely subsonic (i.e. the laboratory translates at some speed so that viewing is possible, by means of a galilean velocity composition). If the flow is subsonic, no shock wave will be seen at all. I suppose (certainly?) that static pressure and entropy measurements are not a function of the reference frame chosen, so I will have the same experimental figures of the first case, where the flow was supersonic. I mean, in some reference frame I will see a shock wave, and in another I will not see one. But we know that a fluid throug shock waves have an increasing in its entropy and a strong pressure loss. This two properties are not a function of a reference frame, because are local thermodynamic properties of the flow. What happens? Is there a shock wave? How could I demostrate that in these two laboratories?