sophiecentaur said:It is always that way from my viewpoint.
I was describing a "global" viewpoint using a frame centered on the barycenter of the solar system. In my exchanges with @DrStupid I have been giving reasons why that frame is the right one for describing orbits, at least if we want to include the Sun as well as the Earth and Moon in our description.
Of course "right" here is ultimately a matter of preference; nothing forces you to use such a frame. And if you insist on using a different frame, yes, the trajectories of objects will look different (but that assumes that the frame covers a given object's trajectory; note my remarks about the Sun not being covered by Fermi normal coordinates centered on the Earth). But the reasons I am giving for why the frame I suggest is the "right" one are not arbitrary; they are based on physical facts about the particular situation being described.
sophiecentaur said:Imagine you are in a craft, orbiting the Moon. How would you describe things - assuming you knew nothing about modern astronomy?
Nothing requires you to use a frame in which you, or the particular object you are orbiting (or think you are orbiting), is at rest. So in the case you describe, you could use the frame I have been suggesting, centered on the barycenter of the solar system, just fine.