A question for this space ignoramus:
Just exactly what makes the boundary between heliosphere and interstellar medium a "shock", and why does it appear to occupy such large distance?
I guess the intuition (sure reliable, eh?
) would have been that solar winds would gradually fizz out and given the vastness of space involved, it seems odd to imagine there's a "shock".
Have I made the mistake of assuming that interstellar medium = void?
Or is it just a poor choice of wording like "annihilating particle" which actually doesn't violate the conservation of mass/energy?