Understanding astronomical objects requires knowledge and methods from different branches of theoretical physics: we diagnose these objects mostly by the light we receive; the observed phenomena often have to do with the flow of fluids, sometimes ionised, sometimes magnetised; and the measured velocities reflect dynamics driven by gravitational fields. Courses in theoretical physics lay the foundation in classical and quantum mechanics, electrodynamics, and thermodynamics, but a gap remains between this foundation and its application to astrophysics. These lecture notes build upon the core...