The Sun as a star

The Sun and the theory of stellar structure, solar rotation, the solar cycle, and the solar magnetic field are discussed. The validity of solar models which adjust Prandtl's mixing length and helium abundance so that radius and luminosity match their solar values is tested. The fragmentary state of turbulence theory prevents investigation of the hydrogen convection zone from providing quantitative validation. Evidence based on solar neutrino flux and nonradial solar oscillations is not decisive. The transport of angular momentum towards the equator, resulting in differential rotation, could be due to anisotropic viscosity caused by turbulent eddies in the convection zone, Rossby waves, or convection. The pairwise appearance of sunspots and their migration towards lower latitudes are accounted for in numerical solutions of the modified induction equation. These show that strong toroidal flux tubes, of opposite sign in each half cycle, are produced.