Although there are no iron filings on the Sun to outline the magnetic field for us,
there are other ways to know it is there. Spots on the surface of the Sun are
one sign of the magnetic field. The Sun's magnetic field hinders the usual
boiling motion which mixes the hot and cool gasses in the photosphere. In the
strong magnetic regions the cooler gas becomes trapped, and appears as a
dark spot on the solar surface.
Image Credit: Big Bear Solar Observatory