The scattering geometry. This figure shows the scattering geometry at the scatterer (i.e., point P of Fig. 3). The angles and are the spherical polar angles in the stellar coordinate system. The angles θ and δ are in the coordinate system for which the magnetic field direction is the local z‐axis. The angles i_i and i_s are the Mueller rotation angles used to rotate the Stokes vectors to and from the local coordinates of the magnetic field to those of the observer's measurement axes. The subscripts i, s, and B refer to the incident radiation, the scattered radiation, and the magnetic field, respectively. The scattered intensity I_s is parallel to the observer's Z‐axis. Finally, χ is the angle between the incident and scattered intensity rays.