H i temperature parallel to the magnetic field lines as a function of the heliocentric distance derived from measurements of T_⊥ during the minimum phase of the solar activity cycle. Plots show the results at the different angular sectors separated by 45 degrees counterclockwise from the solar north pole (0° PA). The range of feasible T_∥ values (shaded area) is delimited by the conditions of maximum anisotropy (red line) and isotropy (blue line).