Wavelength dependence of the polarization of the continuum (left) and depolarization in the spectral lines (right) under different approximations. On the left are shown the polarization of simple Rayleigh scattering by hydrogen atoms (blue), the approximation λ^-4 (green), and the empirical law from Fluri & Stenflo (1999) for the continuum of the Sun taking into account the chromatic dependence of limb darkening (red). On the right is shown depolarization in the lines, without taking into account the chromatic variation of limb darkening (achromatic illumination, green curve), or including this variation as in the solar case (blue). Points are the maxima of the main polarization peak represented in Fig. 5 with their error bars, together with the power law λ^-1 (red).