  Kostelecky and Mewes have recently shown that sensitive constraints can be
placed on some aspects of Lorentz symmetry violation using certain astronomical
data on high-redshift sources. Here, I introduce that data in its astronomical
context, making it clear that these data are robust and accurate for their
purpose. In particular, I explain that spatially extended scattered light from
obscured quasars leads to a centrosymmetric scattering polarization, with
polarization position angle independent of wavelength. Evidentally, these
relationships aren't spoiled by propagation effects as the photons cross the
universe.
