Question

How do astronomers measure polarization

Answer 1

Both circular and linear polarization of light from the Sun has been measured. Circular polarization is mainly due to transmission and absorption effects in strongly magnetic regions of the Sun's surface. Another mechanism that gives rise to circular polarization is the so-called alignment-to-orientation mechanism. Continuum light is linearly polarized at different locations across the face of the Sun though taken as a whole, this polarization cancels. Linear polarization in spectral lines is usually created by anisotropic scattering of photons on atoms and ions which can themselves be polarized by this interaction. The linearly polarized spectrum of the Sun is often called the second solar spectrum.