Polarization in astronomy

Polarization is an important phenomenon in astronomy. The polarization of starlight was first observed by the astronomers William Hiltner and John S. Hall in 1949. Subsequently, Jesse Greenstein and Leverett Davis, Jr. developed theories allowing the use of polarization data to trace interstellar magnetic fields. Although the thermal radiation of stars in not appreciably polarized at source, its scattering by interstellar dust imposes polarization on starlight over long distances. Circular polarization of light from the Sun has, however, been measured; it is due to transmission and absorption effects in strongly magnetic regions of the Sun's surface. Plane polarization of starlight generated at the star itself is also observed for Ap stars (peculiar A type stars) [1]