Polarimetry allows the observation of symmetries being broken in astrophysical objects. Whether it is because of the presence of a magnetic field vector or because light coming from a preferred direction is scattered or because the scattering of light happens on an atom or dust or body that has lost its spherical shape, the appearance of a privileged direction in space always results in the emission of polarized light. 

Those privileged directions carry information on the physics taking place at the source of light and astronomers want to learn about it. The observation and measurement of polarization happens therefore in all astronomical objects being observed: the Sun, the planets and their atmospheres, those of our solar system and those of other extra-solar systems, stars either magnetized or non-spherical, disks and jets around those stars or around black holes in active galactic nuclei, dust on planets, in comets, or in the interstellar medium and finally the universe as a whole can have preferred directions available through the polarization of the microwave cosmic background.

The observation and measurement of polarization also happens in all kinds of electromagnetic radiation: from radio, through microwaves, into the infrared and visible spectrum of the light and all the way into the energetic X-rays. 

Expertise and know-how on this measurement is therefore scattered through different astronomical communities, limited in the objects and in the wavelengths observed. Techniques, calibrations, procedures are therefore often very similar but re-invented again and again in every possible subfield.

It is the primary goal of WG1 to collect and share expertise in polarimetry throughout communities concerned with different objects and different wavelengths. To this purpose, lists of groups involved in polarimetry will be created as well as resources to find techniques, calibrations, and procedures of polarimetry as they are applied in all those different fields. We expect this to result in new ideas as techniques are being exported from one field to the other and new collaborations as people meet to share their experiences and their know-how.