Polarization in astronomy

Polarization in astronomy is the measurement and interpretation of the orientation and degree of polarization in radiation from celestial sources. It reveals properties of emitting matter, magnetic fields, scattering environments, and propagation through space.

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Stokes parameters: Four quantities that describe the intensity and polarization state of electromagnetic radiation. They provide the standard measurements used to quantify astronomical polarization.
Cosmic microwave background polarization: The polarized component of the cosmic microwave background produced by early-universe scattering and later foreground effects. Its patterns constrain cosmological parameters and the history of cosmic structure.
Linear polarization: A polarization state in which the electric field oscillates along a fixed direction perpendicular to propagation. Astronomical polarization studies commonly map its orientation and fractional strength.
Unpolarized light: Light whose polarization direction varies randomly or whose polarization components average to zero. It is the limiting comparison for detecting a polarized component in astronomical radiation.
Synchrotron radiation: Radiation emitted by relativistic charged particles spiraling in magnetic fields. Its polarized emission traces magnetic-field structure in many astronomical sources.
Solar magnetic field: The magnetic field generated and structured within the Sun and extending into interplanetary space. Solar spectropolarimetry infers its strength and orientation from Zeeman-sensitive signals.
Polarimetry: The measurement of the polarization state of electromagnetic radiation. Astronomical polarization is obtained through this broader measurement discipline.
Circular dichroism: Differential absorption of left- and right-circularly polarized radiation by a medium. It differs from the linear dichroic extinction that commonly polarizes interstellar starlight.
Thomson scattering: Elastic scattering of electromagnetic radiation by free charged particles at low photon energies. Scattering by electrons generates polarization in sources such as stellar atmospheres and accretion flows.
Magnetic fields in star-forming regions: Magnetic fields within molecular clouds and environments where stars form. Dust polarization maps their projected geometry and its relation to collapsing gas.