structural:summarization, information:extraction
Polarization

The cosmic microwave background is polarized at the level of a few microkelvin. There are two types of polarization, called E-mode (or gradient-mode) and B-mode (or curl mode). This is in analogy to electrostatics, in which the electric field (E -field) has a vanishing curl and the magnetic field (B -field) has a vanishing divergence.