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Stokes parameters are values that describe polarization of electromagnetic radiation. They were developed by George Gabriel Stokes in 1852. Different versions exist, all equivalent to four scalar values that indicate a three-dimensional vector regarding the direction of polarization and a fourth to distinguish between the EMR's intensity and its (fractional) degree of polarization. In one commonly-used version (Cartesian coordinates), they are called I, Q, U, and V where I is the intensity of the beam and the others indicating the geometry of the polarization. The four are also sometimes labeled S1 through S4 (for I, Q, U, and V, but confusingly, the labels S0 through S3 are also sometimes used). A Stokes map is a map of a portion of the celestial sphere indicating the values over the extent of the map of one or more Stokes parameter.