An angle symbolized beta describing this property has a value of about 0.30 according to Planck data, a non-zero value of which would be a signature of parity-violating physics. This property is represented by the two quantities that take on non-zero values (-5[1])in the transverse-traceless gauge. In 2002, the DASI (“daisy”) telescope was used to observe a component of this property that originates from Thomson scattering. Scalar (*) fluctuations and gravitational waves are respectively sources of the irrotational and solenoidal components of this property, which are named in analogy to the electric and magnetic fields. Intergalactic magnetic fields rotate the plane of this property in an example (10[1])of the Faraday effect. For 10 points, name this property of the cosmic microwave background, (10[1])the direction in which electromagnetic waves oscillate. (10[1])■END■