Surface Polarimetry of the Milky Way

Abstract

Two methods of determining the state of polarization of the integrated light from the Milky Way are discussed. In the symmetry method it is assumed that the polarized foreground zodiacal light possesses north/south symmetry relative to the ecliptic: an average polarized intensity of at least 10 S ₁₀(R) is derived for the Milky Way at l ≃ 90° and 270°, which is consistent with the result of Sparrow and Ney (1972) who obtained 18 S₁₀ (R) at l = 35° and 210°. In the method of two epochs the above assumption is not needed but instead time variations of the zodiacal light are assumed to be insignificant: the results obtained by this method (in S ₁₀ (V) units), although compatible with the values found by the symmetry method, do however show that time variations may have influenced this result. Although the evidence for a definite polarization of the Milky Way is persuasive it cannot yet be considered conclusive.