  The solar corona and heliosphere are visible via sunlight that is
Thomson-scattered off of free electrons, yielding a radiance against the
celestial sphere. In this second part of a three-article series, we discuss
linear polarization of this scattered light parallel and perpendicular to the
plane of scatter in the context of heliopheric imaging far from the Sun. The
difference between these two radiances, (pB), varies quite differently with
scattering angle, compared to the sum that would be detected in unpolarized
light (B). The difference between these two quantities has long been used in a
coronagraphic context for background subtraction and to extract some
three-dimensional information about the corona; we explore how these effects
differ in the wider-field heliospheric imaging case where small-angle
approximations do not apply. We develop an appropriately-simplified theory of
polarized Thomson scattering in the heliosphere, discuss signal-to-noise
considerations, invert the scattering equations analytically to solve the three
dimensional object location problem for small objects, discuss exploiting
polarization for background subtraction, and generate simple forward models of
several classes of heliospheric feature. We conclude that pB measurements of
heliospheric material are much more localized to the Thomson surface than are B
measurements, that the ratio pB/B can be used to track solar wind features in
three dimensions for scientific and space weather applications better in the
heliosphere than corona; and that, by providing an independent measurement of
background signal, pB measurements may be used to reduce the effect of
background radiances including the stably polarized zodiacal light.
