  The propagation of plane electromagnetic waves in the gravitational field
inside a rotating cloud of dark matter is analyzed. Formulas for the deflection
and absorption of light, and the rotation of the polarization plane are
obtained in closed form in terms of the mass density and the angular velocity
of the cloud. It is shown that the formulas can be considerably simplified for
axisymmetric configurations. As an example, the formalism is applied to a
rotating massive cloud described by a Plummer potential.
