  The orbital angular momentum (OAM) of light is potentially interesting for
astronomical study of rotating objects such as black holes, but the effect of
reduced spatial coherence of astronomical light sources such as stars is
largely unknown. In a lab-scale experiment, we find that the detected OAM
spectrum depends strongly on the position of the light-twisting object along
the line of sight. We develop a simple intuitive model to predict the influence
of reduced spatial coherence in astronomical observations, and discuss
line-of-sight and intensity issues.
