Is the Universe transparent? This issue has been interesting me for many years; the answer is "yes" of course, but just how transparent? There are many ways to look at transparency, but a talk by Corrales last week got me thinking about it again: Take some point sources, regress their images against brightness, color, and line-of-sight dust amplitude. Do you see a scattering halo that is correlated with dust? In the optical and UV, I think you won't, based on unpublished work I have done previously. However, there might be a tiny signal. Also, there is more likely to be an effect in the x-ray, which (with Chandra) is accessible. And there is abundant archival data for this project in every waveband from infrared to X-ray.
