Switched back and forth between multi-tweak and sky-subtraction issues with Moustakas and Local-Group galaxy data issues with Willman. With Moustakas we have gotten a long way towards a full implementation of "hizzle", which is my replacement for STScI drizzle, but with a much better philosophy (in my opinion) about what an image is. Unfortunately, Emmanuel Bertin's "swarp" code does (almost) everything our hizzle does and some things hizzle doesn't, so I am not sure this is a good use of our time. On the other hand, we both love data reduction!
I discussed cosmic transparency with high-schooler Nick Makarov. There are a few wacky ideas about the dark sector out there that are strongly constrained by transparency, as measured from present-day observations of distant sources; but no-one has spent the time to work out the limits.