Adrian Price-Whelan and I met with some prospective undergraduate researchers, Abi Polin and Layla Quinones, to look at computational photography things; they are both amateur photographers. We discussed the baby steps towards doing some calibration of commercial digital cameras.
In the afternoon, Scott Hughes (MIT) brought us up to date on the two-body problem in general relativity, where there has been enormous progress in the six years or so since his last visit. He showed that the leading-order Newtonian approximation of GR contains a gravitometric term, which (in my opinion) should have been discovered way before GR: It permits the speed of gravity to be finite but objects to continue in Keplerian orbits! Hughes's talk was not particularly about this, but I have been thinking about it ever since I read Sciama's excellent (out of print) book.