As part of my project with Adrian Price-Whelan (and also Melissa Ness and Dan Foreman-Mackey), I spent my research time today figuring out time derivatives of Kepler's equations. These so we can do simultaneous fitting of the eclipsing binary light curve and the radial velocities revealed in the double-line spectrum. This was actual pen-on-paper calculus! It's been a while, although as I took these derivatives, it reminded me that I have taken them many times in the past.
In the afternoon I had a great conversation with Duane Lee (Vanderbilt) about chemical tagging and nucleosynthesis. He is close to being able to fit our data in the Milky Way halo with a mixture of dwarf-galaxy stellar populations. That would be awesome! We talked about low-hanging fruit with our APOGEE chemical abundance data.