synthesize the entire SDSS

After a long hiatus Lang and I resumed our quasi-regular Skype calls to discuss The Tractor and publications thereof. We sure are taking a long time to deliver! Lang proposed a brilliant de-scope that permits a paper to be written in short order without much additional engineering beyond what we have already done: Let's write a paper in which we synthesize (make model images for) every SDSS field imaged to date, in all five bands, and do investigations on the residuals. Investigations can include goodness-of-fit-like statistics but also overlap of the residuals with derivatives of the model with various parameters (like object positions, fluxes, and shapes). The idea would be to use the official SDSS catalog and calibration parameters (astrometry, PSF, photometric zeropoints) without analysis, so that the synthesis would be a full-survey vet of the full system. The fundamental assumption is that the catalog is a set of model parameters that describe quantitatively the data. That would be fun, and show that we can do something, at least, at scale. I also had interesting conversations with Tom Robataille (MPIA) about astropy and the future of data analysis, and Kapala about ultraviolet HST data and dust.