Astronomy Colloquium

I present proper motions for the Large & Small Magellanic Clouds (LMC & SMC) based on three epochs of Hubble Space Telescope data, spanning a $\sim 7$ yr baseline, and centered on background QSOs. The first two epochs are provided by the ACS/HRC and were the subject of Kallivayalil et al. (2006a,b) but have been reanalyzed here. The third epoch is brand new data taken with the WFC3/UVIS, providing a completely independent check. Due to the longer timebaseline and the high quality of the WFC3 data we derive proper motions of high accuracy. We are therefore also able to derive a purely proper motion-based rotation curve for the LMC, which is in excellent agreement with the latest line-of-sight velocity-based studies, and for the first time, competitive with the kinds of accuracies typically quoted in such studies. We determine the rotation velocity at large radii a factor of 3 more accurately than previous work. I discuss the consequences of these new measurements for our understanding of the global dynamics of the Milky Way-LMC-SMC system. This work is part of a larger effort towards 6-D mapping of the Milky Way.