Kuhn's latest account locates incommensurability as a mismatch between taxonomies of natural kind terms. In collaboration with Hanne Andersen (University of Copenhagen) and Xiang Chen (California Lutheran University) I have developed a more general account along the same lines using the dynamic frame notation introduced by cognitive psychologist Lawrence Barsalou (Emory University, Atlanta). Here I apply a simplified version of this model to the conceptual systems of Ptolemaic, Copernican and Keplerian astronomy. I conclude that Copernicus's astronomy is only minimally incommensurable with Ptolemy's, but that Kepler's is strongly incommensurable with both.