In 1951, 1962, and 1981, Swiss astronomer Louis Jacot, like Weizsäcker and Ter Haar, continued the Cartesian idea of vortices but proposed a hierarchy of vortices, or vortices within vortices, i.e. a lunar system vortex, a Solar System vortex, and a galactic vortex. He put forward the notion that planetary orbits are spirals, not circles or ellipses. Jacot also proposed the expansion of galaxies in that stars move away from the hub and moons move away from their planets.