 In HM, Kepler continues his investigations of the polyhedra at a cosmological as well as a mathematical level. In the second book, dealing with “congruence” (which here does not mean, as it does today, “the same size and shape”, but the property of figures filling the surface together with other regular polygons – on the plane—or, to build closed geometric solids – hence, in space), Kepler made new mathematical discoveries working with tessellations. He discovered two new solids, the so-called “small and great stellated dodecahedrons”.