Stellated octahedron  

Type  Regular compound 
Stellation core  Octahedron 
Convex hull  Cube 
Index  UC_{4}, W_{19} 
Polyhedra  2 tetrahedra 
Faces  8 triangles 
Edges  12 
Vertices  8 
Dual  Selfdual 
Symmetry group  octahedral (O_{h}) 
Subgroup restricting to one constituent  tetrahedral (T_{d}) 
The stellated octahedron, or stella octangula, is the only stellation of the octahedron. It was named by Johannes Kepler in 1609, though it was known to earlier geometers. It was depicted in Pacioli's Divina Proportione, 1509.
It is the simplest of five regular polyhedral compounds.
It can be seen as either a polyhedron compound or a stellation:
As a compound, it is constructed as the union of two tetrahedra (a tetrahedron and its dual tetrahedron). The vertex arrangement of the two tetrahedra is shared by a cube. The intersection of the two tetrahedra form an inner octahedron, which shares the same faceplanes as the compound.
It can be seen as an octahedron with tetrahedral pyramids on each face. It has the same topology as the convex Catalan solid, the triakis octahedron, which has much shorter pyramids.
The stellation facets are very simple: (See Wenninger model W_{19}.)
