Set of birotundas | |
---|---|
(Example Ortho/gyro pentagonal forms) | |
Faces | 2 n-gons 2n pentagons 4n triangles |
Edges | 12n |
Vertices | 6n |
Symmetry group | Ortho: D_{nh}, [n,2], (*n22), order 4n Gyro: D_{nd}, [2n,2^{+}], (2*n), order 4n |
Rotation group | D_{n}, [n,2]^{+}, (n22), order 2n |
Properties | convex |
In geometry, a birotunda is any member of a family of dihedral-symmetric polyhedra, formed from two rotunda adjoined through the largest face. They are similar to a bicupola but instead of alternating squares and triangles, it alternates pentagons and triangles around an axis. There are two forms, ortho- and gyro-: an orthobirotunda has one of the two rotundas is placed as the mirror reflection of the other, while in a gyrobirotunda one rotunda is twisted relative to the other.
The pentagonal birotundas can be formed with regular faces, one a Johnson solid, the other a semiregular polyhedron:
Other forms can be generated with dihedral symmetry and distorted equilateral pentagons.