Bilunabirotunda | |
---|---|
![]() | |
Type | Johnson J90 – J91 – J92 |
Faces | 8 triangles 2 squares 4 pentagons |
Edges | 26 |
Vertices | 14 |
Vertex configuration | 4(3.52) 8(3.4.3.5) 2(3.5.3.5) |
Symmetry group | |
Properties | convex, elementary |
Net | |
![]() |
In geometry, the bilunabirotunda is a Johnson solid with faces of 8 equilateral triangles, 2 squares, and 4 regular pentagons.
The bilunabirotunda is named from the prefix lune, meaning a figure featuring two triangles adjacent to opposite sides of a square. Therefore, the faces of a bilunabirotunda possess 8 equilateral triangles, 2 squares, and 4 regular pentagons as it faces. [1] It is one of the Johnson solids —a convex polyhedron in which all of the faces are regular polygon —enumerated as 91st Johnson solid . [2] It is known as the elementary polyhedron, meaning that it cannot be separated by a plane into two small regular-faced polyhedra. [3]
The surface area of a bilunabirotunda with edge length is: [1] and the volume of a bilunabirotunda is: [1]
One way to construct a bilunabirotunda with edge length is by union of the orbits of the coordinates under the group's action (of order 8) generated by reflections about coordinate planes. [4]
Reynolds (2004) discusses the bilunabirotunda as a shape that could be used in architecture. [5]
Six bilunabirotundae can be augmented around a cube with pyritohedral symmetry. B. M. Stewart labeled this six-bilunabirotunda model as 6J91(P4). [6] Such clusters combine with regular dodecahedra to form a space-filling honeycomb.
![]() | ![]() Spacefilling honeycomb | ![]() 6 bilunabirotundae around a cube | 12 bilunabirotundae around a dodecahedron |