Bicupola (geometry)

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Set of bicupolae
Cuboctahedron.svg
Example: triangular gyrobicupola (cuboctahedron)
Faces 2n triangles,
2n squares
2 n-gons
Edges 8n
Vertices 4n
Symmetry group Ortho: Dnh, [2,n], *n22, order 4n
Gyro: Dnd, [2+,2n], 2*n, order 4n
Properties convex
The gyrobifastigium (J26) can be considered a digonal gyrobicupola. Gyrobifastigium.png
The gyrobifastigium (J26) can be considered a digonal gyrobicupola.

In geometry, a bicupola is a solid formed by connecting two cupolae on their bases.

Contents

There are two classes of bicupola because each cupola (bicupola half) is bordered by alternating triangles and squares. If similar faces are attached together the result is an orthobicupola; if squares are attached to triangles it is a gyrobicupola.

Cupolae and bicupolae categorically exist as infinite sets of polyhedra, just like the pyramids, bipyramids, prisms, and trapezohedra.

Six bicupolae have regular polygon faces: triangular, square and pentagonal ortho- and gyrobicupolae. The triangular gyrobicupola is an Archimedean solid, the cuboctahedron; the other five are Johnson solids.

Bicupolae of higher order can be constructed if the flank faces are allowed to stretch into rectangles and isosceles triangles.

Bicupolae are special in having four faces on every vertex. This means that their dual polyhedra will have all quadrilateral faces. The best known example is the rhombic dodecahedron composed of 12 rhombic faces. The dual of the ortho-form, triangular orthobicupola, is also a dodecahedron, similar to rhombic dodecahedron, but it has 6 trapezoid faces which alternate long and short edges around the circumference.

Forms

Set of orthobicupolae

Symmetry PictureDescription
D2h
[2,2]
*222
Digonal orthobicupola.png Orthobifastigium or digonal orthobicupola: 4 triangles (coplanar), 4 squares. It is self-dual
D3h
[2,3]
*223
Triangular orthobicupola.png Triangular orthobicupola (J27): 8 triangles, 6 squares; its dual is the trapezo-rhombic dodecahedron
D4h
[2,4]
*224
Square orthobicupola.png Square orthobicupola (J28): 8 triangles, 10 squares
D5h
[2,5]
*225
Pentagonal orthobicupola.png Pentagonal orthobicupola (J30): 10 triangles, 10 squares, 2 pentagons
Dnh
[2,n]
*22n
n-gonal orthobicupola: 2n triangles, 2n rectangles, 2 n-gons

Set of gyrobicupolae

A n-gonal gyrobicupola has the same topology as a n-gonal rectified antiprism, Conway polyhedron notation, aAn.

Symmetry PictureDescription
D2d
[2+,4]
2*2
Gyrobifastigium.png Gyrobifastigium (J26) or digonal gyrobicupola: 4 triangles, 4 squares
D3d
[2+,6]
2*3
Cuboctahedron.png Triangular gyrobicupola or cuboctahedron: 8 triangles, 6 squares; its dual is the rhombic dodecahedron
D4d
[2+,8]
2*4
Square gyrobicupola.png Square gyrobicupola (J29): 8 triangles, 10 squares;its dual is the elongated tetragonal trapezohedron
D5d
[2+,10]
2*5
Pentagonal gyrobicupola.png Pentagonal gyrobicupola (J31): 10 triangles, 10 squares, 2 pentagons; its dual is the elongated pentagonal trapezohedron
Dnd
[2+,2n]
2*n
n-gonal gyrobicupola: 2n triangles, 2n rectangles, 2 n-gons

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References