Pentagonal cupola

Pentagonal cupola
Type	Johnson J4 - J5 - J6
Faces	5 triangles 5 squares 1 pentagon 1 decagon
Edges	25
Vertices	15
Vertex configuration	10(3.4.10) 5(3.4.5.4)
Symmetry group	C5v, [5], (*55)
Rotation group	C5, [5]^+, (55)
Dual polyhedron	-
Properties	convex
Net

In geometry, the pentagonal cupola is one of the Johnson solids (J₅). It can be obtained as a slice of the rhombicosidodecahedron. The pentagonal cupola consists of 5 equilateral triangles, 5 squares, 1 pentagon, and 1 decagon.

A Johnson solid is one of 92 strictly convex polyhedra that have regular faces but are not uniform (that is, they are not Platonic solids, Archimedean solids, prisms or antiprisms). They were named by Norman Johnson, who first listed these polyhedra in 1966.^[1]

Formulae

The following formulae for volume, surface area and circumradius can be used if all faces are regular, with edge length a:^[2]

$V=\left(\frac{1}{6}\left(5+4\sqrt{5}\right)\right)a^3\approx2.32405...a^3$

$A=\left(\frac{1}{4}\left(20+5\sqrt{3}+\sqrt{5(145+62\sqrt{5})}\right)\right)a^2=\left(\frac{1}{4}\left(20+\sqrt{10\left(80+31\sqrt{5}+\sqrt{15(145+62\sqrt{5})}\right)}\right)\right)a^2\approx16.5797...a^2$

$C=\left(\frac{1}{2}\sqrt{11+4\sqrt{5}}\right)a\approx2.23295...a$

Related polyhedra

Dual polyhedron

The dual of the pentagonal cupola has 10 triangular faces and 5 kite faces:

Dual pentagonal cupola	Net of dual

Other convex cupolae

Family of convex cupolae

n	2	3	4	5	6
Name	{2} || t{2}	{3} || t{3}	{4} || t{4}	{5} || t{5}	{6} || t{6}
Cupola	Digonal cupola	Triangular cupola	Square cupola	Pentagonal cupola	Hexagonal cupola (Flat)
Related uniform polyhedra	Triangular prism	Cubocta- hedron	Rhombi- cubocta- hedron	Rhomb- icosidodeca- hedron	Rhombi- trihexagonal tiling

Crossed pentagrammic cupola

In geometry, the crossed pentagrammic cupola is one of the nonconvex Johnson solid isomorphs, being topologically identical to the convex pentagonal cupola. It can be obtained as a slice of the nonconvex great rhombicosidodecahedron or quasirhombicosidodecahedron, analogously to how the pentagonal cupola may be obtained as a slice of the rhombicosidodecahedron. As in all cupolae, the base polygon has twice as many edges and vertices as the top; in this case the base polygon is a decagram.

It may be seen as a cupola with a retrograde pentagrammic base, so that the squares and triangles connect across the bases in the opposite way to the pentagrammic cuploid, hence intersecting each other more deeply.

References

1. Johnson, Norman W. (1966), "Convex polyhedra with regular faces", Canadian Journal of Mathematics 18: 169–200, doi:10.4153/cjm-1966-021-8, MR 0185507, Zbl 0132.14603.
2. Stephen Wolfram, "Pentagonal cupola" from Wolfram Alpha. Retrieved July 21, 2010.

External links

• Eric W. Weisstein, Pentagonal cupola (Johnson solid) at MathWorld