From Wikipedia, the free encyclopedia

Truncated icosahedron
(Click here for rotating model)
Type	Archimedean solid
Elements	F=32, E=90, V=60 (χ=2)
Faces by sides	12{5}+20{6}
Schläfli symbol	t{3,5}
Wythoff symbol	2 5 | 3
Coxeter-Dynkin
Symmetry	Ih
References	U25, C27, W9
Properties	Semiregular convex
Colored faces	5.6.6 (Vertex figure)
Pentakis dodecahedron (dual polyhedron)	Net

The truncated icosahedron is an Archimedean solid. It comprises 12 regular pentagonal faces, 20 regular hexagonal faces, 60 vertices and 90 edges.

Contents 1 Construction 2 Canonical coordinates 3 Geometric relations 4 Applications 5 Truncated icosahedra in the arts 6 See also 7 References 8 External links

This polyhedron can be constructed from an icosahedron with the 12 vertices truncated (cut off) such that one third of each edge is cut off at each of both ends. This creates 12 new pentagon faces, and leaves the original 20 triangle faces as regular hexagons. Thus the length of the edges is one third of that of the original edges.

Icosahedron

Canonical coordinates for the vertices of a truncated icosahedron centered at the origin are the orthogonal rectangles (0,±1,±3φ), (±1,±3φ,0), (±3φ,0,±1) and the orthogonal cuboids (±2,±(1+2φ),±φ), (±(1+2φ),±φ,±2), (±φ,±2,±(1+2φ)) along with the orthogonal cuboids (±1,±(2+φ),±2φ), (±(2+φ),±2φ,±1), (±2φ,±1,±(2+φ)), where φ = (1+√5)/2 is the golden mean. Using φ² = φ + 1 one verifies that all vertices are on a sphere, centered at the origin, with the radius squared equal to 9φ + 10. The edges have length 2.

The truncated icosahedron easily verifies the Euler characteristic:

32 + 60 − 90 = 2.

With unit edges, the surface area is (rounded) 21 for the pentagons and 52 for the hexagons, together 73 (see areas of regular polygons).

A football (soccer) ball is an example of a truncated icosahedron found in everyday life. The ball comprises the same pattern of regular pentagons and regular hexagons, but is more spherical due to the pressure of the air inside and the elasticity of the ball.

This shape was also the configuration of the lenses used for focusing the explosive shock waves of the detonators in both the gadget and Fat Man atomic bombs (Richard Rhodes. Dark Sun: The Making of the Hydrogen Bomb, ISBN 0-684-82414-0. Touchstone Books, 1996., p. 195).

The truncated icosahedron can also be described as a model of the Buckminsterfullerene (C₆₀) molecule. The diameter of the football and the Buckminsterfullerene molecule are 22 cm and ca. 1 nm, respectively, hence the size ratio is 200,000,000 : 1.

A truncated icosahedron with "solid edges" is a drawing by Lucas Pacioli illustrating The Divine Proportion.

• spinning truncated icosahedron
• dodecahedron
• icosahedron
• icosidodecahedron
• truncated dodecahedron
• truncated rhombic triacontahedron
• hyperbolic soccerball
• fullerene

• Williams, Robert (1979). The Geometrical Foundation of Natural Structure: A Source Book of Design. Dover Publications, Inc. ISBN 0-486-23729-X.  (Section 3-9)

• Eric W. Weisstein, Truncated icosahedron at MathWorld.
• The Uniform Polyhedra
• Virtual Reality Polyhedra The Encyclopedia of Polyhedra
• Paper Models of Polyhedra Includes a paper model(net) of a Truncated Icosahedron
• Bouncing Truncated Icosahedron Virtual Reality (needs JVM)