Truncated icosahedron

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Truncated icosahedron
Truncatedicosahedron.jpg
(Click here for rotating model)
Type Archimedean solid
Uniform polyhedron
Elements F = 32, E = 90, V = 60 (χ = 2)
Faces by sides12{5}+20{6}
Conway notation tI
Schläfli symbols t{3,5}
t0,1{3,5}
Wythoff symbol 2 5 | 3
Coxeter diagram CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.png
Symmetry group Ih, H3, [5,3], (*532), order 120
Rotation group I, [5,3]+, (532), order 60
Dihedral angle 6-6: 138.189685°
6-5: 142.62°
References U 25, C 27, W 9
PropertiesSemiregular convex
Polyhedron truncated 20 max.png
Colored faces
Polyhedron truncated 20 vertfig.svg
5.6.6
(Vertex figure)
Polyhedron truncated 20 dual max.png
Pentakis dodecahedron
(dual polyhedron)
Polyhedron truncated 20 net compact.svg
Net

In geometry, the truncated icosahedron is an Archimedean solid, one of 13 convex isogonal nonprismatic solids whose 32 faces are two or more types of regular polygons. It is the only one of these shapes that does not contain triangles or squares. In general usage, the degree of truncation is assumed to be uniform unless specified.

Contents

It has 12 regular pentagonal faces, 20 regular hexagonal faces, 60 vertices and 90 edges.

It is the Goldberg polyhedron GPV(1,1) or {5+,3}1,1, containing pentagonal and hexagonal faces.

This geometry is associated with footballs (soccer balls) typically patterned with white hexagons and black pentagons. Geodesic domes such as those whose architecture Buckminster Fuller pioneered are often based on this structure. It also corresponds to the geometry of the fullerene C60 ("buckyball") molecule.

It is used in the cell-transitive hyperbolic space-filling tessellation, the bitruncated order-5 dodecahedral honeycomb.

Construction

Icosahedron Polyhedron 20 max.png
Icosahedron

This polyhedron can be constructed from an icosahedron by truncating, or cutting off, each of the 12 vertices at the one-third mark of each edge, creating 12 pentagonal faces and transforming the original 20 triangle faces into regular hexagons. [1] [2]

Characteristics

In geometry and graph theory, there are some standard polyhedron characteristics.

Cartesian coordinates

Cartesian coordinates for the vertices of a truncated icosahedron centered at the origin are all even permutations of:

where is the golden mean. The circumradius is and the edges have length 2. [3]

Orthogonal projections

The truncated icosahedron has five special orthogonal projections, centered, on a vertex, on two types of edges, and two types of faces: hexagonal and pentagonal. The last two correspond to the A2 and H2 Coxeter planes.

Orthogonal projections
Centered byVertexEdge
5-6
Edge
6-6
Face
Hexagon
Face
Pentagon
Solid Polyhedron truncated 20 from blue max.png Polyhedron truncated 20 from yellow max.png Polyhedron truncated 20 from red max.png
Wireframe Dodecahedron t12 v.png Dodecahedron t12 e56.png Dodecahedron t12 e66.png Icosahedron t01 A2.png Icosahedron t01 H3.png
Projective
symmetry
[2][2][2][6][10]
Dual Dual dodecahedron t01 v.png Dual dodecahedron t01 e56.png Dual dodecahedron t01 e66.png Dual dodecahedron t01 A2.png Dual dodecahedron t01 H3.png

Spherical tiling

The truncated icosahedron can also be represented as a spherical tiling, and projected onto the plane via a stereographic projection. This projection is conformal, preserving angles but not areas or lengths. Straight lines on the sphere are projected as circular arcs on the plane.

Uniform tiling 532-t12.png Truncated icosahedron stereographic projection pentagon.png
pentagon-centered
Truncated icosahedron stereographic projection hexagon.png
hexagon-centered
Orthographic projection Stereographic projections

Dimensions

Mutually orthogonal golden rectangles drawn into the original icosahedron (before cut off) Icosahedron-golden-rectangles.svg
Mutually orthogonal golden rectangles drawn into the original icosahedron (before cut off)

If the edge length of a truncated icosahedron is a, the radius of a circumscribed sphere (one that touches the truncated icosahedron at all vertices) is:

where φ is the golden ratio.

This result is easy to get by using one of the three orthogonal golden rectangles drawn into the original icosahedron (before cut off) as the starting point for our considerations. The angle between the segments joining the center and the vertices connected by shared edge (calculated on the basis of this construction) is approximately 23.281446°.

Area and volume

The area A and the volume V of the truncated icosahedron of edge length a [4] are:

With unit edges, the surface area is (rounded) 21 for the pentagons and 52 for the hexagons, together 73 (see areas of regular polygons). The truncated icosahedron easily demonstrates the Euler characteristic:

Applications

The balls used in association football and team handball are perhaps the best-known example of a spherical polyhedron analog to the truncated icosahedron, found in everyday life. [5] The ball comprises the same pattern of regular pentagons and regular hexagons, but it is more spherical due to the pressure of the air inside and the elasticity of the ball. This ball type was introduced to the World Cup in 1970 (starting in 2006, this iconic design has been superseded by alternative patterns).

Geodesic domes are typically based on triangular facetings of this geometry with example structures found across the world, popularized by Buckminster Fuller. [6]

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. [7]

The truncated icosahedron can also be described as a model of the Buckminsterfullerene (fullerene) (C60), or "buckyball", molecule – an allotrope of elemental carbon, discovered in 1985. The diameter of the football and the fullerene molecule are 22 cm and about 0.71  nm, respectively, hence the size ratio is ≈31,000,000:1.

In popular craft culture, large sparkleballs can be made using a icosahedron pattern and plastic, styrofoam or paper cups.

In the arts

Family of uniform icosahedral polyhedra
Symmetry: [5,3], (*532)[5,3]+, (532)
Uniform polyhedron-53-t0.svg Uniform polyhedron-53-t01.svg Uniform polyhedron-53-t1.svg Uniform polyhedron-53-t12.svg Uniform polyhedron-53-t2.svg Uniform polyhedron-53-t02.png Uniform polyhedron-53-t012.png Uniform polyhedron-53-s012.png
CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.pngCDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel node.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel node h.pngCDel 5.pngCDel node h.pngCDel 3.pngCDel node h.png
{5,3} t{5,3} r{5,3} t{3,5} {3,5} rr{5,3} tr{5,3} sr{5,3}
Duals to uniform polyhedra
Icosahedron.svg Triakisicosahedron.jpg Rhombictriacontahedron.svg Pentakisdodecahedron.jpg Dodecahedron.svg Deltoidalhexecontahedron.jpg Disdyakistriacontahedron.jpg Pentagonalhexecontahedronccw.jpg
V5.5.5 V3.10.10 V3.5.3.5 V5.6.6 V3.3.3.3.3 V3.4.5.4 V4.6.10 V3.3.3.3.5
*n32 symmetry mutation of truncated tilings: n.6.6
Sym.
*n42
[n,3]
Spherical Euclid. CompactParac.Noncompact hyperbolic
*232
[2,3]
*332
[3,3]
*432
[4,3]
*532
[5,3]
*632
[6,3]
*732
[7,3]
*832
[8,3]...
*32
[,3]
[12i,3][9i,3][6i,3]
Truncated
figures
Hexagonal dihedron.svg Uniform tiling 332-t12.png Uniform tiling 432-t12.png Uniform tiling 532-t12.png Uniform tiling 63-t12.svg Truncated order-7 triangular tiling.svg H2-8-3-trunc-primal.svg H2 tiling 23i-6.png H2 tiling 23j12-6.png H2 tiling 23j9-6.png H2 tiling 23j-6.png
Config. 2.6.6 3.6.6 4.6.6 5.6.6 6.6.6 7.6.6 8.6.6 .6.6 12i.6.69i.6.66i.6.6
n-kis
figures
Hexagonal Hosohedron.svg Spherical triakis tetrahedron.svg Spherical tetrakis hexahedron.svg Spherical pentakis dodecahedron.png Uniform tiling 63-t2.svg Heptakis heptagonal tiling.svg H2-8-3-kis-dual.svg H2checkers 33i.png
Config. V2.6.6 V3.6.6 V4.6.6 V5.6.6 V6.6.6 V7.6.6V8.6.6V.6.6V12i.6.6V9i.6.6V6i.6.6

These uniform star-polyhedra, and one icosahedral stellation have nonuniform truncated icosahedra convex hulls:

This polyhedron looks similar to the uniform chamfered dodecahedron which has 12 pentagons, but 30 hexagons.

Truncated icosahedral graph

Truncated icosahedral graph
Truncated icosahedral graph.png
6-fold symmetry schlegel diagram
Vertices 60
Edges 90
Automorphisms 120
Chromatic number 3
Properties Cubic, Hamiltonian, regular, zero-symmetric
Table of graphs and parameters

In the mathematical field of graph theory, a truncated icosahedral graph is the graph of vertices and edges of the truncated icosahedron, one of the Archimedean solids. It has 60 vertices and 90 edges, and is a cubic Archimedean graph. [8] [9] [10]

Orthographic projection
Icosahedron t01 H3.png
5-fold symmetry
Truncated icosahedral graph pentcenter.png
5-fold Schlegel diagram

History

Piero della Francesca's image of a truncated icosahedron from his book De quinque corporibus regularibus Piero della Francesca - Libellus de quinque corporibus regularibus - p52b (cropped).jpg
Piero della Francesca's image of a truncated icosahedron from his book De quinque corporibus regularibus

The truncated icosahedron was known to Archimedes, who classified the 13 Archimedean solids in a lost work. All we know of his work on these shapes comes from Pappus of Alexandria, who merely lists the numbers of faces for each: 12 pentagons and 20 hexagons, in the case of the truncated icosahedron. The first known image and complete description of a truncated icosahedron is from a rediscovery by Piero della Francesca, in his 15th-century book De quinque corporibus regularibus , [11] which included five of the Archimedean solids (the five truncations of the regular polyhedra). The same shape was depicted by Leonardo da Vinci, in his illustrations for Luca Pacioli's plagiarism of della Francesca's book in 1509. Although Albrecht Dürer omitted this shape from the other Archimedean solids listed in his 1525 book on polyhedra, Underweysung der Messung, a description of it was found in his posthumous papers, published in 1538. Johannes Kepler later rediscovered the complete list of the 13 Archimedean solids, including the truncated icosahedron, and included them in his 1609 book, Harmonices Mundi . [12]

See also

Notes

  1. Mednikov, Evgueni G.; Jewell, Matthew C.; Dahl, Lawrence F. (2007-09-01). "Nanosized (μ 12 -Pt)Pd 164- x Pt x (CO) 72 (PPh 3 ) 20 ( x ≈ 7) Containing Pt-Centered Four-Shell 165-Atom Pd−Pt Core with Unprecedented Intershell Bridging Carbonyl Ligands: Comparative Analysis of Icosahedral Shell-Growth Patterns with Geometrically Related Pd 145 (CO) x (PEt 3 ) 30 ( x ≈ 60) Containing Capped Three-Shell Pd 145 Core". Journal of the American Chemical Society. 129 (37): 11624. doi:10.1021/ja073945q. ISSN   0002-7863. PMID   17722929.
  2. Kotschick, Dieter (July–August 2006). "The Topology and Combinatorics of Soccer Balls". American Scientist . 94 (4): 350. doi:10.1511/2006.60.350.
  3. Weisstein, Eric W. "Icosahedral group". MathWorld .
  4. Weisstein, Eric W. "Truncated Icosahedron". mathworld.wolfram.com. Retrieved 2023-09-10.
  5. Kotschick, Dieter (2006). "The Topology and Combinatorics of Soccer Balls". American Scientist. 94 (4): 350–357. doi:10.1511/2006.60.350.
  6. Krebs, Albin (July 2, 1983). "R. Buckminster Fuller Dead; Futurist Built Geodesic Dome". The New York Times. New York, N.Y. p. 1. Retrieved 7 November 2021.
  7. Rhodes, Richard (1996). Dark Sun: The Making of the Hydrogen Bomb. Touchstone Books. pp.  195. ISBN   0-684-82414-0.
  8. Read, R. C.; Wilson, R. J. (1998). An Atlas of Graphs. Oxford University Press. p. 268.
  9. Godsil, C. and Royle, G. Algebraic Graph Theory New York: Springer-Verlag, p. 211, 2001
  10. Kostant, B. The Graph of the Truncated Icosahedron and the Last Letter of Galois. Notices Amer. Math. Soc. 42, 1995, pp. 959-968 PDF
  11. Katz, Eugene A. (2011). "Bridges between mathematics, natural sciences, architecture and art: case of fullerenes". Art, Science, and Technology: Interaction Between Three Cultures, Proceedings of the First International Conference. pp. 60–71.
  12. Field, J. V. (1997). "Rediscovering the Archimedean polyhedra: Piero della Francesca, Luca Pacioli, Leonardo da Vinci, Albrecht Dürer, Daniele Barbaro, and Johannes Kepler". Archive for History of Exact Sciences . 50 (3–4): 241–289. doi:10.1007/BF00374595. JSTOR   41134110. MR   1457069. S2CID   118516740.

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References