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![]() Involutional symmetry Cs, (*) [ ] = ![]() | ![]() Cyclic symmetry Cnv, (*nn) [n] = ![]() ![]() ![]() | ![]() Dihedral symmetry Dnh, (*n22) [n,2] = ![]() ![]() ![]() ![]() ![]() | |
Polyhedral group, [n,3], (*n32) | |||
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![]() Tetrahedral symmetry Td, (*332) [3,3] = ![]() ![]() ![]() ![]() ![]() | ![]() Octahedral symmetry Oh, (*432) [4,3] = ![]() ![]() ![]() ![]() ![]() | ![]() Icosahedral symmetry Ih, (*532) [5,3] = ![]() ![]() ![]() ![]() ![]() |
A regularoctahedron has 24 rotational (or orientation-preserving) symmetries, and 48 symmetries altogether. These include transformations that combine a reflection and a rotation. Acube has the same set of symmetries, since it is the polyhedron that isdual to an octahedron.
The group of orientation-preserving symmetries is S4, thesymmetric group or the group of permutations of four objects, since there is exactly one such symmetry for each permutation of the four diagonals of the cube.
Chiral andfull (orachiral)octahedral symmetry are thediscrete point symmetries (or equivalently,symmetries on the sphere) with the largestsymmetry groups compatible withtranslational symmetry. They are among thecrystallographic point groups of thecubic crystal system.
Elements of O | Inversions of elements of O | ||
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identity | 0 | inversion | 0′ |
3 × rotation by 180° about a 4-fold axis | 7,16,23 | 3 × reflection in a plane perpendicular to a 4-fold axis | 7′,16′,23′ |
8 × rotation by 120° about a 3-fold axis | 3, 4, 8, 11, 12, 15, 19, 20 | 8 × rotoreflection by 60° | 3′, 4′, 8′, 11′, 12′, 15′, 19′, 20′ |
6 × rotation by 180° about a 2-fold axis | 1′, 2′, 5′, 6′, 14′, 21′ | 6 × reflection in a plane perpendicular to a 2-fold axis | 1, 2, 5, 6, 14, 21 |
6 × rotation by 90° about a 4-fold axis | 9′, 10′, 13′, 17′, 18′, 22′ | 6 × rotoreflection by 90° | 9, 10, 13, 17, 18, 22 |
Examples | ||||
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A complete list can be found inthe Wikiversity article. |
As thehyperoctahedral group of dimension 3 the full octahedral group is thewreath product, and a natural way to identify its elements is as pairs(m,n) with and.
But as it is also thedirect productS4 × S2, one can simply identify the elements of tetrahedral subgroupTd as and their inversions as.
So e.g. the identity(0, 0) is represented as 0 and the inversion(7, 0) as 0′.
(3, 1) is represented as 6 and(4, 1) as 6′.
Arotoreflection is a combination of rotation and reflection.
Illustration of rotoreflections | ||||
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Gyration axes | ||
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C4![]() | C3 > ![]() | C2![]() |
3 | 4 | 6 |
O,432, or [4,3]+ of order 24, ischiral octahedral symmetry orrotational octahedral symmetry . This group is like chiraltetrahedral symmetry T, but the C2 axes are now C4 axes, and additionally there are 6 C2 axes, through the midpoints of the edges of the cube. Td and O are isomorphic as abstract groups: they both correspond to S4, thesymmetric group on 4 objects. Td is the union of T and the set obtained by combining each element of O \ T with inversion. O is the rotation group of thecube and the regularoctahedron.
Orthogonal projection | Stereographic projection | ||
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2-fold | 4-fold | 3-fold | 2-fold |
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Oh,*432, [4,3], orm3m of order 48 –achiral octahedral symmetry orfull octahedral symmetry. This group has the same rotation axes as O, but with mirror planes, comprising both the mirror planes of Td and Th. This group is isomorphic to S4.C2, and is the full symmetry group of thecube andoctahedron. It is thehyperoctahedral group forn = 3. See alsothe isometries of the cube.
With the 4-fold axes as coordinate axes, a fundamental domain ofOh is given by 0 ≤x ≤y ≤z. An object with this symmetry is characterized by the part of the object in the fundamental domain, for example thecube is given byz = 1, and theoctahedron byx +y +z = 1 (or the corresponding inequalities, to get the solid instead of the surface).ax +by +cz = 1 gives a polyhedron with 48 faces, e.g. the disdyakis dodecahedron.
Faces are 8-by-8 combined to larger faces fora =b = 0 (cube) and 6-by-6 fora =b =c (octahedron).
The 9 mirror lines of full octahedral symmetry can be divided into two subgroups of 3 and 6 (drawn in purple and red), representing in two orthogonal subsymmetries:D2h, andTd. D2h symmetry can be doubled to D4h by restoring 2 mirrors from one of three orientations.
Octahedral symmetry and reflective subgroups | ||||||||||||||||||||||||||||||||
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Take the set of all 3×3permutation matrices and assign a + or − sign to each of the three 1s. There are permutations and sign combinations for a total of 48 matrices, giving the full octahedral group. 24 of these matrices have adeterminant of +1; these are the rotation matrices of the chiral octahedral group. The other 24 matrices have a determinant of −1 and correspond to a reflection or inversion.
Three reflectional generator matrices are needed for octahedral symmetry, which represent the three mirrors of aCoxeter–Dynkin diagram. The product of the reflections produce 3 rotational generators.
Reflections | Rotations | Rotoreflection | |||||
---|---|---|---|---|---|---|---|
Generators | R0 | R1 | R2 | R0R1 | R1R2 | R0R2 | R0R1R2 |
Group | ![]() | ![]() | ![]() | ![]() ![]() ![]() | ![]() ![]() ![]() | ![]() ![]() ![]() | ![]() ![]() ![]() ![]() ![]() |
Order | 2 | 2 | 2 | 4 | 3 | 2 | 6 |
Matrix |
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Schoenflies notation | Coxeter | Orb. | H-M | Structure | Cyc. | Order | Index | |
---|---|---|---|---|---|---|---|---|
Oh | [4,3] | ![]() ![]() ![]() ![]() ![]() | *432 | m3m | S4×S2 | 48 | 1 | |
Td | [3,3] | ![]() ![]() ![]() ![]() ![]() | *332 | 43m | S4 | ![]() | 24 | 2 |
D4h | [2,4] | ![]() ![]() ![]() ![]() ![]() | *224 | 4/mmm | D2×D8 | ![]() | 16 | 3 |
D2h | [2,2] | ![]() ![]() ![]() ![]() ![]() | *222 | mmm | D3 2 = D2×D4 | ![]() | 8 | 6 |
C4v | [4] | ![]() ![]() ![]() | *44 | 4mm | D8 | ![]() | 8 | 6 |
C3v | [3] | ![]() ![]() ![]() | *33 | 3m | D6 = S3 | ![]() | 6 | 8 |
C2v | [2] | ![]() ![]() ![]() | *22 | mm2 | D2 2 = D4 | ![]() | 4 | 12 |
Cs = C1v | [ ] | ![]() | * | 2 or m | D2 | ![]() | 2 | 24 |
Th | [3+,4] | ![]() ![]() ![]() ![]() ![]() | 3*2 | m3 | A4×S2 | ![]() | 24 | 2 |
C4h | [4+,2] | ![]() ![]() ![]() ![]() ![]() | 4* | 4/m | Z4×D2 | ![]() | 8 | 6 |
D3d | [2+,6] | ![]() ![]() ![]() ![]() ![]() | 2*3 | 3m | D12 = Z2×D6 | ![]() | 12 | 4 |
D2d | [2+,4] | ![]() ![]() ![]() ![]() ![]() | 2*2 | 42m | D8 | ![]() | 8 | 6 |
C2h = D1d | [2+,2] | ![]() ![]() ![]() ![]() ![]() | 2* | 2/m | Z2×D2 | ![]() | 4 | 12 |
S6 | [2+,6+] | ![]() ![]() ![]() ![]() ![]() | 3× | 3 | Z6 = Z2×Z3 | ![]() | 6 | 8 |
S4 | [2+,4+] | ![]() ![]() ![]() ![]() ![]() | 2× | 4 | Z4 | ![]() | 4 | 12 |
S2 | [2+,2+] | ![]() ![]() ![]() ![]() ![]() | × | 1 | S2 | ![]() | 2 | 24 |
O | [4,3]+ | ![]() ![]() ![]() ![]() ![]() | 432 | 432 | S4 | ![]() | 24 | 2 |
T | [3,3]+ | ![]() ![]() ![]() ![]() ![]() | 332 | 23 | A4 | ![]() | 12 | 4 |
D4 | [2,4]+ | ![]() ![]() ![]() ![]() ![]() | 224 | 422 | D8 | ![]() | 8 | 6 |
D3 | [2,3]+ | ![]() ![]() ![]() ![]() ![]() | 223 | 322 | D6 = S3 | ![]() | 6 | 8 |
D2 | [2,2]+ | ![]() ![]() ![]() ![]() ![]() | 222 | 222 | D4 = Z2 2 | ![]() | 4 | 12 |
C4 | [4]+ | ![]() ![]() ![]() | 44 | 4 | Z4 | ![]() | 4 | 12 |
C3 | [3]+ | ![]() ![]() ![]() | 33 | 3 | Z3 = A3 | ![]() | 3 | 16 |
C2 | [2]+ | ![]() ![]() ![]() | 22 | 2 | Z2 | ![]() | 2 | 24 |
C1 | [ ]+ | ![]() | 11 | 1 | Z1 | ![]() | 1 | 48 |
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Octahedral subgroups inCoxeter notation[1] |
The cube has 48 isometries (symmetry elements), forming thesymmetry group Oh, isomorphic toS4 × Z2. They can be categorized as follows:
An isometry of the cube can be identified in various ways:
For cubes with colors or markings (likedice have), the symmetry group is a subgroup of Oh.
Examples:
For some larger subgroups a cube with that group as symmetry group is not possible with just coloring whole faces. One has to draw some pattern on the faces.
Examples:
The full symmetry of the cube, Oh, [4,3], (*432), is preservedif and only if all faces have the same pattern such that the full symmetry of thesquare is preserved, with for the square a symmetry group,Dih4, [4], of order 8.
The full symmetry of the cube under proper rotations, O, [4,3]+, (432), is preserved if and only if all faces have the same pattern with4-fold rotational symmetry, Z4, [4]+.
InRiemann surface theory, theBolza surface, sometimes called the Bolza curve, is obtained as the ramified double cover of the Riemann sphere, with ramification locus at the set of vertices of the regular inscribed octahedron. Its automorphism group includes the hyperelliptic involution which flips the two sheets of the cover. The quotient by the order 2 subgroup generated by the hyperelliptic involution yields precisely the group of symmetries of the octahedron. Among the many remarkable properties of the Bolza surface is the fact that it maximizes thesystole among all genus 2 hyperbolic surfaces.
Class | Name | Picture | Faces | Edges | Vertices | Dual name | Picture |
---|---|---|---|---|---|---|---|
Archimedean solid (Catalan solid) | snub cube | ![]() | 38 | 60 | 24 | pentagonal icositetrahedron | ![]() |
Class | Name | Picture | Faces | Edges | Vertices | Dual name | Picture |
---|---|---|---|---|---|---|---|
Platonic solid | Cube | ![]() | 6 | 12 | 8 | Octahedron | ![]() |
Archimedean solid (dualCatalan solid) | Cuboctahedron | ![]() | 14 | 24 | 12 | Rhombic dodecahedron | ![]() |
Truncated cube | ![]() | 14 | 36 | 24 | Triakis octahedron | ![]() | |
Truncated octahedron | ![]() | 14 | 36 | 24 | Tetrakis hexahedron | ![]() | |
Rhombicuboctahedron | ![]() | 26 | 48 | 24 | Deltoidal icositetrahedron | ![]() | |
Truncated cuboctahedron | ![]() | 26 | 72 | 48 | Disdyakis dodecahedron | ![]() | |
Regular compound polyhedron | Stellated octahedron | ![]() | 8 | 12 | 8 | Self-dual | |
Cube and octahedron | ![]() | 14 | 24 | 14 | Self-dual |