The Info List - Kepler-Poinsot Polyhedra

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In geometry, a Kepler–Poinsot polyhedron
Kepler–Poinsot polyhedron
is any of four regular star polyhedra.[1] They may be obtained by stellating the regular convex dodecahedron and icosahedron, and differ from these in having regular pentagrammic faces or vertex figures.


1 Characteristics

1.1 Non-convexity 1.2 Euler characteristic
Euler characteristic
χ 1.3 Duality 1.4 Summary

2 Relationships among the regular polyhedra 3 History 4 Regular star polyhedra in art and culture 5 See also 6 References 7 External links

Characteristics[edit] Non-convexity[edit] These figures have pentagrams (star pentagons) as faces or vertex figures. The small and great stellated dodecahedron have nonconvex regular pentagram faces. The great dodecahedron and great icosahedron have convex polygonal faces, but pentagrammic vertex figures. In all cases, two faces can intersect along a line that is not an edge of either face, so that part of each face passes through the interior of the figure. Such lines of intersection are not part of the polyhedral structure and are sometimes called false edges. Likewise where three such lines intersect at a point that is not a corner of any face, these points are false vertices. The images below show golden balls at the true vertices, and silver rods along the true edges. For example, the small stellated dodecahedron has 12 pentagram faces with the central pentagonal part hidden inside the solid. The visible parts of each face comprise five isosceles triangles which touch at five points around the pentagon. We could treat these triangles as 60 separate faces to obtain a new, irregular polyhedron which looks outwardly identical. Each edge would now be divided into three shorter edges (of two different kinds), and the 20 false vertices would become true ones, so that we have a total of 32 vertices (again of two kinds). The hidden inner pentagons are no longer part of the polyhedral surface, and can disappear. Now the Euler's formula holds: 60 − 90 + 32 = 2. However this polyhedron is no longer the one described by the Schläfli symbol
Schläfli symbol
5/2, 5 , and so can not be a Kepler–Poinsot solid even though it still looks like one from outside. Euler characteristic
Euler characteristic
χ[edit] A Kepler–Poinsot polyhedron
Kepler–Poinsot polyhedron
covers its circumscribed sphere more than once, with the centers of faces acting as winding points in the figures which have pentagrammic faces, and the vertices in the others. Because of this, they are not necessarily topologically equivalent to the sphere as Platonic solids are, and in particular the Euler relation

χ = V − E + F = 2  

displaystyle chi =V-E+F=2

does not always hold. Schläfli held that all polyhedra must have χ = 2, and he rejected the small stellated dodecahedron and great dodecahedron as proper polyhedra. This view was never widely held. A modified form of Euler's formula, using density (D) of the vertex figures (



displaystyle d_ v

) and faces (



displaystyle d_ f

) was given by Arthur Cayley, and holds both for convex polyhedra (where the correction factors are all 1), and the Kepler–Poinsot polyhedra:



V − E +



F = 2 D .

displaystyle d_ v V-E+d_ f F=2D.

Duality[edit] The Kepler–Poinsot polyhedra exist in dual pairs:

Small stellated dodecahedron
Small stellated dodecahedron
and great dodecahedron and Great stellated dodecahedron
Great stellated dodecahedron
and great icosahedron.


Name Picture Spherical tiling Stellation diagram Schläfli p,q and Coxeter-Dynkin Faces p Edges Vertices q Vertex figure (config.) χ Density Symmetry Dual

Small stellated dodecahedron


12 5/2 30 12 5

(5/2)5 −6 3 Ih Great dodecahedron

Great stellated dodecahedron


12 5/2 30 20 3

(5/2)3 2 7 Ih Great icosahedron

Great dodecahedron


12 5 30 12 5/2

(55)/2 −6 3 Ih Small stellated dodecahedron

Great icosahedron


20 3 30 12 5/2

(35)/2 2 7 Ih Great stellated dodecahedron

Relationships among the regular polyhedra[edit]

These share the same vertex arrangements: These share the same vertex and edge arrangements:

The icosahedron, small stellated dodecahedron, great icosahedron, and great dodecahedron.

The small stellated dodecahedron and great icosahedron.

The dodecahedron and great stellated dodecahedron.

The icosahedron and great dodecahedron.

The small stellated dodecahedron and great icosahedron share the same vertices and edges. The icosahedron and great dodecahedron also share the same vertices and edges. The three dodecahedra are all stellations of the regular convex dodecahedron, and the great icosahedron is a stellation of the regular convex icosahedron. The small stellated dodecahedron and the great icosahedron are facettings of the convex dodecahedron, while the two great dodecahedra are facettings of the regular convex icosahedron. If the intersections are treated as new edges and vertices, the figures obtained will not be regular, but they can still be considered stellations. (See also List of Wenninger polyhedron models) History[edit]

Floor mosaic in St Mark's Basilica, Venice
sometimes attributed to Paolo Uccello

Most, if not all, of the Kepler-Poinsot polyhedra were known of in some form or other before Kepler. A small stellated dodecahedron appears in a marble tarsia (inlay panel) on the floor of St. Mark's Basilica, Venice, Italy. It dates from the 15th century and is sometimes attributed to Paolo Uccello. In his Perspectiva corporum regularium (Perspectives of the regular solids), a book of woodcuts published in the 16th century, Wenzel Jamnitzer
Wenzel Jamnitzer
depicts the great dodecahedron and the great stellated dodecahedron.[2] It is clear from the general arrangement of the book that he regarded only the five Platonic solids as regular. The small and great stellated dodecahedra, sometimes called the Kepler polyhedra, were first recognized as regular by Johannes Kepler
Johannes Kepler
in 1619. He obtained them by stellating the regular convex dodecahedron, for the first time treating it as a surface rather than a solid. He noticed that by extending the edges or faces of the convex dodecahedron until they met again, he could obtain star pentagons. Further, he recognized that these star pentagons are also regular. In this way he constructed the two stellated dodecahedra. Each has the central convex region of each face "hidden" within the interior, with only the triangular arms visible. Kepler's final step was to recognize that these polyhedra fit the definition of regularity, even though they were not convex, as the traditional Platonic solids were. In 1809, Louis Poinsot
Louis Poinsot
rediscovered Kepler's figures, by assembling star pentagons around each vertex. He also assembled convex polygons around star vertices to discover two more regular stars, the great icosahedron and great dodecahedron. Some people call these two the Poinsot polyhedra. Poinsot did not know if he had discovered all the regular star polyhedra. Three years later, Augustin Cauchy
Augustin Cauchy
proved the list complete by stellating the Platonic solids, and almost half a century after that, in 1858, Bertrand provided a more elegant proof by faceting them. The following year, Arthur Cayley
Arthur Cayley
gave the Kepler–Poinsot polyhedra the names by which they are generally known today.

Conway's operational terminology gives a hexagonal diagram of relations between the 4 regular star polyhedra and 2 convex forms.[3] Stellation
changes pentagonal faces into pentagrams. Greatening maintains the face type, shifting them and resizing them into parallel planes.

A hundred years later, John Conway developed a systematic terminology for stellations in up to four dimensions. Within this scheme, he suggested slightly modified names for one of the regular star polyhedra, dropping the small adjective. Conway's names have seen some use but have not been widely adopted.

Cayley's name Conway's name and (abbreviation)

small stellated dodecahedron stellated dodecahedron (sD)

great dodecahedron (gD)

great stellated dodecahedron (gsD)

great icosahedron (gI)

Regular star polyhedra in art and culture[edit]

Alexander's Star

Regular star polyhedra first appear in Renaissance art. A small stellated dodecahedron is depicted in a marble tarsia on the floor of St. Mark's Basilica, Venice, Italy, dating from ca. 1430 and sometimes attributed to Paulo Ucello. Wenzel Jamnitzer
Wenzel Jamnitzer
published his book of woodcuts Perspectiva Corporum Regularium in 1568. He depicts the great dodecahedron and the great stellated dodecahedron - this second is slightly distorted, probably through errors in method rather than ignorance of the form. In the 20th Century, Artist M. C. Escher's interest in geometric forms often led to works based on or including regular solids; Gravitation is based on a small stellated dodecahedron. A dissection of the great dodecahedron was used for the 1980s puzzle Alexander's Star. Norwegian artist Vebjørn Sands sculpture The Kepler Star is displayed near Oslo Airport, Gardermoen. The star spans 14 meters, and consists of an icosahedron and a dodecahedron inside a great stellated dodecahedron. See also[edit] Media related to Kepler-Poinsot solids at Wikimedia Commons

Regular polytope Regular polyhedron List of regular polytopes Uniform polyhedron Uniform star polyhedron Polyhedral compound Regular star 4-polytope
Regular star 4-polytope
– the ten regular star 4-polytopes, 4-dimensional analogues of the Kepler–Poinsot polyhedra


^ Coxeter, Star polytopes and the Schläfli function f(α,β,γ) p. 121 1. The Kepler–Poinsot polyhedra ^ Perspectiva corporum regularium ^ The Symmetries of Things, p.405 Figure 26.1 Relationships among the three-dimensional star-polytopes

J. Bertrand, Note sur la théorie des polyèdres réguliers, Comptes rendus des séances de l'Académie des Sciences, 46 (1858), pp. 79–82, 117. Augustin-Louis Cauchy, Recherches sur les polyèdres. J. de l'École Polytechnique 9, 68-86, 1813. Arthur Cayley, On Poinsot's Four New Regular Solids. Phil. Mag. 17, pp. 123–127 and 209, 1859. John H. Conway, Heidi Burgiel, Chaim Goodman-Strauss, The Symmetry of Things 2008, ISBN 978-1-56881-220-5 (Chapter 24, Regular Star-polytopes, pp. 404–408) Kaleidoscopes: Selected Writings of H. S. M. Coxeter, edited by F. Arthur Sherk, Peter McMullen, Anthony C. Thompson, Asia Ivic Weiss, Wiley-Interscience Publication, 1995, ISBN 978-0-471-01003-6 [1]

(Paper 1) H.S.M. Coxeter, The Nine Regular Solids [Proc. Can. Math. Congress 1 (1947), 252–264, MR 8, 482] (Paper 10) H.S.M. Coxeter, Star Polytopes and the Schlafli Function f(α,β,γ) [Elemente der Mathematik 44 (2) (1989) 25–36]

P. Cromwell, Polyhedra, Cabridgre University Press, Hbk. 1997, Ppk. 1999. Theoni Pappas, (The Kepler–Poinsot Solids) The Joy of Mathematics. San Carlos, CA: Wide World Publ./Tetra, p. 113, 1989. Louis Poinsot, Memoire sur les polygones et polyèdres. J. de l'École Polytechnique 9, pp. 16–48, 1810. Lakatos, Imre; Proofs and Refutations, Cambridge University Press (1976) - discussion of proof of Euler characteristic Wenninger, Magnus (1983). Dual Models. Cambridge University Press. ISBN 0-521-54325-8. , pp. 39–41. John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 (Chapter 26. pp. 404: Regular star-polytopes Dimension 3) Anthony Pugh (1976). Polyhedra: A Visual Approach. California: University of California Press Berkeley. ISBN 0-520-03056-7.  Chapter 8: Kepler Poisot polyhedra

External links[edit]

Weisstein, Eric W. "Kepler–Poinsot solid". MathWorld.  Paper models of Kepler–Poinsot polyhedra Free paper models (nets) of Kepler–Poinsot polyhedra The Uniform Polyhedra VRML models of the Kepler–Poinsot polyhedra Stellation
and facetting - a brief history Stella: Polyhedron Navigator: Software used to create many of the images on this page.

v t e

Star-polyhedra navigator

Kepler-Poinsot polyhedra (nonconvex regular polyhedra)

small stellated dodecahedron great dodecahedron great stellated dodecahedron great icosahedron

Uniform truncations of Kepler-Poinsot polyhedra

dodecadodecahedron truncated great dodecahedron rhombidodecadodecahedron truncated dodecadodecahedron snub dodecadodecahedron great icosidodecahedron truncated great icosahedron nonconvex great rhombicosidodecahedron great truncated icosidodecahedron

Nonconvex uniform hemipolyhedra

tetrahemihexahedron cubohemioctahedron octahemioctahedron small dodecahemidodecahedron small icosihemidodecahedron great dodecahemidodecahedron great icosihemidodecahedron great dodecahemicosahedron small dodecahemicosahedron

Duals of nonconvex uniform polyhedra

medial rhombic triacontahedron small stellapentakis dodecahedron medial deltoidal hexecontahedron small rhombidodecacron medial pentagonal hexecontahedron medial disdyakis triacontahedron great rhombic triacontahedron great stellapentakis dodecahedron great deltoidal hexecontahedron great disdyakis triacontahedron great pentagonal hexecontahedron

Duals of nonconvex uniform polyhedra with infinite stellations

tetrahemihexacron hexahemioctacron octahemioctacron small dodecahemidodecacron small icosihemidodecacron great dodecahemidodecacron great icosihemidodecacron great dodecahemicosacron small dodeca