A Variant of Kepler’s Stella Octangula

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A Variant of Kepler's Stella Octangula

Johannes Kepler named the compound of two tetrahedra the “stella octangula,” thus helping make it one of the best-known polyhedral compounds today. This variant uses triakis tetrahedra in place of the Platonic tetrahedra in that compound. The triakis tetrahedron is a Catalan solid, and is dual to the truncated tetrahedron.

Software credit: see http://www.software3d.com/stella.php to try or buy Stella 4d, the software I used to create this image.

The Compound of Six Dodecahedra

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The Compound of Six Dodecahedra

Some polyhedral compounds are well-known, such as the compound of five cubes, while others are less famous. I had never heard of this compound before building one today (virtually, not as a physical model). However, a quick Google-search told me that I was not the first person to discover it.

Software credit: see http://www.software3d.com/stella.php to try or buy Stella 4d, the software I used to create this image.

The Pentagonal Hexacontahedron, and Related Polyhedra

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The Pentagonal Hexacontahedron

As the dual of the snub dodecahedron, which is chiral, this member of the Catalan Solids is also chiral — in other words, it exists in left- and right-handed versions, known an entantiomers. They are mirror-images of each other, like left and right gloves or shoes. Here’s the other one, by comparison:

Penta Hexeconta enantiomer

It is always possible to make a compound, for a chiral polyhedron, from its two enantiomers. Here’s the one made from the two mirror-image pentagonal hexacontahedra shown above:

Compound of enantiomorphic pair

Stellating this enantiomorphic-pair-compound twenty-one times produces this interesting result:

stellating

And, returning to the unstellated enantiamorphic-pair-compound, here is its convex hull:

Convex hull

This convex hull strikes me as an interesting polyhedron in its own right, so I tried stellating it several times, just to see what would happen. Here’s one result, after seventeen stellations:

Stellation17

Software credit:  I made these rotating images using Stella 4d:  Polyhedron Navigator. That program may be bought at http://www.software3d.com/Stella.php, and has a free “try it before you buy it” trial download available at that site, as well. I also used Geometer’s Sketchpad and MS-Paint to produce the flat purple-and-black image found on faces near the top of this post (and, by itself, in the previous post on this blog), but I know of nowhere to get free trial downloads of these latter two programs.

The Compound of the Rhombic Dodecahedron and Its Own Third Stellation

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The Compound of the Rhombic Dodecahedron and Its Own Third Stellation

Software credit: see http://www.software3d.com/stella.php

Compound of the Great Dodecahedron and the Sixth Stellation of the Icosahedron

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Compound of the Great Dodecahedron and a Stellated Polyhedron

The great dodecahedron here is red, and the yellow polyhedron is the sixth stellation of the icosahedron.

Software credit: http://www.software3d.com/stella.php

Compound of the Octahedron and the Tetrakis Hexahedron

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Compound of the Octahedron and the Tetrakis Hexahedron

This polyhedral compound was found by repeatedly-stellating the 38-faced polyhedron featured in the last post.

Software credit: http://www.software3d.com/stella.php

The Stella Octangula, Combined with the Cube/Octahedron Compound

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The Stella Octangula, Combined with the Cube/Octahedron Compound

Software credit: http://www.software3d.com/stella.php

Compound of Four Triangular Prisms

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Compound of Four Triangular Prisms

Software credit: see http://www.software3d.com/stella.php

Compound of the Truncated Icosahedron and Its Dual, the Pentakis Dodecahedron

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Compound of the Truncated Icosahedron and Its Dual, the Pentakis Dodecahedron

Software credit: see http://www.software3d.com/stella.php

A Twisted Version of the Stella Octangula

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A Twisted Version of the Stella Octangula

For comparison, here’s the non-twisted, traditional Stella Octangula:

Tetra

Software credit: http://www.software3d.com/stella.php