An Icosahedron Augmented with Twenty Great Icosahedra, together with the Dual of this Cluster-Polyhedron

icosa Augmented by great Icosas.gif

The cluster-polyhedron above was formed by augmenting a central isocahedron with twenty great icosahedra. The dual of this cluster is shown below.

icosa Augmented by great Icosas dual.gif

Both these images were created using Stella 4d, which you may try for free at http://www.software3d.com/Stella.php.

Two Views of an Icosahedron, Augmented with Great Icosahedra

If colored by face-type, based on face-position in the overall solid, this “cluster” polyhedron looks like this:

Augmented Icosa using grt icosas

There is another interesting view of this polyhedral cluster I like marginally better, though, and that is to separate the faces into color-groups in which all faces of the same color are either coplanar, or parallel. It looks like this.

Augmented Icosa using grt icosas parallel faces colored together

Both versions were created by augmenting each face of a Platonic icosahedron with a great icosahedron, one of the four Kepler-Poinsot solids. I did this using Stella 4d: Polyhedron Navigator, available here.

A Cluster of Twenty Great Icosahedra, Excavated from the Faces of a Central Icosahedron, Along with Its Dual

Augmented Icosa its excavated with great icosas

These twenty great icosahedra were excavated from the faces of a central icosahedron, which is concealed in the figure’s center. These excavations exceed the limits of the central icosahedron, resulting in each great icosahedron protruding in a direction opposite that of the face from which it is excavated. In a certain sense, then, the figure above has negative volume.

To make this, I used software called Stella 4d: Polyhedron Navigator. It can be researched, bought, or tried for free here.

Also, here is the dual of the polyhedral cluster above, made with the same program.

Augmented Icosa its excavated with great icosas the dual

A Great Icosahedron, Augmented with Twenty Icosahedra

Augmented Great Icosa augmented with icosas

The polyhedral clusters above and below use different coloring-schemes, but are otherwise identical. Invisible, in the center, is a great icosahedron. Each of its faces has been augmented by a (Platonic) icosahedron.

Augmented Great Icosa augmented with icosas colored by face typeBoth images were created using Stella 4d, software you can try here.

The Greatly Augmented Icosidodecahedron, and Its Dual

Augmented Icosidodeca

If a central polyhedron’s pentagonal and triangular faces are augmented by great dodecahedra and great icosahedra, I refer to it as a “greatly augmented” polyhedron. Here, this has been done with an icosidodecahedron. The same figure appears below, but in “rainbow color” mode.

Augmented Icosidodeca colored rainbow

In the next image, “color by face type,” based on symmetry, was used.

Augmented Icosidodeca colored by face type

The next image shows the dual of this polyhedral cluster, with face color chosen on the basis of number of sides.

Augmented Icosidodeca colored by whether sides have 5 or 16 sides

Here is another version of the dual, this one in “rainbow color” mode.

Augmented Icosidodeca colored rainbow DUAL

Finally, this image of the dual is colored based on face type.

Augmented Icosidodeca colored by face type DUAL

These six images were made with Stella 4d, which may be found here.

The Greatly Augmented Rhombicosidodecahedron

Greatly Augmented Rhombicosidodeca

I call this variant on the rhombicosidocahedron “greatly augmented” because it was formed by augmenting each pentagonal face of a central rhombicosidodecahedron with great dodecahedra, while each triangular face is augmented with great icosahedra. It was made using Stella 4d, which may be found here.

An Octahedron, Augmented with Eight Great Icosahedra, and the Dual of this Augmented Polyhedral Cluster

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An Octahedron, Augmented with Eight Great Icosahedra, and the Dual of this Augmented Polyhedral Cluster

I made these using Stella 4d, which you can try at http://www.software3d.com/Stella.php. Here is its dual, also:

GrIcosadual-Augmented Octa

 

 

A Variant of the Great Icosahedron

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Faceted Dual

The great icosahedron has 20 faces which are interpenetrating equilateral triangles, most of which are hidden in the interior of that polyhedron. The non-hidden, and therefore visible, parts are called “facelets” — and there are 180 of them: 120 scalene, and 60 isosceles.

In this variant of the great icosahedron, the sixty isosceles facelets are simply missing, which changes the shape of the remaining 120, still-scalene facelets. The color scheme is one which gives each facelet a different color — except for coplanar or parallel facelets, which are the same color, making them easier to spot.

Software credit: see http://www.software3d.com/stella.php — with a free trial download available there.

My Polyhedral Nemesis: The Great Icosahedron

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My Polyhedral Nemesis:  The Great Icosahedron

I used Stella 4d, a program you can find at http://www.software3d.com/stella.php, to make the rotating .gif file you see here. You can many such rotating pictures of other polyhedra elsewhere on this blog.

Older versions of this program would only create still images. In those days, I would also make actual physical models out of paper (usually posterboard or card stock). However, I’ve stopped doing that, now that I can make these rotating pictures.

There is one polyhedron for which I never could construct a physical model, although I tried on three separate occasions. It’s this one, the great icosahedron, discovered, to the best of my knowledge, by Johannes Kepler. Although it only has twenty faces (equilateral triangles), they interpenetrate — and each triangle has nine regions visible (called “facelets”), with the rest of each face hidden inside the polyhedron.

To create a physical model, 180 of these facelets must be individually cut out, and then glued or taped together, and there’s very little margin for error. On my three construction-attempts, I did make mistakes — but did not discover them until I had already built much more of the model. When making paper models, if errors are made, there is a certain point beyond which repair is impossible, or nearly so.

Although I never succeeded in making a physical model of the great icosahedron myself, and likely never will, I did once have a team of three students in a geometry class successfully build one. One of the students kept the model, and all three received “A” grades.