# Monthly Archives: January 2020

# A Euclidean Construction of a Regular Triacontagon

Steps of this construction:

- Use the green circles and blue lines to construct the yellow pentagon, along with its green inscribed pentagram.
- Construct the equilateral triangle shown in gray. This is needed to obtain a twelve degree angle. The triangle is needed for its sixty degree angle, because 72 – 60 = 12. (The 72 degree angle is found inside the pentagon.)
- Identify the twelve degree angle shown in bold. A twelve degree angle is needed because 360 / 30 = 12.
- Use the red circles to complete the thirty sides of the regular triacontagon, which is shown with bold black segments, inscribed inside a large, bold, red circle.

# Eyes

This collection of curves was built around a tessellation of the plane using regular hexagons. To make the second version, I inverted the colors, except for the black circles and arcs.

## A Picture of Five

### Image

# A Dozen Dodecahedra, Surrounding an Icosahedron

I made these virtual models using *Stella 4d: Polyhedron Navigator*. If you’d like to try this program for yourself — free — the website to visit is http://www.software3d.com/Stella.php.

# A Parallelogram-Expanded Snub Dodecahedron

The snub dodecahedron may be thought of as a dozen regular pentagons, surrounded and separated by a sea of triangles. In this expansion of that Archimedean solid, thirty parallelograms are added to the mix, also surrounded by triangles. In the image above, coloring is by face type — for example, the yellow triangles are those triangles which share an edge with a pentagon. Other triangles have other colors.

The image shown below is of the same polyhedron, but with a different coloring-scheme. In it, all triangles are given the same color, even when their shapes are slightly different.

This polyhedron has an interesting all-pentagon dual, which is shown below. This dual has sixty each of both the small and large pentagons, for a total of 120 faces.

I used *Stella 4d: Polyhedron Navigator* to create these polyhedra, and to make these rotating images. This program may be tried for free at http://www.software3d.com/Stella.php.

# An Embellished Icosahedron

Created using *Stella 4d*, which you can try for free at http://www.software3d.com/Stella.php.

# A Compound of Six Pentadecagonal Prisms

This chiral polyhedral compound was generated from a partial faceting of the polyhedron shown in the last post here, using *Stella 4d*‘s faceting function, plus its “try to make faces regular” operation afterwards. Making the six-prism compound in the first place was suggested by Tony Hartley, on Facebook, where I posted a link to that last post in a mathematical group for discussion. Thanks, Tony!

If you’d like to try *Stella* for yourself, the site to visit for a free trial download is http://www.software3d.com/Stella.php.

# An Unusual Polyhedron with 200 Faces

This polyhedron was made from the faceted rhombicosidodecahedron in the post immediately before this one, by stellating it a few times. Its 200 faces include twenty equilateral triangles (yellow), sixty irregular decagons (green), and two sets of sixty trapezoids each (red and blue). I made it using *Stella 4d*, which you can try for free at http://www.software3d.com/Stella.php.

# A Faceting of the Rhombicosidodecahedron

I made this faceting of the rhombicosidodecahedron using *Stella 4d: Polyhedron Navigator*. You can try this program out, for free, at http://www.software3d.com/Stella.php.