Fissal enneagram

The fissal enneagram, or fen, is a polygon compound composed of 3 triangles. As such it has 9 edges and 9 vertices.

It is the second stellation of the enneagon.

Its quotient prismatic equivalent is the 9-3 step prism, which is four-dimensional.

Vertex coordinates
Coordinates for the vertices of a fissal enneagram of edge length 1 centered at the origin are given by:
 * $$\left(\frac{\sqrt3}{3},\,0\right),$$
 * $$\left(\frac{\sqrt3\cos\frac{2\pi}{9}}{3},\,±\frac{\sqrt3\sin\frac{2\pi}{9}}{3}\right),$$
 * $$\left(\frac{\sqrt3\cos\frac{4\pi}{9}}{3},\,±\frac{\sqrt3\sin\frac{4\pi}{9}}{3}\right),$$
 * $$\left(-\frac{\sqrt3}{6},\,±\frac12\right),$$
 * $$\left(\frac{\sqrt3\cos\frac{8\pi}{9}}{3},\,±\frac{\sqrt3\sin\frac{8\pi}{9}}{3}\right).$$