|Bowers style acronym||En|
|Coxeter diagram||x9o ()|
|Vertex figure||Dyad, length|
|Measures (edge length 1)|
|Number of external pieces||9|
|Level of complexity||1|
|Conjugates||Enneagram, great enneagram|
|Abstract & topological properties|
|Symmetry||I2(9), order 18|
The enneagon sometimes referred to as a nonagon, is a polygon with 9 sides. A regular enneagon has equal sides and equal angles.
The combining prefix in BSAs is e-, as in edip.
Like regular heptagons, regular enneagons are rarely found in higher polytopes that are objects of study, as they do not occur any non-prismatic uniform polyhedra or Johnson solids. A notable exception is the pairwise augmented cupolas, which are acrohedra. Enneagons also appear in some near-miss Johnson solids, such as the sesquitruncated octahedron.
Naming[edit | edit source]
The name enneagon is derived from the Ancient Greek ἐννέα (9) and γωνία (angle), referring to the number of vertices.
Other names include:
- En, Bowers style acronym, short for "enneagon".
Vertex coordinates[edit | edit source]
Coordinates for an enneagon of edge length , centered at the origin, are:
Variations[edit | edit source]
Besides the regular enneagon, other enneagons with triangular, mirror, or no symmetry exist. A few higher polytopes, such as certain swirlchora, have trigon-symmetric enneagons as faces.
Stellations[edit | edit source]
- 1st stellation: Enneagram
- 2nd stellation: Fissal enneagram (compound of three triangles)
- 3rd stellation: Great enneagram
External links[edit | edit source]
- Bowers, Jonathan. "Regular Polygons and Other Two Dimensional Shapes".
- Wikipedia Contributors. "Nonagon".