Monogon

Monogon
On a circle, a monogon is a tessellation with a single vertex, and one 360-degree arc edge.
Type	Regular polygon
Edges and vertices	1
Schläfli symbol	{1} or h{2}
Coxeter–Dynkin diagrams	or
Symmetry group	[ ], Cs
Dual polygon	Self-dual

In geometry a monogon is a polygon with one edge and one vertex. It has Schläfli symbol {1}. Since a monogon has only one side and only one vertex, every monogon is regular by definition.

In Euclidean geometry

In Euclidean geometry a monogon is usually considered to be an impossible object, because its endpoints must coincide, unlike any Euclidean line segment. For this reason, most authorities do not consider the monogon as a proper polygon in Euclidean geometry.

In spherical geometry

In spherical geometry, a monogon can be constructed by a vertex a great circle (equator). This forms a dihedron, {1,2}, with two hemispherical monogonal faces which share one 360° edge and one vertex. Its dual, a hosohedron, {2,1} has two antipodal vertices at the poles, one 360 degree lune face, and one edge (meridian) between the two vertices.

Dihedron, {1,2}

Hosohedron, {2,1}

See also

• Regular polygon
• Digon
• Degeneracy (mathematics)

References

• Olshevsky, George. "Monogon". Glossary for Hyperspace. Archived from the original on 4 February 2007.
• Herbert Busemann, The geometry of geodesics. New York, Academic Press, 1955
• Coxeter, H.S.M; Regular Polytopes (third edition). Dover Publications Inc. ISBN 0-486-61480-8