Octagram

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Regular octagram
Regular star polygon 8-3.svg
A regular octagram
Type Regular polygon
Edges and vertices 8
Schläfli symbol {8/3}
t{4/3}
Coxeter diagram CDel node 1.pngCDel 8.pngCDel rat.pngCDel d3.pngCDel node.png
CDel node 1.pngCDel 4.pngCDel rat.pngCDel d3.pngCDel node 1.png
Symmetry group Dihedral (D8)
Internal angle (degrees) 45°
Dual polygon self
Properties star, cyclic, equilateral, isogonal, isotoxal

In geometry, an octagram is an eight-sided star polygon.

The name octagram combine a numeral prefix, octa-, with the Greek suffix -gram. The -gram suffix derives from γραμμῆς (grammos) meaning a line.[1]

Geometry[edit]

In general, an octagram is any self-intersecting octagon (8-sided polygon).

The regular octagram is labeled by the Schläfli symbol {8/3}, which means an 8-sided star, connected by every 3rd point.

Octagram lengths.svg

Variations[edit]

These variations have a lower dihedral, Dih4, symmetry:

Regular truncation 4 1.5.svg
Narrow
Regular truncation 4 2.svg
Wide
(45 degree rotation)
Isotoxal octagram.png
Octagram-in-square.svg
Isotoxal
Star Guñelve.svg
An old Flag of Chile contained this octagonal star geometry, rotated 45 degrees, and edges removed.
Ancient mapuche flag.svg
The geometry can be adjusted so 3 edges cross at a single point, like the Auseklis symbol
Compass rose en 08p.svg
An 8-point compass rose can be seen as an octagonal star, with 4 primary points, and 4 secondary points.

The symbol Rub el Hizb is a Unicode glyph ۞  at U+06DE.

As a quasitruncated square[edit]

Deeper truncations of the square can produce isogonal (vertex-transitive) intermediate star polygon forms with equal spaced vertices and two edge lengths. A truncated square is an octagon, t{4}={8}. A quasitruncated square, inverted as {4/3}, is an octagram, t{4/3}={8/3}.[2]

The uniform star polyhedron stellated truncated hexahedron, t'{4,3}=t{4/3,3} has octagram faces constructed from the cube in this way.

Isogonal truncations of square and cube
Regular Quasiregular Isogonal Quasiregular
Regular quadrilateral.svg
{4}
Regular polygon truncation 4 1.svg
t{4}={8}
Regular polygon truncation 4 2.svg Regular polygon truncation 4 3.svg
t'{4}=t{4/3}={8/3}
Regular Uniform Isogonal Uniform
Cube truncation 0.00.png
{4,3}
Cube truncation 0.50.png
t{4,3}
Cube truncation 3.50.png Cube truncation 2.50.png
t'{4,3}=t{4/3,3}

Regular star polygon compounds[edit]

There are two octagrammic star figures (compounds) of the form {8/k}, the first constructed as two squares {8/2}=2{4}, and second as four degenerate digons, {8/4}=4{2}.

Regular star figure 2(4,1).svg
a{8}={8/2}=2{4}
Star of Lakshmi
Regular star figure 4(2,1).svg
{8/4}=4{2}

Other presentations of an octagonal star[edit]

An octagonal star can be seen as a concave hexadecagon, with internal intersecting geometry erased. It can also be dissected by radial lines.

2{4} Ashthalakshmi - Star of Laxmi.svg Squared octagonal star.png Squared octagonal star1.png Squared octagonal star2.png
{8/3} Octagram graph.png Octagonal star.png Octagonal star2.png Octagonal star3.png
Auseklis star.svg Octagonal star-b.png Octagonal star-b2.png Octagonal star-b3.png
Isotoxal octagram.png Octagonal star-c.png Octagonal star-c2.png Octagonal star-c3.png

See also[edit]

Usage
Stars generally

References[edit]

  1. ^ γραμμή, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  2. ^ The Lighter Side of Mathematics: Proceedings of the Eugène Strens Memorial Conference on Recreational Mathematics and its History, (1994), Metamorphoses of polygons, Branko Grünbaum
  • Grünbaum, B. and G.C. Shephard; Tilings and Patterns, New York: W. H. Freeman & Co., (1987), ISBN 0-7167-1193-1.
  • Grünbaum, B.; Polyhedra with Hollow Faces, Proc of NATO-ASI Conference on Polytopes ... etc. (Toronto 1993), ed T. Bisztriczky et al., Kluwer Academic (1994) pp. 43–70.
  • John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 (Chapter 26. pp. 404: Regular star-polytopes Dimension 2)

External links[edit]