Pentagramma mirificum

Pentagramma mirificum is a star polygon on a sphere, composed of five great circle arcs, all of whose internal angles are right angles. This shape was described by John Napier in his 1614 book Mirifici Logarithmorum Canonis Descriptio along with rules that link the values of trigonometric functions of five parts of a right spherical triangle. The properties of pentagramma mirificum were studied, among others, by Carl Friedrich Gauss.

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