Editing Spherical trigonometry (section)

===Spherical polygons===
A '''spherical polygon''' is a ''[[polygon]]'' on the surface of the sphere. Its sides are [[Circular arc|arc]]s of [[great circle]]s—the spherical geometry equivalent of [[line segment]]s in [[Euclidean geometry|plane geometry]].

Such polygons may have any number of sides greater than 1. Two-sided spherical polygons—''[[spherical lune|lune]]s'', also called ''[[digon]]s'' or ''bi-angles''—are bounded by two great-circle arcs: a familiar example is the curved outward-facing surface of a segment of an orange. Three arcs serve to define a spherical triangle, the principal subject of this article. Polygons with higher numbers of sides (4-sided spherical quadrilaterals, 5-sided spherical pentagons, etc.) are defined in similar manner. Analogously to their plane counterparts, spherical polygons with more than 3 sides can always be treated as the composition of spherical triangles.

One spherical polygon with interesting properties is the [[pentagramma mirificum]], a 5-sided spherical [[star polygon]] with a right angle at every vertex.

From this point in the article, discussion will be restricted to spherical triangles, referred to simply as ''triangles''.