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A three-sided closed figure on the surface of a sphere that is bounded by the intersecting minor arcs of three great circles. Three distinct great circles can form eight triangles. Only the one formed by the three minor arcs is referred to as the spherical triangle.
A spherical triangle is called
- a right spherical triangle when it has at least one right angle;
- a birectangular spherical triangle when it has two right angles;
- a trirectangular spherical triangle when has three right angles.
A spherical triangle is called a quadrantal spherical triangle when one of its sides subtends an angle of 90° at the center of the sphere.
