The study of figures on the surface of a sphere (such as the spherical triangle and spherical polygon), as opposed to the type of geometry studied in plane geometry or solid geometry. In spherical geometry, straight lines are great circles, so any two lines meet in two points. There are also no parallel lines. The angle between two lines in spherical geometry is the angle between the planes of the corresponding great circles, and a spherical triangle is defined by its three angles. There is no concept of similar triangles in spherical geometry.

great circle | hyperbolic geometry | plane geometry | solid geometry | spherical triangle | spherical trigonometry | Thurston's geometrization conjecture