English: Diagram of a sphere with three great circles forming a (blue) spherical triangle. A second (orange) spherical triangle is superimposed. The orange triangle is obtained by reflecting the blue triangle across one of its sides. The diagram is animated. The orange triangle rotates about each of the vertices of the blue triangle in turn, through an angle measuring twice the corresponding angle of the blue triangle. Thus the orange triangle rotates around each vertex of the blue triangle until it is alongside the next edge. After three such rotations the orange triangle has returned to its original position and the animation repeats.