Solid Angles on Spheres
1. Introduction In plane geometry, the idea of an “angle” has long been built into our intuition. The image of two rays meeting at a point sparks a vague notion of how “far apart” the two rays are: this notion is made rigorous with the definition of a , the angle required to intercept a circular arc with equal length and radius. But what happens when we leave our sheet of paper and enter the real world? How can we…