This collection of articles highlights all possible trajectories of particles and light under the influence of a gravitational field of all possible strengths that may exist in our universe, including that of a black hole; and it also highlights the beautiful mathematical formulas that can express all these trajectories, according to Einstein’s theory of general relativity. For this to be possible, the authors use mathematical functions called elliptic functions that can describe orbits, including the familiar circular, elliptical, parabolic and hyperbolic orbits. Some readers can put aside...