Continuous black curves are obtained from the original time delay Eq. (5), while the dashed red curves are from the polynomial approximate Eq. (22). Different panels show R = 2r_s, R = 3r_s and R = 5r_s. The dotted blue line helps distinguishing trajectories without a turning point (i.e., 0 ≤ cosα ≤ 1) from those with a turning point (i.e., π/ 2 ≤ α ≤ α_max). The lower panels show the difference between the curves from the original and approximate equations.