The second time I’ve seen anticrepuscular rays this year, but this lot was a
lot more spectacular than the last.
Anticrepuscular rays are similar to crepuscular rays, but seen opposite the sun in the sky. Sunlight travels in straight lines, but the projections of these lines on Earth’s spherical atmosphere are great circles. Hence, straight-line crepuscular rays from a setting (or rising) sun can appear to re-converge at the antisolar point. Anticrepuscular rays are most frequently visible near sunrise or sunset. Crepuscular rays are usually much brighter than anticrepuscular rays. This is because for crepuscular rays, seen on the same side of the sky as the sun, the atmospheric light scattering and making them visible is taking place at small angles (see Mie theory).
Although anticrepuscular rays appear to converge onto a point opposite the sun, the convergence is actually an illusion. The rays are in fact parallel, and the apparent convergence is to the vanishing point at infinity.