A sunbeam, in meteorological optics, is a beam of sunlight that appears to radiate from the position of the Sun.
Shining through openings in clouds or between other objects such as mountains and buildings, these beams of particle-scattered sunlight are essentially parallel shafts separated by darker shadowed volumes.
The same illusion causes the apparent convergence of parallel lines on a long straight road or hallway at a distant vanishing point.
[1] The scattering particles that make sunlight visible may be air molecules or particulates.
[7] This apparent dual convergence (at both the solar and the antisolar points) is a perspective effect analogous to the apparent dual convergence of the parallel lines of a long straight road or hallway at directly opposite points (to an observer above the ground).