Anticrepuscular

Anticrepuscular rays are a visual atmospheric phenomenon in which parallel sunbeams and their shadows appear to converge toward the antisolar point—the point on the sky directly opposite the Sun. They are the counterpart of crepuscular rays, which seem to diverge from the Sun.

The effect arises from the geometry of light and perspective. In three-dimensional space the rays are nearly parallel, but as the sky is a curved dome, the lines seem to meet at the antisolar point when viewed from Earth. The light portions occur where sunlight passes through gaps in clouds or other clearings, while the darker bands align with cloud shadows cast by the same features.

Anticrepuscular rays are most noticeable when the Sun sits low on the horizon, such as near sunrise or sunset, and when there are distinct, contrasting cloud gaps opposite the Sun. They can extend across a large portion of the sky, though they are typically easiest to observe near the horizon and under favorable atmospheric conditions. The phenomenon is a result of atmospheric optics and perspective rather than a true focal point of light.

In practice, anticrepuscular rays are a rarely noticed variant of a common optical effect linked to crepuscular rays. The term is used in meteorology and observational astronomy to describe the opposite-horizon counterparts of sunlit beams and shadow bands seen during sunrise or sunset.