Anticrepuscular rays

Anticrepuscular rays, or antisolar rays,[1] are meteorological optical phenomena similar to crepuscular rays, but appear opposite of the Sun in the sky. Anticrepuscular rays are essentially parallel, but appear to converge toward the antisolar point, the vanishing point, due to a visual illusion from linear perspective.[2][3]

Anticrepuscular Rays on Eastern Colorado Horizon at Dusk
Anticrepuscular rays appear opposite of the setting Sun off the Gulf Coast of the United States, as seen from Florida.
These anticrepuscular rays appear to converge at the antisolar point, as viewed from an aircraft above the clouded ocean.
Whole-sky rays.
Anticrepuscular rays appear opposite of a sunrise and perpendicular to a rainbow on the Gulf Coast of Mississippi.

Anticrepuscular rays are most frequently visible around sunrise or sunset. This is because the atmospheric light scattering that makes them visible (backscattering) is larger for low angles to the horizon than most other angles. Anticrepuscular rays are dimmer than crepuscular rays because backscattering is less than forward scattering.

Anticrepuscular rays can be continuous with crepuscular rays, curving across the whole sky in great circles.[4]

Mountain shadow

A common example of a single anticrepuscular ray is provided by the shadow of a mountain at sunset, when viewed from the summit. It appears to be triangular, whatever the shape of the mountain, with the apex at the antisolar point.[4]

Wagon-wheel spokes

Anticrepuscular rays are sometimes seen enclosed by a rainbow. In this case they can be called wagon-wheel spokes.[4]

References
  1. Cowley, Les, "Anti-solar (anti-crepuscular) rays", Atmospheric Optics, retrieved March 19, 2015
  2. John A. Day (2005), The Book of Clouds, Sterling Publishing Company, Inc., pp. 124–127, ISBN 978-1-4027-2813-6
  3. Cowley, Les, "Antisolar rays", Atmospheric Optics, retrieved March 19, 2015
  4. Lynch, D. K., & Livingston, W. (1995). Color and light in nature. Cambridge: Cambridge University Press.


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