What Are Crepuscular Rays?

By Ferdinand Bada on April 2 2019 in Environment

Crepuscular rays light up portions of the Blue Ridge Mountains in North Carolina.
Crepuscular rays light up portions of the Blue Ridge Mountains in North Carolina.

Crepuscular rays are rays of the sun that seem to emerge from the general position of the sun in the sky. These rays appear when things such as heavy clouds, especially stratocumulus clouds, and big objects obscure the sun. Despite appearing to converge on one point, the seeming convergence is actually an illusion. An example of a similar illusion is the way that a long hallway or railway line appears to narrow down until the two sides come together at a distance. Another example is seen when a person is observing parallel furrows on a field. As the distance away from the furrows increases, they appear to be converging.

Definition and Meaning

By definition, the word crepuscular points to something that resembles or is related to twilight hours, which is where the rays got their name. The word “crepuscular” actually stems from the word “crepusculum,” which is Latin for twilight. Accordingly, crepuscular rays tend to appear during twilight periods, that is, dawn and dusk. At that point, they are easily observed because there is a high difference between darkness and light.

Color and Alternate Names

The rays usually take up an orange hue mainly because of the time of day that they appear. During twilight hours, the rays are forced to travel through a lot more air compared to other times during the day. Studies have shown that the amount of air during twilight hours is at least 40 times as much as during midday.

Aside from the already stated alternative names, the rays have several other names depending on the perspective. For example, in the nautical world, they are known as backstays of the sun. Other names include Buddha rays, cloud breaks, directional lighting (computer graphics), Fingers of God, God’s Eye, Jacob’s ladder, and Jesus rays.

Scattering and Perception

One key component of these rays is the shadow that occurs between the rays of light. Any number of objects or things such as clouds, windows, trees, mountains, and other things form these shadows. Humans would not be able to see these beams without the particles reflected by the light. A similar event is observed when someone observes a beam of light through lots of dust particles, which makes the light more perceivable. The eyes then perceive this light and the brain does the processing of this data to create the illusion.

Anticrepuscular Rays

Also known as antisolar rays, anticrepuscular rays are the direct opposite of crepuscular rays. While crepuscular rays appear to originate from one point in the sky, anticrepuscular rays appear to converge at a point away from the sun. In other words, they give the distinct impression that they are diverging from the sky due to an illusion similar to that of crepuscular rays. Just like the crepuscular rays, anticrepuscular rays also appear at dusk or dawn. However, they are also different in their brightness. Compared to crepuscular rays, anticrepuscular rays are considerably dimmer. While it may be difficult to see anticrepuscular rays, they can sometimes be seen together with crepuscular rays.

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