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Crepuscular Rays and Their Formation

Nicks J Oct 08, 2020
When the sunlight is blocked partially by obstacles, such as clouds, the brilliant beams of light that emerge radiating from beyond these objects are referred to as crepuscular rays. This phenomenon can also be seen when mountains block the sunlight at the time of sunset.

Sun Pillars

Just before or after sunset, we notice a thick stream of sunlight emerging vertically from the Sun. This vertical column of light is referred to as sun pillar and is due to the presence of light-reflecting snowflakes or ice particles in the atmosphere.
Have you ever noticed the sky at the time of dawn? During this period, the Sun slowly illuminates the sky. As the Sun's rays start penetrating through the air, initially they tend to get blocked by objects like clouds, mountains, and even treetops.
Similarly, just before sunset, when the Sun starts fading from the sky, the rays tend to get obstructed by the aforementioned obstacles. This solar phenomenon in which sunlight is partially hindered, gives rise to what is known as crepuscular rays.

What are Crepuscular Rays?

This is an optimal effect in which the Sun is partially eclipsed by objects like the clouds, causing several beams of light to emerge from areas that are not covered by the cloud. This can either be a hole or a small space between clouds that allow sunlight to escape and fall on the ground.
We can view those beams of light streaming from the cloud due to the presence of haze, airborne dust, and water droplets in the atmosphere. These light-scattering particles floating in the atmosphere highlight the path of sunlight, which causes formation of beams in the sky.
Viewing crepuscular rays gives a feeling of the Sun's rays emerging from a single point. So after looking at this sunlight-shining-through-the-cloud phenomenon, you may wrongly think that the cloud is emitting the rays.
In general, it gives a perception that the rays are radiating (some may say diverging) from a single point. However, this is just an illusion, since the light rays are always parallel to each other.
However, it is not just the clouds that can create this visually beautiful effect. As aforementioned, when the Sun hides behind the mountains, you can see the crepuscular rays.
You can view this effect right in your house if you have tall ceilings and sufficient amount of haze particles. When sunlight enters indoors, you can notice beams of light emerging through the window.

When Do They Occur?

When going for a morning walk, just after sunrise, one can notice this optical effect when the sunlight begins to peak intermittently through the clouds and treetops. Also, when the Sun is closer to the horizon at the time of sunset, the Sun's rays look like they are dispersed in a fan-like shape.
Dawn and dusk is not the only time during which this solar phenomenon of crepuscular rays is observed. It can occur at any time during the day, particularly when the sky is cloudy.
Crepuscular rays are also sometimes referred to as God rays, as the radiating rays give a feeling of divine power just behind the cloud. Nevertheless it is a stunning display of light beams that appear to be emerging from a single point.

Anticrepuscular Rays

As the Sun starts setting in the horizon, we notice crepuscular rays radiating into the sky. Sometimes, these crepuscular rays are seen meeting at a singular point on the opposite side of the horizon.
These are known as anticrepuscular rays and are a spectacular sight to behold. However, these rays are not easily visible as they are much fainter than crepuscular rays. Also, to catch a glimpse of this phenomenon, right conditions need to exist. Too much dust particles in the atmosphere considerably reduces the chances of viewing anticrepuscular rays.
So the next time you see the Sun setting in the west and view the crepuscular rays, don't forget to view the east side of the horizon. I am sure you will see anticrepuscular ways converging on the opposite side.