How the sky gets its color ?

In my previous post Blue Light, Phone and our Health I briefly explained the reasons why the sky above us is blue. it's due to the scattering of blue light which is light with low wavelengths and several other reasons. however, the post doesn't explain clearly how the process is. Moreover, as we know, the sky is not only blue but also reddish when the sun rises or sets. that's why I decided to write this post to find out in more detail how the sky gets its color!

image credit : Alvesgaspar own work, used under Creative Commons Attribution-Share Alike 3.0 Unported license
Usually, the term sky informally refers to a perspective from the Earth's surface; however, the meaning and usage can vary. An observer on the surface of the Earth can see a small part of the sky, which resembles a dome (sometimes called the sky bowl) appearing flattered during the day than at night. In some cases, such as in discussing the weather, the sky refers to only the lower, denser layers of the atmosphere. from Wikipedia

The sky basically is a term that refers to the s space above on this earth. although, there are many versions regarding how far the scope of the sky is. but what is clear, the sky is formless, it's just the space between objects in the universe and the limitation of human vision, so we only see what we can see.

As we all know, the sky looks like a dome or roof that protects us, sometimes blue, orange, yellow, or even green. so no wonder some people sometimes assume that the sky is a sturdy and perfect roof. however, the sky is just empty space. The sky that we often see has a variety of colors, and of course, we must be wondering what makes the color of the sky different.

Blue Sky

image credit : Gianni Crestani from Pixabay

The blue sky is a common color and we often see it in the sky. especially when the sun is bright in the morning and during the day where the blue color would be more clearly visible to our eyes.

There are at least 3 reasons why the sky has a blue color, the first reason is caused by sunlight. as we know that the sun emits light that carries various wavelengths, including x-rays, ultraviolet light, visible light, and radio waves. then, the earth's atmosphere blocks x-rays, ultraviolet rays, and radio waves, leaving only visible light to enter the earth.

Visible light is red, orange, yellow, green, blue, indigo, and purple. These seven visible lights are waves that aren't reflected back by the atmosphere.

However, even though they are not reflected back by the atmosphere, the seven visible lights will encounter various particles in the atmosphere such as oxygen, nitrogen, carbon dioxide, argon, ozone, and other gases. the meeting between visible light and these gas particles would result in light scattering. It's a process in which gas particles absorb the visible light of the sun and re-emitted in various directions.

In the light scattering process. blue, indigo, and purple are the three most scattered light by gas particles. this is because they are light with a short wavelength.

So that's why the blue, indigo and purple lights be the color of the sky. however, due to the greater quantity of blue light emitted by the sun compared to indigo and purple light. then the blue color in the sky becomes dominant. Moreover, the cone cells in the human eye that works to capturing color are more sensitive to blue than indigo or purple. so it's easier for us to see blue compared to indigo and purple in the sky.

Reddish orange

image credit : S. Hermann & F. Richter from Pixabay

I'm sure we are very familiar with the color of the sky as shown above. that's the color of the sky when the sun rises or sets

The reason what makes the sky to be reddish-orange is the position of the sun. it's close to the atmosphere. which means the sunlight that we see has made a long journey through the atmosphere. Because blue light is scattered more strongly by the atmosphere, it tends to scatter several times and be deflected away in other directions before it reaches us. This means that there is relatively more orange and red light left for us to see.

image made by me in Photoshop CS6

As an illustration. A person standing in position B is in the daytime where the sky is blue because there are lots of blue lights scattered in all directions. while in position A, it's the condition when the sun would rise. the person here / position B would see a reddish-orange sunrise because the blue light has mostly scattered away in the other direction, leaving red, yellow, and orange. the same process applies at sunset.

Purple/violet Sky

image credit : Deana Zelinová from Pixabay
purple sky is the color of the sky that we sometimes see. There are several factors that cause the sky to turn blue. The first is due to the optical illusion of a pink wavelength (reflective color) illuminating the base of the cloud (due to the low angle of the sun), and above the accumulating pink clouds is a dark blue sky. The combination of pink and dark blue could make the sky appear dark purple.

Another reason, there is an increase in the amount of particulate matter in the air due to the significant concentration of vapor from the storm, in contrast to the purple sky which is usually seen thin at dusk. purple skies caused by storm activity will produce skies that are completely purple. the events of the perfect purple sky had happened several times. for example, the purple sky that appeared before Hurricane Hagibis in Japan in 2019.

Green Sky

image credit : Free-Photos from Pixabay
The green sky color may not be familiar to many people but nevertheless, the green sky color really exists. one of the reasons why the sky looks green is because of the reflection of the green cloud color which is often associated with tornado signs as conveyed by Scott bachmeier from University of Wisconsin-Madison says that..

Green clouds only occur if the cloud is very deep, which generally only occurs in thunderstorm clouds. Those are the kind of storms that may produce hail and tornadoes.

Another factor that makes the sky green is the water droplets themselves. Water is great at reflecting blue light, but it could also reflect green light in the right conditions, such as when the sun shines down on them. The right thickness of the clouds, combined with the right diameter of the water droplets and the right timing could produce the perfect combination to turn the sky green.

So the green sky is not only a sign of a tornado coming. however, for those living in certain places, it's common that the green sky is a sign before the arrival of a tornado accompanied by hail.

Conclusion

The sky is one form of amazing beauty that exists in the universe. however, the sky is formless. the definition of sky only describes an empty space above us. which there are several versions regarding the extent to which the scope of the sky is. is it limited to the atmosphere or beyond? we don't need to argue about that.

The number of gases and particles present in the atmosphere layer, sunlight, the angle of the sun's rays, and many other variables make the sky have some different colors in certain conditions. the color of the sky not only gives a beautiful scenic effect to the human eye but sometimes it could be a sign for humans that danger will be coming....