Why is the Sky BlueOctober 9, 2017
The sky has always intrigued and called humans to discover the unimaginable wonders lying within nature. But what truly provokes human desire and the thirst for knowledge is the fact that despite the millions of problems and challenges faced by humans in their everyday lives, some of which seem insurmountable; we can always look up to remind ourselves that the greatest things in life never change in the slightest even during the worst of circumstances. But the truth is that human greed has crossed all limits in the present times and it has successfully managed to change even the ever-constant sky by clouding its beauty with toxic pollutants and a host of other things. But for those of us still untouched and innocent about the number of ways the sky can be obscured by pollution, the endless beauty of the blue skies creates a million questions waiting to be answered. Of course, Science and Technology have fully uncovered the secret behind the skies appearing blue to human vision in the daylight. Below is a detailed explanation backed by genuine scientific facts about what humanity today knows to be the contributing factors to the
blue color of the sky:
The very simple explanation as to why human eyes see the sky as blue during daylight is because the molecules contained in air choose to scatter blue light from the light spectrum and this blue light is within the human line of sight. Although the sun gives out pure white light, in reality, it contains 7 colors, each possessing their own wavelengths. Since the human eye has three receptors that can view three colors namely, red, green, and blue; when we look up at the sky, our eyes see blue scattered by the molecules. Similarly, during sunset, the red wavelength comes into the visible spectrum which is why this time of day is perceived as Orange by human vision. The fact that we’re bestowed with the ability to view and enjoy beautiful colors helps us to fathom the infinite sky in a bright, captivating blue.
The fact that white light is actually 7 colors was established a long time ago by the prism experiment wherein a uniquely shaped crystal namely a prism was taken and the white light passed through it. Instead of coming out how it went in, the white light was forced to split into 7 different colors. This experiment proved the fact that light usually goes on its way in a straight line unless it is faced with something that forces it to split. Objects that force it to split include:
• Mirrors: They reflect light thus enabling us to see a reflection of ourselves.
• Prisms: They bend light and show us the split.
• Gaseous Molecules in the Atmosphere: These scatter one or more colors in white light thus helping us perceive the color of an object.
Sunset and Sunrise:
You may have noticed that the bright blue is omnipresent and that the sky changes color during weather changes and during different times of the day. Sunset and Sunrise are particularly significant. During these two occasions, the sun is located very close to Earth’s horizon. The pure white light from the sun needs to fight against the atmosphere to reach human vision during these times of the day. As such, the blue wavelengths are scattered and lost whereas the red colors successfully pass through and create a beautiful combination of reds and orange, and occasionally a green tinge. Thus, sunrise and sunset beckon people to visit such places that offer a clearer view of these striking phenomenon.
A little about the Atmosphere:
What molecules in the atmosphere expertly scatter light and give us the privilege of viewing the sky as blue during daytime? There are numerous gases in the Earth’s atmosphere along with other materials and moisture. Dust, Pollen, Oceanic Salt, and lately toxic pollutants have joined the otherwise pristine air that provides us refreshing Oxygen to breathe in. There is no specific composition to Atmosphere and various factors like location and weather play a role in determining how and when the blue skies are seen. But Nitrogen, Oxygen, Argon, and Water are the main elements that act as agents for scattering blue light across the skies.
The Sun Decides:
It all depends on how high the sun is and how farther away from the horizon it is. The higher the sun, the entire sky looks blue and in fact, the blue color looks brighter the more you look since there is more blue light. But when the Sun has dipped below the horizon, the light from the sun is slower in reaching the eyes. Airplanes that fly at great heights will show you how the blue light doesn’t reach fast but the reds are spread across the sky during mornings and in the evening.
Less Blue at the Horizon:
Observe The Horizon in The Picture
Imagine you’re out on a bright, sunny day and every time you look up you see a cloudless, bright, blue sky that makes you feel fresh and alive. Although the entire sky looks blue, if you would turn your attention to the horizon you will see the bright blue is much paler than overhead. This is because the light at the horizon had to fight through a lot of atmospheric molecules resulting in loss of the blue wavelength. The Blue was scattered and was re-scattered owing to the greater distance. As such, the horizon appears white while the rest of sky is blue as ever.
The scattering by air molecules is scientifically recognized as Rayleigh Scattering. According to the science, when specific particles with size less than one-tenth the wavelength of light are encountered by pure white light, Rayleigh Scattering occurs. The wavelength of light plays an important role in Rayleigh Scattering since lower wavelengths undergo most scattering. Oxygen and Nitrogen molecules present in the lower atmosphere are capable of scattering the lowest wavelengths of blue and violet. The Blue light exists in the wavelength of 450 NM which is the shortest in the light spectrum. Rayleigh Scattering, named after the physicist who discovered and proved this phenomenon gives us a clear, scientific view of the phenomenon.
The Sky is not actually Blue:
When humans view the sky above, it’s easy to conclude that the entire sky is blue. But this is not actually true. What we see as Blue in daylight is actually just the Earth’s atmosphere and is just a fraction of the Universe. When rockets, satellites, or astronauts leave this limited space, the blue sky no longer remains and instead becomes black. So, it’s safe to say that for us humans on Earth, the blue is actually an illusion, but no doubt a very beautiful illusion. Rayleigh Scattering occurs about 16 kilometers above where we stand and beyond that the blue color is no longer present.
What do Clouds do?
It is certain that Clouds obscure blue skies and play their part in scattering sunlight. Clouds, as we know are composed of water droplets which are larger than the wavelengths of light. So, Clouds scatter colors in a very different manner. Many factors determine to scattering of light by water droplets. Unlike the rest of the sky, Clouds appear white instead of any other color. Light scattered by Clouds are perceived by the human vision at all wavelengths since the difference between red and blue are insignificant. Blue Skies are a phenomenon unique to earth and other planets do not have this privilege.
All Objects get their Color in the same manner:
It’s not just the sky, but every single object on the Earth, whether Natural or Man-Made get their color according to the same principle. Let’s just say that’s how light works on the Earth or rather how human vision works. Sometimes some objects may appear to have a different color when viewed in a different light. For instance, red paint looks black under the influence of blue light. While humans enjoy this vibrant color play, it’s rather sad that other animals like Dogs see everything in Black and White.
What about the Ocean?
Yes, the azure blues of the Ocean also occur due to Rayleigh Scattering. However, only pure water appears blue. If impurities such as mud, algae, etc. contaminate water, it’s no longer blue. We know that clear blue waters are a rarity reserved for pristine untouched water bodies away from city pollution and contaminants. Although we were blessed with such beauty, we have successfully changed the color of the skies and of water bodies by letting our waste and toxins flow freely through them.
Now we know the simple yet very interesting phenomenon that gives the sky its blue color, let’s make a pledge to only live, love, and conserve this color play by playing our part in preventing environmental contamination that robs the infinite skies of its natural color. The same goes for the Ocean. As long as there are waste and pollutants being let into the water, the Ocean will not be able to reflect the blue. Happy skies and happy seas deserve to remain blue everywhere.