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Why Is The Sky Blue? Blue Sky Explained, According to Science

Wondering why is the sky blue? Well then, you are in luck! With this comprehensive guide, we will help you to understand more about the natural world around you.

This guide will help you understand Rayleigh’s scattering of light in the atmosphere and its effect on the sky’s color. 

You’ll also discover the sun’s actual color and how its position determines the sky’s color.

After reading this, you’ll be able to sound like the most intelligent person at any party. You’ll also learn more about one of physics’s most overly complicated topics.

White clouds against a blue sky

Why Is The Sky Blue?

The color of the sky, whether it is blue, red, or pink, is directly related to the wavelength of colors. 

Before you ask, “What is color?” Well, simply put, color is light and the eye’s perception of visible light.

All light is electromagnetic radiation, but our eyes can only see a small portion of the light spectrum, which falls within the range of 400 and 700 nanometers—going from violet to red (aka the rainbow).

The Visible Light Spectrum
Red~ 625 – 700 nm
Orange~ 590 – 625 nm
Yellow~ 565 – 590 nm
Green~ 520 – 565 nm
Blue~ 500 – 520 nm
Indigo~ 435 – 500 nm
Violet~ 380 – 435 nm

Well, violet light has the shortest wavelength, but as you can see in the table above, blue is also on that side of the spectrum with short wavelengths. 

So, what happens when sunlight enters the atmosphere? This light is scattered in different directions thanks to the gases and molecules in the air.

Blue light is scattered more than other colors because of that (for instance, red light passes through without being much scattered). Thus, the sky looks blue most of the time.

Even though indigo and violet lights have similar wavelengths, these shorter wavelengths aren’t detected by the human eye. 

As a result, blue is the only color visible to humans in the sky when the sun is shining high above. Still, if you look at the horizon, you might see very light blue or even white because light has been scattered even further.

The Rayleigh scattering and why the sky is blue
Why is the sky blue? The Rayleigh scattering is the answer!

How Does Light Scattering Work?

When it comes down to it, the blue sky you can see during the day results from the dispersion of light rays. 

The human eye detects distinctive colors through these wavelengths, with seven colors visible in a rainbow during or after a rainstorm if the sun is visible.

Rainbows only appear when there is moisture in the atmosphere, so they can emerge in foggy or rainy conditions. 

Because sunlight is slowed down by passing through the water droplets, light rays are broken up through refraction into the band of colors the eye perceives as a rainbow.

Rayleigh’s scattering, the answer to why is the sky blue, is a phenomenon first named by the English physicist Sir Lord Rayleigh in 1871. 

The color of the light visible in the sky depends on various factors because air molecules are proportionally much smaller than the wavelength type.

As said, the colors seen in the sky are part of the electromagnetic spectrum. They are constantly polarized electrically, meaning that the positive and negative charges are separated. This causes the wavelength particles to vibrate at a certain speed or frequency.

When the wavelength makes contact with the air molecules, it interacts with the electric field of the air. As a result, it causes air molecules to move at the same speed. This contact is why the sky is blue as it prompts the molecule to produce radiation, which we perceive to be a specific color like blue.

The sun’s position around the Earth changes by the minute; that’s why the wavelength that can travel to our atmosphere changes. Gradually it becomes shorter as noon approaches and more light scattering occurs, so only blue wavelengths are seen.

Light dispersion is something that many of us learned about through Sir Isaac Newton’s light prism experiment in a science lesson. Not only is this the answer as to why is the sky blue, but it also explains the reason why the sun appears to be white!

White light shining on a light prism and turning into the rainbow

To understand the nature of light better, Newton would make a hole in the window cover in his room on a sun-drenched day. Once all other light was eliminated in the room, only the ray of light from the hole would remain.

Newton would then place a triangular prism with a square base made from glass directly in front of the hole. He then observed that the light would be broken into a band of 7 colors.

As a celestial body, the sun emits light from hydrogen undergoing nuclear fusion. This is the process of atoms fusing together to form another element due to exposure to intense pressure and heat. As a result of the reaction, hydrogen forms, and vast amounts of light are produced as byproducts.

Therefore, the sun emits light that contains all colors in equal amounts, combining them to form white light.

It is during light phenomena only, like rainbows, sun dogs, haloes, and sun pillars that moisture in the air exposes the colors that make up the sun’s seemingly white color.

The reason why the sky is blue, which is light scattering, is also the reason why we see beautiful sunrises and sunsets.

The Sun’s Position

As the sky changes its position in relation to the Earth during the day, the type of visible wavelength also changes. The sun is furthest away during dawn and dusk.

When the sun sits the lowest in the sky, it is the farthest away from you as the Earth spins on its axis around the sun, causing the transitions from day to night and vice versa.

As blue light rays are too short, they can’t cover the distance, so only the longest wavelengths, red and orange, are visible at this point, making the sky red.

During the peak of sunlight’s presence in the day, noon, the sun is the closest to the Earth and to you. Thus the sun’s proximity causes the blue color of the sky to be more prominent and deeper.

However, the varying shades of blue of the sky are also the product of other wavelengths mixing with blue, such as green.

Red sunset
Reddish-orange sunset

Gasses and Elements

The gasses and elements present in the stratosphere and troposphere are also part of the reason why is the sky blue, as they affect light rays.

Interestingly, on planets with thick atmospheres like Venus, the light is a bright yellow due to sulphuric acid, carbon dioxide, and nitrogen.

You can find bizarrely colored skies on other planets and moons, such as the orange sky of Titan, one of Saturn’s many moons.

Likewise, Mars has a reddish-pink sky due to its atmosphere. In contrast, to these vivid hues, some celestial bodies like Mercury and the moon have a black sky.

This is due to the fact that these celestial bodies have a thin or non-existent atmosphere. Thus these planets and moons reveal the black hue of outer space (or the absence of color), along with all of the stars and other orbiting bodies that we can only see at night.

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