Science Facts

Is The Sky Really Blue? – Blue Sky Scientific Explanation

Light is an electromagnetic spectrum. When sunlight enters the atmosphere, the light scatters by the atmosphere. The atmosphere is mainly air molecules and trillions of air molecules. Air molecules scatter blue color more than the red and green color. If there was no atmosphere and no particles to scatter the light, the sky looks black.

The sun seems white. So the blue color of the sky is an optical illusion. It is due to the preferential scattering of light by the air molecules. There is the least amount of scattering when the sun is overhead, and hence the sky appears white. 

Is the sky really blue?

The sky doesn’t have any actual color because Earth’s atmosphere is transparent to visible light. As far as wavelengths go, the sky is bluish violet or purple. Our brain and eyes can not process this color, and the energy of this color is low. So we can not see this color. Sky color depends on the atmosphere and the sunlight effect.

Our sky is just an atmospheric color. With the atmosphere, the sky looks black as like the moon sky. The sunlight position and atmospheric particles are responsible for the various kind of colors of the sky. That’s why you see a red sky at sunrise, sunset, and night. Actually, the sky is not blue scientifically.

Why is the sky blue?

The atmosphere makes the sky blue. The atmosphere contains 78 percent of nitrogen, 21 percent of oxygen, and the rest carbon dioxide. It also contains dust particles, sand particles, fog, water vapors, etc. Also, there are so many types of particles in the atmosphere.

Now, what do these particles do to make the sky blue? When the white light from the sun reaches the atmosphere, the different color wavelengths will strike on that particle. Then scatter away strike on that particle everywhere. The size of the particles in the atmosphere matches with the blue wavelength light, and then the blue color scatters away the most.

What color do you think scatters more? Blue is one of the colors of light that scatters the most! As the light moves into the air, the blue-color light bounces all over the place in the sky. Tyndall effect is due to the scattering of light. Colloids show the Tyndall effect but not solutions and suspensions.

Light is scattered by dust, but light can be scattered by other particles, such as air molecules and water droplets. If we consider light a wave, we can say that these particles reflect the light waves in different directions. It’s like the particles are scattering the light in random directions.

When the light hits the prism, it separates into many different colors, and we have a rainbow. So, the light is white when it moves in a straight line until it hits the prism. Then, it bends, and we can see colors. If we consider light as a particle of photons, we say they absorb the photons and re-emit them in different random directions. Do you know what the wavelength of visible light is? The correct answer is the range is 400 nanometers to 700.

White light from the sun is falling on larger particles such as dust particles. It has three primary colors, which are red, green, and blue. The dust particle scatters all the colors equally. So as you can see, red, green, and blue are scattering equally in all directions. Most sunlight goes straight through, and only a small percentage is scattering by the dust particles.

The air molecules (nitrogen, oxygen) are smaller than the wavelength of visible light. The air molecule scatters the different colors differently. The blue color is scattered more than the green color, spread more than the red color. Why because different colors have different wavelengths and shorter wavelengths are more scattered than larger wavelengths.

The blue color has the smallest wavelength. It collides with dust particles and molecules. So it scatters the most, and the red color has the largest wavelength. That’s why it scatters the least. In fact, the blue color scatters 10 times more than the red color. This is known as preferential scattering, and it happens in particles that are smaller than the wavelength of visible light, such as air molecules. So that’s why we see the sky appears blue.

Physics explanation for the blue sky: Prism can break up the light into different colors. In this case, the white light from the Sun comes through, and then it hits a certain piece of material. A prism has a characteristic that different wavelengths will go through the prism in slightly different directions, called the index of refraction. It means that it will split out the red light. It won’t bend it as much. That’s maybe at 700 nanometers wavelength. But the purple and blue light, around 400 nanometers in wavelength, will bend much more the entire solar spectrum, water acting as a prism to see a rainbow.

The Sun has to be going through a rain cloud. It has to be going through water droplets, and then you’ll see the beautiful rainbow spectrum. Blue light is higher in energy culture than ultraviolet rays. That means it’s lower in wavelength as a wavelength around 400 nanometers.

On the other hand, the red light is lower in energy closer to the infrared and has a wavelength of 700 nanometers. Our brains make sense of this wavelength by experiencing it. As a shorter wavelength, the blue light scatters or bounces more, and that’s why you see the blue sky.

When the wavelength of a particular wave is less, it scatters more. And when the wavelength of a specific wave is large, the scattering of that wave is less. It is the relation that Lord Rayleigh had found out. The mathematical relation stated that the intensity of scattering is inversely proportional to the fourth power of wavelength.

Or in other words, the intensity of scattering is directly proportional to one by lambda to the power four.

Formula: Intensity ∝1/λ^4; Here, lambda is the wavelength.


Read More:


Baird, J. C.; Wagner, M. “The moon illusion: I. How high is the sky?”. Journal of Experimental Psychology: General.
Tyndall, John. “On the Blue Colour of the Sky, the Polarization of Skylight, and on the Polarization of Light by Cloudy Matter Generally.”
Lord Rayleigh. “On the scattering of light by small particles.” Philosophical Magazine.
Watson, J. G. “Visibility: Science and Regulation.” J. Air & Waste Manage.
Gibbs, Philip. “Why is the sky Blue?”. Usenet Physics FAQ.

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