Why Is The Sky Blue?
Have you ever wondered why the sky is blue? Why does it turn reddish at dawn? Today I will try to answer all these questions.
As you well know, on a sunny and clear day the color of the sky is usually blue. However, the colors that we can glimpse in the sky throughout the day are very varied. From a lighter blue to gray or orange. But why is the sky blue?
While the Sun is a blinding yellowish-white, at sunset it is common to see it red and not so bright, so the western sky also appears that color. Thus, depending on the color of the sun, the color of the sky will change. I will explain it to you next.
While the Sun is a blinding yellowish-white, at sunset it is common to see it red and not so bright, so the western sky also appears that color. Thus, depending on the color of the sun, the color of the sky will change. I will explain it to you next.
The Waves Of Light and The Color Of The Sky
As I said at the beginning, according to the color of the Sun, this will be the color of the sky. And it is that light is a form of energy that is transmitted by waves, like sound. But with an important difference: sound needs a material medium, be it solid, liquid or gaseous to be transmitted, but it never does so through a vacuum.
Light, on the other hand, is an electromagnetic wave that can travel in a vacuum or through transparent media, such as air and water. In turn, the sunlight is composed of a multitude of ripples of different wavelengths.
Wavelength is the distance between two successive peaks of the same wave. On the other hand, our eyes can see a certain range of wavelengths and correspond to colors that go from red in the longest wavelength, going through orange, yellow, green, and blue until reaching violet, that is, the shortest wavelength we can see.
To give you an idea, the color green corresponds to a wavelength of about five ten thousandths of a millimeter. As a consequence, depending on the color by the inclination of the Sun, this is how we will see the waves of light through the air.
Light, on the other hand, is an electromagnetic wave that can travel in a vacuum or through transparent media, such as air and water. In turn, the sunlight is composed of a multitude of ripples of different wavelengths.
Wavelength is the distance between two successive peaks of the same wave. On the other hand, our eyes can see a certain range of wavelengths and correspond to colors that go from red in the longest wavelength, going through orange, yellow, green, and blue until reaching violet, that is, the shortest wavelength we can see.
To give you an idea, the color green corresponds to a wavelength of about five ten thousandths of a millimeter. As a consequence, depending on the color by the inclination of the Sun, this is how we will see the waves of light through the air.
Earth's Atmosphere and Blue Sky
The Earth's atmosphere is a mixture of gaseous molecules that contains 78% nitrogen, 21% oxygen, and 1% argon and water vapor, as well as traces of other gases. There are also dust particles, ice crystals, ash in suspension ... In addition, the atmosphere is denser near the earth's surface, which also influences the color of the sky.
In a vacuum, light travels in a straight line because there is nothing to disturb it. Instead, when entering the atmosphere, light can meet a grain of dust or a molecule, in which case different things can happen:
In a vacuum, light travels in a straight line because there is nothing to disturb it. Instead, when entering the atmosphere, light can meet a grain of dust or a molecule, in which case different things can happen:
- If the dust grains and water droplets are much larger than the wavelength of visible light, they will act as mirrors that reflect the incident light in different directions, but without changing its color.
- In case the molecules are smaller than the wavelength of visible light when a light wave collides with a molecule, it can absorb the light and then emit it in any other direction. This phenomenon is known as scattering. However, molecules are much more efficient at scattering short wavelengths of blue light than long-wavelength red light. This process was studied by the physicist Lord John Rayleigh around 1870, which is why it is known as 'Rayleigh scattering.
The Blue Sky
Based on the above, we can affirm that the blue sky is due to Rayleigh's scattering. Thus, when sunlight passes through the atmosphere to reach us, most of the red, orange, and yellow light, which are the long wavelengths, pass through almost unaltered.
However, much of the shorter wavelength light is scattered by gaseous molecules in the air. In this way, if we look at any part of the sky we will be seeing some of that scattered light, which is blue, that is why we see the blue sky as well. On the other hand, the light that comes directly to us from the Sun looks yellowish because it lost part of its blue color.
So now, I have already answered the question of why the sky is blue. However, when looking closer to the horizon, the sky will appear a paler blue. This is because to reach us, the light from the sky must pass through, in this case, a greater amount of air, therefore it is dispersed again. Thus, the light that reaches us from the sky near the horizon will then have lost part of its blue color, looking paler or whitish.
On the other hand, in orbit outside the Earth's atmosphere, the Sun appears white and the color of the sky is black. This is so because since there are no molecules that scatter light, all wavelengths of sunlight reach us equally, that is why the Sun looks white. In this way, the sky looks black because there is nothing to scatter the light.
However, much of the shorter wavelength light is scattered by gaseous molecules in the air. In this way, if we look at any part of the sky we will be seeing some of that scattered light, which is blue, that is why we see the blue sky as well. On the other hand, the light that comes directly to us from the Sun looks yellowish because it lost part of its blue color.
So now, I have already answered the question of why the sky is blue. However, when looking closer to the horizon, the sky will appear a paler blue. This is because to reach us, the light from the sky must pass through, in this case, a greater amount of air, therefore it is dispersed again. Thus, the light that reaches us from the sky near the horizon will then have lost part of its blue color, looking paler or whitish.
On the other hand, in orbit outside the Earth's atmosphere, the Sun appears white and the color of the sky is black. This is so because since there are no molecules that scatter light, all wavelengths of sunlight reach us equally, that is why the Sun looks white. In this way, the sky looks black because there is nothing to scatter the light.
The Color Of The Sky At Sunset
Finally, as the Sun is closer to the horizon, the light must pass through an increasing portion of the atmosphere to reach us, since the atmosphere is very thin compared to the Earth's radius. The color of the Sun changes because the short wavelengths (blue and green) are increasingly scattered, and only the light of red tones reaches us.
And that is the reason why the sky is blue at certain times of the day and reddish or orange at others :)
And that is the reason why the sky is blue at certain times of the day and reddish or orange at others :)
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