Why does the sky look blue?
The Sky is Blue
The sky appears to be blue because of the way the atmosphere interacts with the sun’s rays. White light, like that emitted by the sun, is composed of many different colors of light, each with its own corresponding wavelength.
On a sunny, clear day the sky is blue, although generally lighter blue near the horizon, while the Sun is a blinding yellowish white.
At sunset, the sun tends to be red and not so bright, and the westerly sky is also reddish. Here is a brief explanation.
Sunlight is composed of all the colors of the rainbow, so when we see a white light, we are actually seeing the light of all colors at the same time.
If the earth had no atmosphere, sunlight would reach our eyes directly from the solar disk and we would not receive diffused light.
The sky would appear as black as at night (astronauts can observe stars, the moon, and planets during the day because they are outside the atmosphere).
Why does the sky become multicolored at sunset?
At dusk, when the sun begins to set, its rays pass through a much greater distance into the atmosphere than when it shines directly at the zenith.
The larger particles suspended in the lower atmosphere disperse light so intensely that only the longer wavelengths, red and yellow, reach our eyes directly.
The Sun itself takes on the appearance of a scarlet sphere, and its rays, shining from a low angle, stain the bottom of the clouds with bright colors.
The color of a sunset (or sunrise) depends on the amount and size of particles in the air. For this reason, dust storms and volcanic ash eruptions often create magnificent twilights far away from where they occur.
What is Rayleigh scattering?
Light and the earth’s atmosphere, both of which are involved in the color of the sky. The atmosphere is mainly composed of gases, including oxygen (21%), carbon dioxide (0.03%) and nitrogen (78%).
But there are more suspended particles in the atmosphere, such as water, dust, ashes, pollen, etc.
The composition of the atmosphere may vary depending on location and weather conditions, but it is generally denser in the lower parts, i.e. near the Earth’s surface.
The sky is blue from the dispersion of Rayleigh
Light, on the other hand, is a type of energy that moves through waves. Light is a wave of vibrating electric and magnetic fields that are part of a wider range of vibrating electromagnetic fields, called the electromagnetic spectrum.
The secret of the sky being blue
The secret of the blue color of the sky is related to the composition of the sunlight -integrated by the different colors of the rainbow- and to the humidity of the atmosphere (the Sun is in charge of providing the air with its humidity).
With its heat, it causes some of the water on the earth’s surface to evaporate. In an invisible but incessant current, humidity is directed towards the sky from the oceans, seas, lakes, and rivers; from the soil, plants and the bodies of animals and man).
The great Newton
It was certainly during the 17th century that man discovered with astonishment the reason for the color of the sky. Until then, he had thought himself compact and unchanging.
Likewise, Newton’s color theory explains that white light is formed by the sum of all the colors of the rainbow.
when we see an object of one colour it reflects a certain wavelength and absorbs the rest. Reflects that color while absorbing the others.
At one end of the visible spectrum is red, which has the longest wavelength. That’s why its frequency is the lowest, that’s why we call the waves”infrared” with less frequency.
Also, at the other end, the violet wavelength is the shortest. Its frequency is the highest, which is why we call the waves with the highest frequency” ultraviolet”.
At night, the view of the sky is extremely dark, one might say black, and in the dark blue horizon. This is because there is almost no light, only the light reflected by the Moon.
The sky, in addition to the composition of light, owes its colour to another important factor: the atmosphere.
What makes the sky look blue?
Indeed, sunlight has to pass through the atmosphere to reach us. The tiny particles of dust and water in suspension.
In the air, they are smaller than the wavelengths of visible light, which are not large enough to repel the wave, but they do have the size to slightly deflect it from its original path.
This is known as scattering and the wavelengths of the blue end of the spectrum are shorter.
They are dispersed to a greater extent than those of the rest of the colors, and this gives the blue color to our sky.
To be exact, a third factor must be added to determine why we see the blue sky. This is our own physiology.
The sky should be violet, as the wavelengths of this color are even shorter than those of blue.
The sky blue in sight
If we don’t see it purple it’s because our eyes catch the color in their own way. They only have cells sensitive to three colors: red, green and blue, and the rest of the colors are perceived by combination.
That is because they excite several of these three types of cells at the same time.
Therefore, since our eyesight is more sensitive to blue than violet, it is the color we observe when we look at the sky.
Curiosities about the color of the sky
Why is the sky bluer today than it was yesterday? This is due to the variation in the proportion of suspended particles in the atmosphere.
Why is the sky bluer at the zenith (above us) than on the horizon? The sky on the horizon is whitisher because there is a greater diffusion of the longer wavelengths due to the greater thickness of the atmosphere in the horizontal direction.
In the direction of the zenith the thickness of the atmosphere is lower, and therefore the shorter wavelengths are more dispersed.
Why do you see the sky at the blueest zenith from a mountain? As we gain height, the white light scattering elements disappear, and so above us, the sky will be a more intense blue color if we see it from a mountain.
Why is the sky less blue the closer it is to the Sun? As the rest of the colors barely disperse in the atmosphere, we only receive them directly from the Sun. Thus, as we approach the position of the Sun we receive more of the rest of the colors.
Why is the sky reddish at sunset or sunrise? In the first and last hours of the day the Sun is very close to the horizon, so the sunlight will have to cross a greater distance to reach our eyes.
As a result, there will be more diffusion, but as the red colors (because they have a longer wavelength) hardly experience diffusion, we will see the sky of this color.
A great book I recommend is this.
- Tristan Gooley
- Edición Kindle
- Edition no. 0 (05/08/2014)
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