The sky is blue during the day, although it can be extremely light blue in the morning, orange and red at sunset, and dark gray at night. Even the blue tone varies across the globe and is dependent not just on geography but also on height and climatic phenomena.
However, the topic of why the sky is blue remains unresolved. Especially when we consider that the sun, which supplies light to the globe, is a light yellow tint that blinds you if you gaze at it directly. But there is a simple scientific reason for all of this.
There are two things involved:
- Light waves
Let me explain.
Light waves and Their Relation to Color
As we stated in the introduction, the color of the sky will be determined by the color of the Sun. Light, like sound, is a kind of energy that is transmitted through waves. However, there is a significant difference: sound requires a material medium to be transferred, whether solid, liquid, or gaseous, and it never does so via a vacuum.
Light, on the other hand, is an electromagnetic wave that can pass through a transparent material such as air and water in a vacuum. In turn, sunlight is made up of a plethora of ripples of varying wavelengths.
The wavelength is defined as the distance between two consecutive peaks of the same wave. Our eyes, on the other hand, can see a limited spectrum of wavelengths that correspond to colors ranging from red at the longest wavelength to orange, yellow, green, and blue at the smallest wavelength.
To give you an idea, the color green has a wavelength of around 550nm. As a result, we will witness light waves moving through the air based on the color of the Sun’s inclination.
The Earth’s atmosphere is a gaseous mixture of molecules that contains 78 percent nitrogen, 21 percent oxygen, 1 percent argon and water vapor, and traces of other gases. There are also dust particles, ice crystals, and ash… Furthermore, the atmosphere is denser near the Earth’s surface, influencing the color of the sky.
Light travels in a straight line in a vacuum because there is nothing to disturb it. Instead, when light enters the atmosphere, it may collide with a grain of dust or a molecule, in which case one of two things can happen:
First. if the size of the dust grains and water droplets is significantly greater than the wavelength of visible light, they will act as mirrors, reflecting the incident light in different directions but not changing its color.
Second, when a light wave collides with a molecule that is smaller than the wavelength of visible light, the molecule can absorb the light and then radiate it in any other direction. This is referred to as dispersion. However, molecules scatter short-wavelength or blue-wavelength light considerably more efficiently than red long-wavelength light. Lord John Rayleigh, a scientist, studied this mechanism around 1870, which is why it is known as ‘Rayleigh scattering.’
Why The Blue Sky
We can conclude from the previous facts that the blue sky is caused by Rayleigh’s Scattering. As a result, when sunlight passes through the atmosphere to reach us, most of the long wavelengths of red, orange, and yellow light pass essentially unchanged.
However, many shorter wavelengths of light are dispersed by gaseous molecules in the air. As a result, if we gaze at any region of the sky, we will see some of that scattered light, which is blue, and therefore we will see the blue sky as well. The light that comes directly from the Sun, on the other hand, appears yellowish because it has lost some of its blue colors.
We already know why the sky is blue. However, when you look at the sky from a point closer to the horizon, it will look a little less blue. To get to us, the light from the sky has to go through, in this case, a lot of air. This causes it to be spread out again. Thus, the light that comes to us from the sky near the horizon will look less blue or white.
What makes the sky red at sunset?
Another thing to note is that as we get closer to the Sun’s horizon, it will take more and more of our atmosphere for light to get to us. This is because our atmosphere is very thin compared to the Earth’s radius. Color changes because light from short wavelengths (blue and green) is getting a lot spread out. Only light from red tones reaches us, so the color of the Sun changes.
The sky is blue at certain times of the day and reddish or orange at other times.