What is it that causes the sky to appear blue?
We can learn more about sunlight and how it interacts with the gas molecules that make up our atmosphere by studying how it works. While sunlight appears white to the unaided eye, it is actually a rainbow of colors mingled together. The electrons and protons inside air molecules oscillate as the sun travels through the atmosphere. This can be put to many different uses. When this happens, oscillating charges generate electromagnetic radiation with the same frequency as the incoming sunlight, but it is spread in all directions. When air molecule molecules divert incoming sunlight, it is known as scattering.
Blue has shorter wavelengths and higher frequencies than red, making them complementary colors in the visible light spectrum. When charged particles are exposed to all colors of sunlight, they oscillate more rapidly. Blue, on the other hand, is the most potent color for inducing this. Because blue light oscillates at a greater frequency, it scatters more readily than red light. The difference can be significant when dealing with small particles such as air molecules. The acceleration of a particle is proportional to the square of its frequency, and the intensity of dispersed light is proportional to the square of scattered light intensity. As a result, the luminous intensity of scattering is inversely related to the focal length (f4). Blue light scatters ten times more effectively than red light because of this fact.
We only see the light that has been reflected into our direction by the atmosphere when looking at an unrelated location in outer space. The sky seems blue because blue light is more common than red light in the environment. In actuality, violet light disperses far further than blue light. More sunlight penetrates our atmosphere as blue light because our eyes are more sensitive to blue light in the sky than violet light it gets.
When the sun is setting, we see the opposite effect: a lowering of the horizon. A human's eyes can only see a portion of the light since it has been deflected. Red wavelengths of sunlight can be seen because they move through the atmosphere with little scattering, whereas blue wavelengths cannot be seen due to their high scattering rate. When the sun is low on the horizon, it travels further through the atmosphere, creating more opportunities for the blue light to be scattered. The sun is reddening as it sets to give the impression that it is. Many factors contribute to a polluted sky that increases the scattering of blue light, including aerosol sulfate particles, organic carbon, or mineral dust.
The water droplets in a cloud are hundreds of times larger than the wavelengths of visible light. The amount of light scattered depends on how the light is refracted, internally reflected by the clouds, and diffracted around the droplets. This particle's dispersion of blue and red light differs just a little from that of gas molecules. When clouds are set against a blue sky, they seem white instead of blue because of the scattered light our eyes receive.
Because of atmospheric scattering, a planet without a starry sky is impossible. Images of the moon taken by Apollo astronauts show them and the surface is bathed in sunlight, but the sky above them is pitch black due to the distance between them and the Sun.