Because the sky is blue?

When light passes through a prism, its spectrum is divided into seven monochromatic colors, as a rainbow of colors arises. The atmosphere plays the same role as the prism, acting where the sun's rays collide with air, water and dust molecules and are responsible for the dispersion of the blue wavelength of light.

When we perceive the color of an object, it is because it has diffusedly reflected or scattered the wavelength associated with light of a particular color. For example, a green leaf uses all colors in the spectrum to make photosynthesis except green, which is reflected.

Due to their small size and structure, the tiny molecules present in the atmosphere best diffuse waves with shorter wavelengths, such as blue and violet.

Throughout the day blue light (shorter wavelength) is scattered about ten times more than red light (longer wavelength).

Blue light has a frequency that is very close to the resonant frequency of atoms, unlike red light. Therefore, blue light moves electrons in the atomic layers of the molecule much more easily than red. This causes a slight delay in the blue light that is re-emitted in all directions.

When the sky is foggy, foggy or smoggy, there are oversized particles that disperse all wavelengths equally, so the sky tends to turn whiter due to the association of monochromatic colors.

In a vacuum that exists outside the vicinity of planet Earth, where there is no atmosphere, the sun's rays are not scattered, so they travel in a straight line from the sun to the viewer, so astronauts see the dark sky as if it were always night.

Why are sunset and dawn red?

When the sun is on the horizon, light takes a much larger path through the atmosphere to reach our eyes than when it is above our heads. The blue light on this path has been scattered almost entirely, the atmosphere acts as a filter, and very little blue light reaches our eyes, while the red light that is only transmitted reaches us more easily.

In addition, red and orange become much more vivid at dusk when there is dust or smoke in the air. This is because the dust particles are much larger than the others present in the atmosphere, causing scattering with light of close wavelengths, in this case red and orange.

Why are the clouds white?

In clouds there are droplets much larger than the wavelength of light, widespread scattering occurs throughout the visible spectrum and equal amounts of blue, green and red come together causing the white light to be scattered.