How does sunlight create different colors?
Sunlight may look white, but it is actually composed of all the colors of the visible spectrum. Each color travels as a wave with a specific length. Red light has the longest wavelengths and travels in relatively straight paths, while blue and violet light have much shorter wavelengths. As this light enters the atmosphere, it encounters the gases and particles that make up the air.
The atmosphere is primarily composed of nitrogen and oxygen molecules. These tiny particles are the perfect size to interfere with the shorter wavelengths of light. When the sun's rays hit these molecules, the blue light is redirected or scattered. This process is known as Rayleigh scattering, and it is the primary reason the sky is filled with color during the day.
Why do we see blue instead of other colors?
While the longer red and yellow wavelengths pass through the atmosphere with very little interference, the blue light is bounced around repeatedly. This scattering effect causes the blue light to arrive at the eye from every part of the sky rather than from a single direct source. Because this light is coming from every direction overhead, the entire atmosphere appears to glow with a consistent blue hue.
Although violet light scatters even more than blue light, the human eye is more sensitive to blue. Additionally, the sun emits a higher concentration of blue light than violet light. These factors combine to ensure that the sky looks blue to a typical observer. When the sun is lower on the horizon, the light must travel through more of the atmosphere, which scatters away the blue and leaves only the longer red and orange wavelengths for us to see.