The sky appears blue because of a phenomenon called Rayleigh scattering. When sunlight enters the Earth's atmosphere, it is made up of many different colors of light. Each color has a different wavelength, with blue light having a shorter wavelength compared to colors like red or yellow, which have longer wavelengths.

As sunlight passes through the atmosphere, it interacts with gases like nitrogen and oxygen. The shorter wavelengths of light (like blue) are scattered more widely in all directions by these molecules. This scattering process causes the blue light to spread throughout the sky, making it appear blue to our eyes.

The reason why we don’t see the other colors as much is because they are scattered less. Red, orange, yellow, and green light are scattered, but not to the same extent as blue light. While the scattered blue light is spread out in all directions, our eyes are particularly sensitive to it, so it dominates our perception of the sky.

Interestingly, during sunrise and sunset, the sky may appear more red or orange instead of blue. This happens because the sun is lower on the horizon, and its light must pass through a thicker portion of the atmosphere. This longer path causes the shorter wavelengths of blue and green to scatter out of our line of sight, leaving the longer wavelengths (like red and orange) to dominate.

The sky is blue because of the way sunlight interacts with Earth's atmosphere and how our eyes perceive the scattered light. The scattering of blue light is a fundamental part of the Earth's atmospheric dynamics.