The sky appears blue to the human eye because of a phenomenon called Rayleigh scattering. This occurs when sunlight is scattered by the molecules of the Earth’s atmosphere. The short-wavelength light, such as blue and violet light, is scattered more than the longer-wavelength light, such as red and orange light. As a result, more of the blue and violet light reaches our eyes, making the sky appear blue.
Rayleigh scattering is similar to the way a prism separates white light into its component colors, known as a rainbow. The difference is that instead of a prism, the atmosphere is scattering the sunlight. The blue color is caused by the shorter blue light waves being scattered more than the longer red light waves, this is why the sky appears blue.
It’s worth noting that the color of the sky can change depending on the time of day, weather conditions, and location. At sunset or sunrise, the sky can appear red, orange, or pink due to the longer-wavelength light being scattered less and reaching our eyes. Additionally, the sky can appear gray or white during overcast or hazy conditions, as the light is scattered by the clouds or pollution.