The sky appears blue to the human eye because of a phenomenon known as Rayleigh scattering. When sunlight reaches the Earth's atmosphere, it is made up of different colors of light, each with its own wavelength. Blue light has the shortest wavelength, while red light has the longest.
When the sunlight reaches the atmosphere, it encounters tiny particles, such as gases and dust, which are much smaller than the wavelength of light. These particles scatter the light in all directions, but they scatter the blue light more than the other colors because of its shorter wavelength. This causes the blue light to be dispersed in all directions, making the sky appear blue to us.
On the other hand, when the sun is closer to the horizon, its light has to travel through more of the Earth's atmosphere before it reaches us, and this causes the blue light to be scattered even more. This effect is called Tyndall scattering. This makes the sky appear more red, orange, and yellow during sunrise and sunset.
It's worth noting that the color of the sky can also change depending on the time of day, weather conditions, and pollution levels. For example, on a clear day, the sky appears a deeper shade of blue, whereas on a cloudy or hazy day, the sky may appear more white or gray.
In summary, the sky appears blue because of the scattering of sunlight by the Earth's atmosphere, particularly by the gases and dust particles, which is caused by the phenomenon of Rayleigh scattering.
