The phenomenon that causes the color of the sky to appear blue is called Rayleigh scattering. When sunlight enters the Earth's atmosphere, it interacts with air molecules and small particles. Shorter wavelengths of light, such as blue, scatter more than longer wavelengths like red. Consequently, when we look up at the sky, we see this scattered blue light dominating our view. The intensity of the blue color can vary due to factors like air pollution or humidity, which can scatter light differently. This scattering effect is a key aspect of atmospheric optics.