Why is the weather blue?

This is all caused by the atmosphere around the earth scattering sunlight. Because in the process of propagation, when light meets the interface of two homogeneous media, it will reflect and refract. So the color of the sky we see is actually the color of light scattering in the atmosphere.

Refraction refers to the phenomenon that when light is obliquely incident from one medium (such as water) into a second medium (such as air), part of the light deviates from the original path at the interface and forms an angle with the original path. Ptolemy, a Greek in the 2nd century A.D., was the first to study refraction quantitatively. He measured the correspondence between incident angle and refraction angle when light refracted from air into water. Although the experimental results are not accurate, he is the first person to study the law of refraction quantitatively through experiments. 162 1 year, the Dutch mathematician W. Snell accurately determined the law that the ratio of the cotangent of the incident angle and the refraction angle is constant through experiments, that is, csθI/csθt = constant.