Sun flail wind and moon flail rain explain how the weather will change.

The solar flail and the lunar flail are called the solar halo and the lunar halo respectively in meteorology.

A halo is a phenomenon of light formed when sunlight passes through ice crystals in clouds and is refracted, forming a ring around the sun or moon. What appears around the sun is called a corona, which is usually colorful, ranging from red, orange, yellow, green, blue, indigo, purple and other colors from the inside to the outside. Sometimes the color is not obvious. The large ring formed around the moon is called a halo, and is mostly white. The clouds that form the solar and lunar haloes are usually cirrostratus clouds. This kind of cloud is composed of countless small ice crystals. It is a high cloud with a wisp structure. The cloud height is about 6 kilometers or more.

The proverb "The sun flails the wind, the moon flails the rain" means that when the sun halo or moon halo appears in the sky, there will be wind and rain in the local area. It has been verified that its forecast accuracy is relatively high.