Why is rosy clouds red?

I don't know if you have noticed carefully that colorful clouds often appear on the horizon around sunrise and sunset, and the sky is often red, which is commonly known as "flaming clouds" by the elderly. The glowing clouds are beautiful. Have you ever thought about its causes? Morning glow and sunset glow are caused by the scattering of light by air. When sunlight enters the atmosphere, it will scatter when it meets atmospheric molecules and particles suspended in the atmosphere. These atmospheric molecules and particles themselves do not emit light, but because they scatter sunlight, each atmospheric molecule forms a scattered light source. According to Rayleigh scattering law, light with shorter wavelength such as violet, blue and cyan in the solar spectrum is most easily scattered, while light with longer wavelength such as red, orange and yellow has stronger light transmission ability. So we see that the clear sky is always blue, and only red, orange and yellow light with longer wavelength are left on the horizon. After these rays are scattered by air molecules, water vapor and other impurities, the sky appears gorgeous colors.

The state of clouds and sky really implies a lot of weather information. There was no weather forecast in ancient times, and farmers' friends knew the weather by looking at the sky and the clouds.

Thin clouds in the sky are usually a symbol of good weather. Those low and thick clouds are often signs of rain and snow; The lightest and tallest clouds are called cirrus clouds. Cirrus clouds and cirrocumulus are very high, where there is little water, which generally does not bring rain and snow; There is also a kind of white clouds like cotton balls, called cumulus clouds. When the continuous rain and snow came, cirrus clouds gathered and a thin cloud gradually appeared in the sky. This cloud is called cirrostratus. Then, the clouds are getting lower and thicker. At this time, cirrostratus has changed its name and surname, so it's time to call it a high-level cloud. There are high clouds, and it often rains or snows within a few hours.

People can also infer the weather from the brightness of clouds. Around the sun and the moon, sometimes beautiful colored apertures appear, the inner layer is red and the outer layer is purple. This aperture is called halo. Solar and lunar halos often appear on the cirrostratus, and the high-rise clouds behind cirrostratus and nimbostratus are signs of heavy rain. Therefore, there is a saying that "the sun is dizzy in the middle of the night and the moon is dizzy at noon", which means that when cirrostratus appears with dizziness, the weather will get worse. There is also a colored halo smaller than the halo, called "Hua". The arrangement of colors is purple and red, just the opposite of halo. Rihua and Yuehua are mostly produced at the edge of cumulus clouds; From small to large in the middle, the weather tends to be fine; The central region of China is getting smaller from big to small, and the weather may turn rainy. In summer, after the rain clears, a colorful arc is often hung on the cloud curtain opposite the sun. This is a rainbow. People often say: "The east rainbow thunders and the west rainbow rains." If the rainbow is in the east, it will thunder and not rain; The rainbow is in the west and there will be heavy rain. There is also a cloud color, which often appears in the early morning or evening. The sun shone all over the sky and dyed the clouds red. This cloud is called Xia Xia. The morning glow is in the west, indicating that rainy weather is attacking us; The sunset glow in the east means that the weather has been fine in recent days. Therefore, there is a proverb "Don't go out at sunrise, but go to Wan Li Road at sunset".