Why is the sky red in the summer evening? Why do people say it's Xia Hong?

Because of the refraction of the sun. Sunlight that does not shine at sunrise is red. When this red light shines on the clouds, it becomes red clouds. This is Xia Hong. Part of the sunlight penetrates the clouds, and the other part does not penetrate, but refracts back, so the clouds look red or other colors.

In the morning, the sun is in the east. If there is red light, it is mostly at the zenith or west. That is to say, there are low clouds at the zenith or west. The weather always changes from west to east, and this low cloud must be slowly approaching the local area, indicating that rainy days are coming;

On the contrary, the sun is in the west at night, and if there is red light, it is mostly in the zenith and east. Then, this low cloud will continue to move eastward, farther and farther away from the local area. If it rains, it won't rain locally, so it's sunny.

Extended data:

As the saying goes, it can't be burned early, but it will burn thousands of miles later. It means that if a flame cloud appears in the morning, the weather may get worse; It will appear at night and be fine the next day.

Flame clouds are red clouds that appear at sunrise or sunset. It belongs to low cloud and is one of the phenomena of atmospheric change. It often appears in summer, especially around sunset after a thunderstorm, in the west of the sky. The appearance of flaming clouds indicates that the period of warm weather, abundant rainfall and flourishing biological growth is coming.

References:

Baidu encyclopedia-huoshaoyun