Why do sunsets look red?
During the evening, when the sun is near the horizon we may see a beautiful sunset. The reds and oranges of a sunset are caused by the filtering action of the sky.
Sunlight, as we know, is made of many colors. We can see the colors that make up sunlight when we look at a rainbow. As sunlight passes through the atmosphere, the different colors are scattered by the air.
During the day, when the sun is directly overhead, its rays do not have to travel through as much of the atmosphere to reach the earth. The sunlight is scattered in such a way that we see more of the blue rays. But at sunset, when the sun is low in the sky, the light rays must travel through much more of the earth’s atmosphere to reach the viewer.
As a result, the shorter blue rays are soon scattered out and we can see more of the longer orange and red rays of sunlight – and we have a reddish sunset. The red color of sunrise is caused the same way. – Dick Rogers