Why Is the Sky Blue?
The daytime sky is blue because of what happens to sunlight as it enters the Earth’s atmosphere. When the Sun is low near the horizon as it rises or sets, the wavelengths have farther to go in order to reach your eyes.
This causes the shorter wavelengths you see during the day to scatter even more, clearing the way for longer wavelengths to reach your eyes. Sunlight is a mixture of all the colors you see in a rainbow.
As sunlight streams down to Earth, the tiny particles of air, dust, and water in the atmosphere scatter the different colors. The blue light rays are scattered the most. They are reflected to our eyes, and the sky looks blue.
The sky has its blue color only within 100 miles (160 kilometers) of the Earth. Outer space is black because there is no atmosphere to scatter the sunlight.