White light is made up of all seven colors found in the rainbow. When pure sunlight shines through the weather zone, water droplets and other moisture refract, or bend, the light. The refraction of pure sunlight causes the sky to appear blue.

Scientists call this “weather zone” the troposphere. This important part of the atmosphere is made of mostly nitrogen and oxygen. About three-fourths of the troposphere is nitrogen. Less than one-fourth is oxygen, or just about 21 percent. The remaining 1 percent is made of a gas called argon, and tiny traces of other gases.

When pure sunlight shines through these gases, blue light is scattered in all directions, and some bounces toward your eyes. A deep blue sky means that there is very little moisture in the troposphere.

A pale blue sky, or a gray sky, means there is lots of moisture in the weather zone. That is why gray skies are usually rainy skies.