Ruth Netting

The light from the Sun looks white. But it is really made up of all the colors of the rainbow. All light travels in a straight line unless something gets in the way to: reflect it (like a mirror); bend it (like a prism); or scatter it (like molecules of the gases in the atmosphere).
Sunlight reaches Earth’s atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth’s atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.