If you were to travel 20 miles or so above the Earth's surface, the sky would appear black. What happens during light's journey to Earth that makes the sky take on a wonderful blue colour? "White" sunlight passes through our atmosphere, and molecules in the air, primarily nitrogen, are just the right size to scatter light from the blue end of the visible spectrum. The other colours travel to the ground with little interference. The blue light is scattered from molecule to molecule in the sky, until the light seems to be coming from every direction.