Light travels in waves. These waves have different lengths and each length has a corresponding colour. For example, blue light waves are shorter than red light waves.
Key to understanding how ‘colour’ works, is the basic premise that light particles (known as photons) travel in a straight line. It only bends (refracts), bounces back (reflects) or scatters if it passes through or comes into contact with other particles. something
When the light rays from the sun enter the Earth’s atmosphere they bump into the gases and particles that make up our atmosphere. This collision scatters the light particles in every direction. As blue light waves are shorter and more easily derailed than longer light waves (such as red) they are the ones scattered most widely. This is why we see a blue sky most of the time.
Read full article originally published on NASA.