The Blue Sky: Why Isn't It Purple or Green?

Sunlight looks white, but it is actually a team of all the colors of the rainbow. As this light hits the Earth's atmosphere, it bumps into tiny gas molecules and bits of dust. Because blue light travels in shorter, choppier waves, it is much more likely to 'crash' into these molecules and scatter in every direction.

Because blue light is bouncing around everywhere like a pinball, when you look up, your eyes catch that scattered blue light coming from every part of the sky. This phenomenon is known as 'Rayleigh Scattering.' This explains why the sky isn't just blue around the sun, but appears blue from horizon to horizon.

If shorter waves scatter more, you might wonder why the sky isn't purple, since violet light has even shorter waves than blue. The answer lies in our eyes! Human eyes are much more sensitive to blue than violet, and the Sun naturally sends out more blue light than violet. Our brains essentially 'tune in' to the blue signal more strongly.