ST. LOUIS – The sky is always changing colors—from a bright blue on a clear day, to red and orange sunrises or sunsets, or multiple colors of a rainbow—there’s a lot going on that we don’t always think about.
Why is the sky blue?
In short terms, it all has to do with light, air and our eyes. If you look at the sun through pictures—not through the naked eye—there is a glowing white light, which is made up of all colors of the rainbow. Maddie Earnest from the Saint Louis Science Center explained how it works.
“We shine light through (a prism), you could see that those colors that are made visible. All these different colors coming from the sun to the earth have to go through our atmosphere. As it goes through our atmosphere, it hits different gases and air,” she said.
All colors have a wavelength, so purple and blue scatter the sky. But wait—we don’t see purple in the sky? That’s where our eyes come in.
Our eyes have special cells called cones. They’re great for seeing blue, but not so good at seeing purple.
Sunrises and sunsets
The red and orange sunsets are created by a process called Rayleigh scattering, which is when the sun is low in the sky, close to the horizon. Colors are enhanced by air pollution, haze, particles, smoke, and dust in our atmosphere;.
As the sun goes down, it hits more layers, scattering those blue and violet rays everywhere. This leaves room for those other colors to have a longer wavelength that our allows our eyes to see.
Rainbows
The color of clouds involved several optical processes: Mie scattering, Rayleigh scattering, and refraction.
The sunlight is going through the water droplets that act like a prism, displaying a range of colors in the light.
Fun fact: Double rainbows are very rare, and the colors of the secondary rainbow are the reverse of the primary rainbow!
Color of clouds
Once again, it’s all about light.
Clouds are made of tiny droplets of ice. So when the light hits those, it scatters all over the place—and we see it as white, just like the white light. All the colors are being scattered in the same way.
More densely packed clouds start taking on more ice, leading to more liquid, and it actually starts to give the appearance of it being gray. Cumulonimbus, or thunderstorm, clouds can be up to 10-miles thick, so very little sunlight can actually go through. This leads to the sky becoming extremely dark.