Why The Sky Is Blue, According To Science

“That's a misconception, Lennie. The sky is everywhere, it begins at your feet.” -Jandy Nelson

There are all sorts of explanations that people give for why the sky is blue. Some say that it’s because of the fact that oxygen is a light blue gas. Others contend that the sky reflects the blue ocean, giving it a comparably blue color. Still others place the blame on sunlight itself, alleging that it’s naturally slightly blue in color. All of these science-y sounding explanations, compelling though they might be, are way off the mark. If they were correct, after all, you wouldn’t have reds during sunrise and sunset!

From very high altitudes in the pre-sunrise or post-sunset skies, a spectrum of colors can be seen, caused by the scattering of sunlight, multiple times, by the atmosphere. Public domain image.

 

Instead, it’s a combination of three factors that make the sky blue for us:

1. Sunlight is made of many different wavelengths of light.
2. The small atmospheric molecules scatter that light, but scatter short-wavelength light more efficiently.
3. And the human eye has three types of cone (and one type of rod) that allow our brains to interpret color.

Put them all together, and a blue sky is the net, inevitable result.

When the Sun is high overhead, the sky towards the zenith is a much darker blue, while the sky towards the horizon is a lighter, brighter cyan color. This is due to the larger amount of atmosphere, and the larger amount of scattered light, that is visible at low angles on the sky. Image credit: Karsten Kettermann / Pixabay.