Why is the sky blue?


LAST UPDATED: May 31, 2020 by Ryan M

blue sky

This one is tough to explain in a few paragraphs, but here it goes.

To understand why the sky is blue, we first need to understand how sunlight interacts with the molecules in the atmosphere.

Sunlight appears white to the human eye, but it actually consists of many different colors. You can see these different colors of light in a rainbow or when light passes through a prism.

As the white light from the sun travels through the earth’s atmosphere, it collides with air molecules. The different colors, or wavelengths of light, are scattered by these collisions at differing amounts. This redirecting of incoming sunlight is called scattering.

The blue light (shorter wavelength) scatters more than any other color (longer wavelengths), so the blue is the most visible to the human eye.

This is a brief explanation of why the sky appears to be blue.

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  1. It takes millions of years for the light from some stars to reach us.
  2. Astronomers discovered a star made entirely of diamonds in 2004 and named it Lucy, a nod to The Beatles.
  3. Almost every star in the sky is bigger and brighter than our son.


1. Phyisics.org – Why is the sky blue?
2. SpacePlace.NASA.gov – Why is the sky blue? 


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