Why is the sky blue?

Taken near the bottom during Summer hike from The Valley to Nevada Falls in Yosemite. 2012

Light from the Sun looks white, so why does the sky look blue? Light from our star, the Sun, is made of many different frequencies, or colors of light.  When light from the sun hits Earth’s atmosphere it scatters off of molecules in all directions.  This effect is known as Rayleigh Scattering.

Rayleigh Scattering is more effective at short wave lengths.  Blue has the shortest wavelength of visible light of all visible light, therefore, we see the sky as blue.

It just so happens that Earth’s atmosphere is made up to scatter the highest frequency of light that is visible to the human eye.  This is probably also an adaptation all our own.  If we had keener eyes, maybe we would be able to see a purple sky instead.  Next time we’ll talk about why sunsets are different colors.


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