Ask My Sky Mom. Aviation wit and wisdom.

Hey Mom,

I have the same question that everyone asks sooner or later.  Why is the sky blue?  My mom never did come up with a very good answer.  Let’s see if you can!

Thanks,

Baby Blue

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Hey Baby,

Ya know, somehow that just doesn’t sound right.  Let’s try that again, shall we?

Hi Blue,

Well, the simple answer is that Rayleigh scattering is what causes us to perceive the sky as blue.  Rayleigh scattering refers to what happens when sunlight (which contains the full spectrum of colors, not just the blue we see) is filtered through and collides with the molecules (primarily nitrogen and oxygen) in our atmosphere.  The light is diffused and some of the shortest wavelengths, the blues, are scattered most efficiently due to this atmospheric makeup.

Interestingly, we can thank the same laws of physics for the colors of the sunset.  With the sun low on the horizon, we find ourselves viewing it through a much greater volume of air thus intensifying the degree to which shorter wavelengths are being scattered.  The longer wavelengths, the reds, will appear much stronger in comparison.  This is why the sun often looks so red as it dips down near the horizon.  As the sun sets, we’ll often see those vivid reds and oranges reflected off of the clouds.  In fact, this is also what causes the moon to look orange or red when that phenomenon occurs.

If you have the time and the patience and want to get further into the science of it, this is the long answer with the equations included.

Hope this helps, my friend.  Blue skies to you!

Mom

~ by myskymom on June 25, 2009.