Why is the Sky Blue?

Why is the sky blue?  That's a question that is often asked by kids and often answered incorrectly by parents and unfortunately teachers.  The common misconception is that the sky is blue because the oceans have a bluish tint to them.  Supposedly this bluish tint reflects blue light to the sky, causing it to appear blue.  This is, of course, completely incorrect.  The blue color of the sky has nothing to do with the color of water.  If it did, then the following should also be observed.

1.  The sky in Kansas or the middle of Asia should appear green or brown or whatever the common ground color is.  If the oceans cause the sky to appear blue but there is no water nearby, why would your sky appear blue?

2.  If the oceans are reflecting blue light upward, why are clouds white?  Shouldn't they also appear blue?

Somehow these questions are never brought up in the "why is the sky blue" discussion.

Tanvir Hasan.M [CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)]

So why is the sky blue?  The sky is blue due to the composition of our atmosphere.  The Sun emits all colors in the visible spectrum (think colors of the rainbow).  Red, yellow, orange, and green light all pass through the atmosphere unaffected.  Blue light however has a shorter wavelength and is scattered by particles in the atmosphere.  Blue photons (light particles) bounce around the atmosphere before they reach your eye on the ground.  Since they bounce around, everywhere you look you will see blue photons just reaching your eye.  Therefore the sky appears bluish.  The oceans play no role in this.

Now here's the tough question.  How do you explain this to a 5 year old?  My daughter has yet to ask me this question, but I'm preparing myself for the day she does.  How will I respond?  At this point I'm not exactly sure.  I suppose I'll start by saying the air around us causes the atmosphere to be blue, which is true, but provides no details.  If she's older and wants more details, then we can get into the details a bit more, but I'm guessing that a 5 year old will be satisfied with a simple, yet correct, response.

Here are a couple of other questions to ponder.  Why does the sky appear reddish at sunset and sunrise?  Why does the ocean/water appear bluish?  I'll address these in future posts.  

The moral of this story is to educate yourself before answering your kids.  If your kids ask you questions that you are not entirely sure of, don't make something up or go with what you think might be the answer.  Don't plant a misconception in their heads that may stick for 30, 40, or 50+ years.  Do the right thing and say "I don't know, but let's go look it up together".  Do this and you are an awesome parent.