Why are the Oceans Blue?

In my last post I discussed why the sky is blue.  It's a common question kids ask adults, and as a parent, you should have a simple, yet intelligent, response prepared.  If you don't have an answer, then do the responsible thing and look it up with your child.  If your child is asking why objects have a certain color, another common question is why are the oceans blue?  Is it because the sky is blue?  Does it have something to do with fish?  Is it caused by pollution?  Or is water just naturally blue in color?

The bluish Atlantic Ocean off the coast of Emerald Isle, North Carolina.

As with the blue color of the sky, this discussion begins with light.  Remember that although the Sun appears yellowish (Why?  Check in later for this discussion) it emits light of all colors on the rainbow.  Thus the surface of Earth receives red, orange, yellow, green, blue, indigo, and violet colored light.  Water is an excellent absorber of red, orange, yellow, and even green light.  Since the light is absorbed it doesn't reflect back to your eye.  Bluish light, however, is not absorbed very well by water so most of this light reflects back to your eye and the water appears blue to you.

The next time you are near water with your child, ask him/her why the water is blue?  Then, depending on their age, help them through the real reason.  At 5, my daughter is a bit young for this conversation on light, but it won't be long and she'll be able to grasp the physics behind it.

Here are a couple of sources, including one (the first) with a few ideas for exploration.

http://www.whyzz.com/why-is-the-ocean-blue
http://oceanservice.noaa.gov/facts/oceanblue.html