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Hey, Brain Stuff, Lauren Vogelbaum here.

Someone gazing out at the ocean from the coast of Maine might see deep navy to midnight blue water. Very different hues than someone

squinting at the bright turquoise sea from a sunny beach on a Greek island. So why is the ocean

blue? And why does it come in so many different shades? Before the article this episode is based on,

How StuffWork spoke with NASA oceanographer Gene Carl Feldman, who pointed out that, first of all, quote, the water of the ocean is not

blue, it's clear. The color of the ocean's surface, for the most part, is based on depth, what's in it,

and what's below it.

That's right. All water is clear by its nature. But here's why it looks different in a glass versus from a beach. A glass of water appears clear because light passes through it with

little to no obstruction. But if a body of water is deep enough that light isn't reflected off the bottom,

it appears blue. Basic physics explains why. Visible light is made up of a spectrum of different

wavelengths. The longer wavelengths appear to our eyes as shades of red and orange, while the shorter

ones appear as blues and violets. When light strikes the

ocean, it interacts with water molecules and can be either absorbed or scattered. If nothing is in the

water except water molecules, the longer red portions of the spectrum are absorbed by the water.

The shorter, zippier blue wavelengths are more likely to hit something,

including water, and scatter, meaning they make it back to our eyes, meaning the ocean appears blue.

Violet wavelengths are even shorter and zippier, but there are fewer of them in sunlight,

and our eyes perceive the blue ones better.

At long distances, like near the horizon, another factor that we've actually talked about in a different episode, comes into play. A mountains appear blue in the distance, no matter what

color they are up close, because the air itself is made up of molecules that scatter those zippy blue wavelengths of

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