Re: Why is the sea blue?

> Why is the sea blue?

There are two reasons for the color of the sea; both of them contribute to the answer.

A. The sea reflects the sky.

You have probably noticed that the sea is not very blue-looking when the sky is overcast. Water reflects and scatters the light that strikes it; this is shown by the fact that you can see your reflection in puddles. When the sky is brilliant blue, the sea is also, because it reflects the blue of the sky. A good answer to why the sky is blue has already been posted at MADSci.

B. The sea refracts light just as the sky does.

Blue light is more easily bent, or refracted, than red light; thus, light refracted back from the surface of the sea appears blue. Furthermore, when you are underwater the water around you appears blue because more blue light is scattered back to your eye than red light. Here are some professional shots to show what I mean.

The scattering of light by the air, or by water, is called Rayleigh scattering.