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The Big Blue

January 15, 2010

Rheanna Sand

Why is it that when you hold up a glass of water it appears colourless, but when you look out onto a beautiful Caribbean vista, the water dances in unbelievable shades of blue? Is there something special about the sea that gives the big blue its name?

There is nothing that makes the ocean more blue than drinking water. Its just that there is so much of it that we see its true colour.

So what is the source of that true blue? One idea is that the ocean reflects the blue of the sky. Another is that there are dissolved ions, like copper, that give the water a blue tinge.

The water, in fact, is not reflecting the sky. I bet if you shone a floodlight on a crystal blue lagoon at night, you would still see that aquamarine colour.

And yes, there are many dissolved ions and other particles that may absorb, reflect, and scatter light, but this just causes variation in colour from sea to sea. But this is not the source of the blue.

In its typical unique style, water gets its colour in a way that is unlike most other molecules.

Colour corresponds to the length of light waves. Molecules will tend to absorb some light waves and reflect others. The wavelengths that are not absorbed are the ones we see, and give a substance its colour. Usually light waves interact with the electrons of the atoms, and not the inner nucleus.

Water, however, gets its hue from the vibrations coming from the nucleus of the atoms. The excited vibrations absorb red waves and not blue ones. This is the only known molecule to get its colour in this way.

As if I needed another reason to revere this gorgeous view...

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