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One of the most unusual sights in the world is a glacier. Glaciers are found in mountain locations and in the coldest regions on earth. They are often a surprising and beautiful blue color. But snow is white, and water is colorless. So what causes glaciers appear to be blue? 

The answer has to do with the nature of light. Light was not well understood until the scientist Isaac Newton studied it in the 1660s. In experiments using prisms, he showed that white light is really made of seven colors, often represented by ROYGBIV, which stands for the first letter of each color in the rainbow (Red, Orange, Yellow, Green, Blue, Indigo,  and Violet). This discovery helped  explain why we see color in objects around us � and why we see rainbows in the sky! 

We see objects by reflected light. We see colored objects because they absorb and reflect different parts of light. When light hits an object, like a flower or a car, some of the colors are absorbed and others are reflected. The color that is reflected is the color we see, because our eyes have special cells that can tell one color from the other (unless you have are color vision deficiency � but that’s another story!).

When the light of all visible colors is absorbed by an object, the surface will appear black. When all visible colors are reflected off a surface, the surface will appear white. A blue object absorbs all colors of light except blue, which is reflected.

Snow is a collection of ice crystals mixed with gas bubbles of air trapped around them. When sunlight enters the top layer of snow, very little is absorbed. Because almost all the light is reflected, the snow looks white to our eyes. 

But as the light goes deeper into the ice, the red and yellow parts of the light are absorbed by the ice grains. The glacier reflects the blue light. The deeper the light travels into the ice, the bluer it appears.