Ask Josh: Why Is Snow White?

Meteorologist Josh Fitzpatrick has the interesting answer.

Most folks know I'm a huge fan of snow!  From a young age I've been fascinated by it.  I can remember catching snowflakes on a black piece of paper and looking at them through a magnifying glass.  It was at that time I wanted to know why is snow white in the first place?  That's exactly what Jeremy Walters of Pikeville asked me in an recent e-mail.

Ok, so the color of snow is white, or is it?  This seemingly simple weather question actually has an in-depth answer.  Snow is a collection of ice crystals which are translucent and yet snow on the ground and in the air look white.  To complicate matters, snow can actually appear blue, green, black, gray and even red (and the ever-infamous yellow snow, but that's a different story).  The answer to the question 'Why Is Snow White?' involves the electromagnetic spectrum and the properties of snowflakes.

Why is snow white if water is clear? Most of us recognize that water, in pure form, is colorless. With impurities, such as in a muddy river, water takes on multiple other hues.

Even snow can take on other hues as well depending on certain conditions. For instance, the color of snow, when compacted, can take on a blue hue. This is common in the blue ice of glaciers.

Let's go back for a moment and discuss the properties of snow and ice. Snow is tiny ice crystals accumulated and stuck together. If you were to look at an ice crystal by itself, you would see that the ice crystal is also clear. But snow is different. When snow forms, hundreds of tiny ice crystals accumulate together to form the snowflakes we are familiar with.

Some people have even asked what the record for the largest snowflake. But this is hard to quantify considering snowflakes as we commonly call them are more of a bundle of individual snowflakes. A layer of snow on the ground is also mostly air space. Lots of air fills in the spaces between snowflakes.

The reason we see snow in the first place is due to light. As snow falls through the atmosphere and lands on the ground, light is reflected off the surface of the ice crystals. Since the snow has multiple facets, some of the light is scattered.

Visible light from the sun is made up of a series of wavelengths of light on the electromagnetic spectrum that our eyes interpret as different colors. When light hits an object, different wavelengths of light are absorbed and some are reflected back to our eyes. To complicate matters, light passing through ice will not continue through the ice crystal without first changing directions or reflecting off an interior angle within the ice crystal.

No one really ever sees one snowflake at a time. Most of the time, we see huge collections of millions of snowflakes on the ground. As light hits the snow on the ground, there are so many locations for light to be reflected, that no single wavelength of light gets absorbed or reflected with any consistency. Most all of the white light from the sun hitting the snow will reflect back and still be white light. Therefore, snow on the ground appears white.

One other important point to remember is that snow is indeed tiny ice crystals. Ice itself is not transparent like the glass in a window, but translucent. Light does not pass through ice easily. Instead, it bounces around back and forth within the ice crystals. As the light inside an ice crystal bounces around off the interior surfaces, some light is reflected and other light is absorbed. With the millions of ice crystals in a layer of snow, all this bouncing, reflecting, and absorbing leads to a neutral ground. That means there is no preference to one side of the visible spectrum (red) or the other side (violet) to be absorbed or reflected. The sum total of all that bouncing leads to white.

And you thought it was a simple answer :-) 

Keep those great questions coming and comment away!  Thanks for reading!

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