Why Is Snow White?

Snowy, misty mountains appear thickly blanketed in white

Manuel Sulzer / Getty Images

Why is snow white if water is clear? Most of us recognize that water, in pure form, is colorless. Impurities like mud in a river allow water to take on multiple other hues. 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. Still, snow most often appears white, and science tells us why.

Varied Colors of Snow

Blue and white are not the only colors of snow or ice. Algae can grow on snow, making it appear more red, orange, or green. Impurities in the snow will make it appear as a different color, like yellow or brown. Dirt and debris near a road can make snow appear gray or black.

Anatomy of a Snowflake

Understanding the physical properties of snow and ice helps us understand the color of snow. Snow is tiny ice crystals stuck together. If you were to look at a single ice crystal by itself, you would see that it is clear, but snow is different. When snow forms, hundreds of tiny ice crystals accumulate to form the snowflakes we are familiar with. Layers of snow on the ground are mostly air space, as lots of air fills in the pockets between fluffy snowflakes.

Properties of Light and Snow

Reflected light is why we see snow in the first place. Visible light from the sun is made up of a series of wavelengths of light that our eyes interpret as different shapes and colors. When light hits something, different wavelengths are absorbed or reflected back to our eyes. As snow falls through the atmosphere to lands on the ground, light reflects off the surface of the ice crystals, which have multiple facets or "faces." Some of the light that hits snow is scattered back out equally into all spectral colors, and since white light is made up of all colors in the visible spectrum, our eyes perceive white snowflakes.

No one sees one snowflake at a time. Usually, we see huge millions of snowflakes layering the ground. As light hits the snow on the ground, there are so many locations for light to be reflected that no single wavelength consistently gets absorbed or reflected. Therefore, most of the white light from the sun hitting the snow will reflect back as white light, so we perceive white snow on the ground, too.

Snow is tiny ice crystals, and ice is translucent, not transparent like a windowpane. Light cannot pass through ice easily, and changes directions or reflects off the angles of interior surfaces. Because light bounces back and forth within the crystal, some light is reflected and some is absorbed. The millions of ice crystals bouncing, reflecting, and absorbing light in a layer of snow leads to neutral ground. That means there is no preference for one side of the visible spectrum (red) or the other (violet) to be absorbed or reflected, and all that bouncing adds up to white.

The Color of Glaciers

Mountains of ice formed by accumulating and compacting snow, glaciers often look blue rather than white. While accumulated snow contains a lot of air separating the snowflakes, glaciers are different because glacial ice is not the same as snow. Snowflakes accumulate and get packed together to form a solid and mobile layer of ice. Much of the air is squeezed out of the ice layer.

Light bends as it enters deep layers of ice, causing more and more of the red end of the spectrum to be absorbed. As red wavelengths are absorbed, blue wavelengths become more available to reflect back to your eyes. Thus, the color of glacier ice will then appear blue.

Experiments, Projects, and Lessons

There is no shortage of awesome snow science projects and experiments available for educators and students. In addition, a wonderful lesson plan on the relationship between snow and light is found in the Physics Central library. With only minimal preparation, anyone can complete this experiment on snow. The experiment was modeled after one completed by Benjamin Franklin.