Snow is one of the most celebrated natural substances in the world. At times, it symbolizes change and transformation, because it covers everything in pristine white, as though it were giving everything a fresh start, and a new beginning. On other occasions, it’s used to depict an array of human emotions in literature and poetry. Say the word ‘snow’ in your head and there’s a good chance that the first thing that comes to your mind will either be a picture of snow-capped mountains or a pleasant image of small, fluffy white particles falling from the sky in the winter.
The most immediately obvious thing about snow is its white color, but have you ever wondered why snow, which is nothing but a cluster of countless tiny ice crystals, is so flawlessly white? Shouldn’t it appear more like ice?
There are two elements that influence the color of snow: color theory and the refraction of light. Let’s quickly explain color theory first…
Everything that we see around us has a color as a result of its constituent particles; more specifically, it depends on the vibration frequencies of the atoms and molecules that make up the object. When a light ray of a given frequency falls on an object, its constituent particles absorb a certain amount of energy and emit this absorbed energy as heat. This essentially means that objects absorb different frequencies of light at different rates, which is what gives color to these objects.
An apple appears red because it absorbs the frequencies of every other color and reflects the red frequency; similarly, a piece of coal appears black because it absorbs all the frequencies of light without reflecting any.
So, what happens in the case of snow? Since it’s white, which frequency of light could it possibly reflect?
Refraction of light
Refraction refers to the change in the path of light upon entering a given medium. You see, light has a constant speed in air (300,000 km/s), but when it enters another medium, such as water, its speed slows down slightly, making its path bend. This is why a pencil kept in a glass of water appears to be bent from the point where it submerged.
Similarly, when light hits snow, it is refracted. Note that unlike water (which is transparent), ice is translucent, i.e. the light photons entering it don’t travel in a straight path due to interactions with the constituent particles of ice. This means that light exits from a point that is slightly off the straight line drawn from the point where it entered, giving ice a translucent appearance.
Snow is nothing but an array of these tiny ice crystals tightly packed together to acquire a random shape. It happens like this: when light enters through a layer of snow, it actually passes through a number of ice crystals, all of which alter the path of light to some degree, until the point where it comes out of the snow pile as a combination of different light frequencies, i.e. a combination of ever color of light… which happens to be white.
You surely must have performed the ‘splitting of white light’ experiment using a prism in your science class back in high school. An incident white light splits into its seven constituent colors through a phenomenon called the dispersion of light. Therefore, when the constituent particles recombine, as happens in the case of snow, what you see is a single beam of white light. This is why snow appears white, due to the combination of all frequencies of visible light emitted by countless ice crystals.
If not for this basic characteristic of ice crystals, the color of snow would have been anything but white. Think of how different-colored snow would have impacted so many things and ideas. Concepts of purity, innocence, winter, and getting a “fresh start” would certainly be different if snow around the world was green, orange, or bright pink!