By Sarah Stone
When you look at pictures of individual snowflakes, the snowflakes are clear. So why is snow white and not clear?
First, it's important to understand what's going on when we see certain colours. Visible light from the Sun or other light source comes in a variety of wavelengths that human eyes interpret as colours. When light interacts with an object, the wavelengths that the object reflects or absorbs determines what colour our eyes perceive. When an object reflects all the wavelengths of light from the Sun that are in the visible spectrum, the object appears white. Something like a fire engine appears red because the paint reflects back certain wavelengths in the red area of the visible spectrum, while absorbing the rest.
This now brings us to water, snowflakes, and snow. Pure water is quite clear, meaning the wavelengths of light more or less pass right through it, rather than being reflected back to your eyeballs. Individual snowflakes are somewhat clear, but a large concentration of these ends up being white, meaning all the light is reflected back, rather than passing straight through. So what gives?
The key here is the way that light interacts with the mass of complex shaped snowflakes and air known as snow. Much like with water, light bends when it enters into a piece of ice, causing ice cubes or icicles to appear murky even when made from clean water. The tiny snowflakes, or ice crystals, that make up a snow bank all each bend light somewhat like an ice cube, though not quite as uniformly due to varied and complex shapes.
So when one of these tiny, beautiful ice crystal formations bend light, that light ultimately encounters another ice crystal in the clump of snowflakes where it is also bent, and then another and another. The process continues until the light reflects back out of the snow, rather than passing straight through it to the ground. Some wavelengths do become absorbed in the snow, more so when impurities like dirt are introduced, but with fresh snow, the majority of the light waves will ultimately be reflected, and thus the sunlight will appear white to you.
All that said, you may have noticed that snow can also look blue under the right circumstances. The white appearance happens when light reflects off ice crystals only a relatively small number of times, not penetrating very much into the snow. However, light that manages to penetrate deeper into snow tends to see the longer wavelengths, which exist on the red end of the colour spectrum, get absorbed a little bit, leaving the shorter wavelengths on the blue side of the spectrum to be reflected back at you.
So what allows the light to penetrate more deeply in certain snow? How compact it is. This simultaneously fuses more of the snowflakes into larger bundles of ice and gets rid of much of the tiny air pockets in the snow, resulting in white-ish blue looking snow/ice.
- Contrary to popular belief, if you were to view the Sun from space (and managed not to damage your eyes in the process), you'd see that the Sun looks white in the human visible spectrum, not yellow as it looks when looking at it from the surface of the Earth. You can learn more about this here.
- Polar bears appear mostly white for the same reason snow does. Their fur is not actually white, but made up of hollow, translucent tubes. The light hits the hair and gets scattered around in a similar fashion to snowflakes, eventually getting reflected back out with very little absorption, making them appear white. In fact, polar bear skin is actually quite black. It used to be thought that the combination of translucent tubes of hair and black skin helped keep polar bears warm, but this has since been proven to be incorrect, with the fur doing a pretty amazing job of reflecting all the light off. In fact, in a 1988 study performed at St. Lawrence University in New York, it was found that a one-fifth inch strand of polar bear hair only manages to conduct 1/1000th of a percent of ultraviolet light directed through the translucent hair tube. What actually keeps polar bears warm is a combination of a very thick layer of fat (as much as 4.5 inches thick in some cases) and their dense fur. Their fur and fat is so effective as an insulator that they can easily become overheated in open air, even at extreme negative temperatures. Their fat layer also allows them to swim around in frigid waters where their fur does nothing to protect them from the cold, which is also why mother polar bears tend to try to avoid taking their cubs for swims until they've built up a good layer of fat. (Incidentally, contrary to popular belief, there is no difference between fur and hair.)
- In order for a snowstorm to be officially considered a blizzard by the National Weather Service, visibility due to the snow (whether falling or blown around ground-snow) must be reduced to less than a quarter of a mile, the wind must be blowing at more than 35 miles per hour, and the storm must last three hours or more.
- Georgetown, Colorado currently holds the world record for the largest snowfall in one day. On December 4th, 1913, the city became buried in 5.25 feet of snow (about 1.6 metres).
- The famous Iditarod Dog Sled Race only allows Northern breeds, such as Siberian Huskies and Alaskan Malamutes, to participate, a rule that came about after a competitor entered the race with poodles who ultimately didn't handle the conditions very well. This rule protects dogs who were not bred to handle the extreme cold weather experienced during the race.
- The record for the longest amount of time it took a dog sled team to finish the Iditarod is currently 32.5 days. Winners usually complete the race in eight to ten days. The last dog sled team to finish the Iditarod is given the Red Lantern Award. The award originated with the 1953 Fur Rendezvous dogsled race held in Anchorage, Alaska, and it refers to the lantern that is traditionally lit at the beginning of the race and not extinguished until the last team has crossed the finish line.
Sarah Stone writes for the wildly popular interesting fact website TodayIFoundOut.com. To subscribe to Today I Found Out's "Daily Knowledge" newsletter, click here or like them on Facebook here. You can also check 'em out on YouTube here.