Cold air forces molecules of water vapor into little liquid droplets which tend to condense onto any nearby particulate matter, such as pollen or dust. These tiny ice crystals are the baby versions of what soon become full-grown snowflakes. The crystals float through the sky and collide with molecules of water vapor. As vapor contacts the crystals, the water vapor skips straight from its state as a gas straight to a solid crystal, adding to the original nucleus of the snowflake. This process happens over and over again, building the snowflake from a nearly imperceptible crystal into a larger flake that, given the right conditions, falls to the ground and may cause you to utter a lot of swear words when you realize your gas-powered snowblower is broken.
Knowing all of this, it may still be difficult to believe that in a sky full of snowflakes no two are alike. On the next page you'll see how the flake-making process practically ensures that these little crystals are all unique, even when they fall by the billions.
As the very first ice crystals come together in a group of fledgling snowflakes, the new flakes often look strikingly similar. That's in large part due to the fact that ice crystals typically take a hexagonal six-sided lattice shape because of the way hydrogen atoms bond with oxygen to make water. Certain edges of the ice crystals are jagged.
These ragged, uneven areas attract more water molecules than the smoother and more uniform parts of the hexagon. Each little arm sprouts more of the same, growing into an intricate and uniform snowflake. If snowflake development stopped within the first few moments of birth, we'd wind up with a lot more flakes that look suspiciously alike. But snowflakes keep gathering more and more crystals, clustering together on top of one another in distinct patterns.
As those clusters of crystals continue their snowflake fiesta, other guests visit the flake-making party. They come in the form of environmental factors, notably humidity and temperature. Both play major roles in whether the snowflake gets bigger and bigger or fizzles out. You can imagine how critical temperature is to ice crystal formation and structure.
Between temperatures of 27 and 32 degrees Fahrenheit These are prototypical six-armed snowflakes that lack much visual interest. Drop the temperature a few degrees and you'll see needle-like structures. Hollow columns develop at even lower temperatures. And when it's crazy cold you'll see stars sprouting fern-like arms. Lower humidity tends to result in flatter flakes. Higher humidity means more crystal development in edges and on corners. Add some extra moisture at those really frigid temperatures and suddenly snowflakes may become mesmerizingly beautiful.
They contain a multitude of intersecting plates and needles and spaces, minute masterpieces falling from the heavens. A snowflake starts when a cold drop of water, less than 32 degrees, freezes onto a tiny piece of pollen or a dust particle in the sky.
This ice crystal then falls to the ground, and its shape changes and grows as it falls. It will twirl and swirl on its journey earthward, bumping into more water molecules that will freeze to it, creating an even larger ice crystal. The short answer is, yes, because each ice crystal has a unique path to the ground. They will float through different clouds of different temperatures and different levels of moisture, which means the ice crystal will grow in a unique way.
Temperature and humidity moisture in the air also impacts the shape of ice crystals. At 23 degrees, ice crystals look longer and more like needles or pillars. At 5 degrees, they are flatter, like plates. However, it is not likely every snowflake that has ever fallen has been different from each other. Snowflakes are hexagons, which means they have six sides or arms. Since snowflakes are made of water, their molecular structure is H2O two hydrogen and one oxygen atom. The water molecules look like Vs, and when they line up and freeze together, they will line up in a hexagon shape.
As more water molecules are added, they continue to add to the hexagon in an even way, so the hexagon doesn't change its basic shape, it just grows bigger. Snowflakes are amazing, and they also make for fun themed crafts and activities. Try out some of these! He tinkered with humidity and temperature settings to grow the two main crystal types and assembled his seminal catalog of possible shapes. In low humidity, stars form few branches and resemble hexagonal plates, but in high humidity, the stars grow more intricate, lacy designs.
Crystals grow into flat stars and plates rather than three-dimensional structures when the edges grow outward quickly while the faces grow upward slowly. Slender columns grow in a different way, with fast-growing faces and slower-growing edges. But the underlying atomic processes that dictate whether snow crystals will be shaped like stars or columns remained opaque. Libbrecht and the very small cadre of researchers who study this problem have been trying to come up with a snowflake recipe, as it were — a set of equations and parameters that can be fed into a supercomputer that would then spit out the splendid variety of snowflakes we actually see.
Libbrecht took up the pursuit two decades ago after learning of the exotic snowflake form called a capped column.
It looks like an empty spool, or two wheels and an axle. Soon, he was tinkering with snowflake-growing equipment in his lab.
His new model is the result of observations made over decades that he says recently began to gel. Imagine molecules of water arranged loosely, as water vapor just begins to freeze. If you were somehow viewing this from a tiny observatory, you would see the freezing water molecules begin to form a rigid lattice, with each oxygen atom surrounded by four hydrogen atoms.
These crystals grow by incorporating water molecules from the surrounding air into their pattern. They can grow in two main directions: up or out. The burgeoning crystal will spread outward. However, when its faces grow faster than its edges, the crystal grows taller, forming a needle, hollow column or rod.
Which of these processes wins as various surface effects and instabilities interact depends mostly on temperature. Pre-melting occurs differently on the faces and edges as a function of temperature, though the details of this are not completely understood. The instabilities and the interactions among countless molecules are too complicated to unravel entirely.
But he hopes his ideas will form the foundation of a comprehensive model of ice growth dynamics that can be fleshed out by more detailed measurements and experiments. Although ice is especially weird, similar questions arise in condensed matter physics more generally.
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